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When it was required to use this instrument the vessel was stopped and the microphone lowered overboard to a depth of about 20 feet. This was the distance down from the surface at which submarine noises could be heard most distinctly. The operator on deck or in the cabin then adjusted the ear-pieces and sat listening for any noises coming through the water. Although the sea is a far better conductor than air, the range at which sounds could be heard varied considerably. On a calm day or night the noise of a ship's propellers could frequently be distinguished at from five to seven miles; whereas on a rough day, with the sea splashing and the wind roaring, it was often difficult to hear anything beyond half-a-mile.
[Illustration: FIG. 6.—Diagram showing essential parts of a portable hydrophone. A. Head and ear pieces, by means of which a trained listener hears submarine sounds. B. Flexible leads to enable an officer to verify reports from listener. C. Battery box, containing spare set of cells. D. Terminals. E. Terminals of spare cells. F. Flexible armoured electric cable which is lowered over side of ship. G. Metal case protecting the microphone H. H. Microphone or delicate receiver of submarine sounds, which is submerged (when required, but not when ship is moving) to a depth of about 18 feet, as in small diagram. The sound is detected by the microphone and transmitted up the cable F and wires B to the ear-pieces A.]
In fine weather a submarine could usually be heard at a distance of about two or three miles. There were, however, many microscopic noises of the under-seas which were picked up and magnified by this type of hydrophone. They were called "water noises," and often made it extremely difficult to differentiate between them and the sound of a moving submarine at a great distance. Later types were not so prone to these disturbing influences.
To describe here the different natural and artificial noises heard on a portable hydrophone is extremely difficult. One general statement can, however, be made. It is the noise caused by the rapidly revolving propellers of both surface ships and submarines that is the guiding factor in the work of detection by submarine sound. A destroyer travelling at full speed on a calm sea, when heard on a hydrophone resembles the roar of a gigantic dynamo. The sound does not alter as the distance between the stationary listening ship and the fast-moving warship increases or decreases; it continues to be a roar or low hum, according to distance, until it fades out of hearing altogether. The same statement applies also to a slow-moving cargo steamer, only in this case the single propeller is revolving very much slower, and, when listening on a hydrophone about two or three miles distant, each successive beat of the engines can be distinctly heard.
The simple movement of a vessel's hull through the water cannot be heard on a hydrophone. Therefore for detecting the presence in the vicinity of a sailing ship at night or in a thick fog this instrument is quite useless. The same drawback applies also to the location of a floating derelict or iceberg, and restricts the use of the hydrophone to faithfully reporting the presence of power-driven ships or special sound signals at a range of a few miles.
A German submarine heard at a range of about a mile on a calm night presents a curious sound which almost defies description. Its principal constituent consists of a "clankety clank! clankety clank!" at first barely distinguishable from the low swish of the water past the face of the submerged microphone, then louder when the sound has been distinguished and the human ear is on the alert. But when this sound was heard in war there was little time for analysing or noting. It was the call to action. The microphone was hauled to the surface and the chase began, a halt being made every half-mile or so for a further period of listening on the hydrophone. If the sound was louder the commander of the pursuing vessel knew that he was on the right track, and if the sound came up from the sea more indistinct the course was changed and a run of a mile made in the opposite direction, when the vessel was again stopped and the instrument dropped overboard.
Should this manoeuvre have placed the surface ship in close proximity to the submarine, one or more depth charges were released, and if the explosion of these damaged the comparatively delicate hull or machinery of the under-water craft, she had either to rise to the surface and fight for her life with her two powerful deck guns, or, if badly damaged, sink helplessly to the bottom, emitting oil in large quantities from her crushed tanks.
Before entering upon a description of the depth charge, however, there is more to say of the hydrophone, which has played such an important part in the defeat of the U-boats.
When the advantages of this instrument had been fully demonstrated in the stern trial of war, successful efforts were made to improve upon the original crude appliances. The "water noises" were reduced and, greatest improvement of all, the hydrophone was made "directional." By this is meant that when a sound was heard its approximate direction north, south, east or west of the listening ship could be more or less accurately determined. What this improvement meant to a vessel hunting a submarine in a vast stretch of sea will be easily realised. When the sound came up the wires from the submerged microphone the operator had simply to turn a small handle in order to determine from which direction the noise was coming.
If, for example, the sound was first heard away to the east, the instrument was turned to another quarter of the compass. Then, if the noise was plainer, the instrument was turned again until the sound decreased in intensity. In this way the line of maximum sound was obtained, and this showed the direction from the listening ship in which the U-boat was operating.
With the perfection of this invention the hydrophone section of the naval service came into being. Special courses in the detection of submarine sounds were instituted for officers and also for seamen listeners. The actual movements of a submarine under water at varying distances from a hydrophone were recorded by a phonograph, and records made so that the sounds might be reproduced at will for the education of the ear. Surgeons with aural experience estimated the physical efficiency in this respect of would-be volunteers for the hydrophone-listening service, and vessels were formed into special hydrophone flotillas, whose duties consisted of listening in long lines for submarines and when a discovery was made attacking them in the most approved tactical formation, with the aid of depth charges and guns.
A considerable measure of success attended these arrangements, and the author spent many cold hours listening at night for the sound of the wily submarine. On more than one occasion an exciting chase resulted.
It must, however, be pointed out that there is one great drawback to the successful use of the hydrophone. It exists in the necessity for the listening ship to stop before the hydrophone is hoisted outboard, it being quite impossible to hear anything beyond the roar of the engines of the carrying ship so long as they are in motion. Furthermore, all progress through the water must have ceased and the listening ship have become stationary before artificial sounds, such as the propellers of a submarine, can be distinguished from the natural noises of the sea water.
Now it will at once be apparent that not only does a stationary ship offer a splendid target for under-water attack, but also it allows a somewhat humorous game of hide-and-seek to be played between a hunting vessel and a hunted submarine.
Nearly all U-boats were fitted with a number of hydrophones and therefore were as well able to receive timely warning of an approaching surface ship as the surface ship was of the presence of the submarine. But the surface ship had the advantage of speed.
The result of all this was that when a German submarine heard a surface vessel approaching she dived to the bottom, if the water was not too deep or the sea-bed too rocky. Then shutting off her engines she listened. The surface ship, mystified by the sudden cessation of the noise she had been pursuing, also waited, and this stagnation sometimes lasted for hours. Then if the surface ship moved, as she was often compelled to do in order to avoid drifting with the tide away from the locality, the submarine moved also, and the one that stopped her engines first detected the other, but could not catch up to her again without deafening her own listening appliance. In which case the next move would probably be in favour of her opponent.
All of this is, perhaps, a little complicated, but a moment's pause for reflection will make this curious situation clear to the reader. And so the game went on, with decisive advantage to neither the surface ship nor the submarine. Darkness usually intervened and put an end to further manoeuvring, frequently allowing the submarine to escape.
A case of this kind occurred to a vessel, of a certain hydrophone flotilla, commanded by the author. For over four hours the U-boat eluded the pursuing surface ships by moving only when they moved and stopping when they too had stopped, darkness and a rising sea eventually favouring the escape of the submarine, which, a few hours later, was able to attack (unsuccessfully) a big surface ship less than thirty miles distant from the scene.
Nevertheless the hydrophone is a submarine instrument with a brilliant future. It has already been improved out of all resemblance to its original self, and more will undoubtedly follow. It is, however, purely an appliance for the detection of submarines when cruising beneath the surface, and not a weapon for their destruction. It should also be remembered that any improvement made in the efficiency of the hydrophone will benefit not only the surface ship, but also the submarine, for it cannot be supposed that under-water craft will be left without these wonderful submarine ears when their surface destroyers are equipped with them.
The alliance between the hydrophone and the depth charge is a natural one. The former instrument enables the surface ship to discover, first, the presence of a submarine in the vicinity, and, secondly, its approximate position. At this point its utility temporarily ceases and that of the depth charge begins. When a surface ship is hot on the track of a moving submarine she endeavours to attain a position directly over the top of her quarry, or even a little ahead, and then releases one or more depth charges according to whether the chance of a hit is good or only poor.
From this it will be apparent that whereas the hydrophone is the instrument used for the initial detection of the submarine, and afterwards for enabling the surface ship to get to close quarters with her submerged adversary, it is the depth charge with which the attack is actually made.
This weapon is really a powerful submarine bomb. It consists of several hundred pounds of very high explosive encased in a steel shell, with a special firing device which can quickly be set so that the charge explodes at almost any depth below the surface after being released from the above-water vessel.
The methods in use during the war for its release from the decks of surface ships were very diverse, the most usual being for a number of these weapons to be fitted on slides and held in place by wire slings which could be released by simply pulling out a greased pin or bolt.
When the depth charge rolled off the stern of the surface ship it sank to the "set depth" and then exploded like a submarine mine. The result was a shattering effect exerted through the water for several hundred feet around. If the submarine was close to the explosion her comparatively thin plates were nearly always stove-in. When she was over a hundred feet away, however, the rivets holding her plates together were often loosened, and the resulting leak frequently compelled her to come to the surface, where she could be destroyed by gun-fire.
It often happened, however, that neither one nor the other of these things occurred, but that the submarine's delicate electrical machinery was thrown out of order by the violence of a depth-charge explosion, even when a considerable distance away. With the electric engines used for submerged propulsion no longer available, and possibly the interior of the vessel in darkness, there were only two courses open. She could either rise to the surface and endeavour to fight it out with the aid of her powerful deck guns, or else sink to the bottom and trust to luck that other depth charges would not be dropped close enough to seriously damage her hull. In the open sea, however, the latter chance was denied because of the depth of water. Three hundred feet may be taken as the greatest depth to which an ordinarily constructed fighting submarine can safely descend without running a grave risk of having her plates crushed in by the great water pressure. Even at this depth the weight on every square foot of hull surface exceeds 8 3/4 tons.
If the damaged submarine rose to the surface the guns of her pursuers were ready and could generally be relied upon to place her at least hors de combat before the hatches of the under-water vessel could be opened and her own guns brought into action.
In shallow water where there was a fairly smooth bottom it generally happened that a submarine damaged by depth charges elected to sink to the sea-bed and trust to luck. This was also frequently resorted to as a means of eluding pursuit even when the U-boat was not damaged by the first few charges dropped. It was then that the hydrophones carried by the surface ships were again brought into use to ascertain if the submarine was still under way. When no sound was heard those on the surface knew that "Fritz" was lying doggo, or else that he had escaped. If a number of ships were available a few waited over the spot where it was considered the U-boat was lying, while the others scoured the surrounding seas in circles trying to pick up the sound of the runaway's engines if she had escaped in the melee. When nothing further was heard they returned to the scene and set about the work of systematically bombing the surrounding sea-bed.
As many as one hundred depth charges were dropped in quite a small area of sea and yet a submarine known to have been lying "doggo" in the locality was not damaged. In cases such as this other means, which will be described in a succeeding chapter, were then resorted to.
All the foregoing sounds very thorough and hopeful, but in fairness it must be said that submarine hunting is a heart-breaking task. The reader may have noticed that the method of depth-charge attack presupposes the surface vessel to have attained a position almost directly over the top of her enemy, a manoeuvre extremely difficult of achievement even with the most efficient hydrophone. Heavy seas, snow and fog have also to be taken into consideration, to say nothing of darkness, the presence of a second submarine, a surf-beaten rock or sandbank and the confusing sounds of passing merchant ships, making a difficult task more difficult, as will be seen when we come to the actual fighting.
CHAPTER VI
SOME CURIOUS WEAPONS OF ANTI-SUBMARINE WARFARE
ALTHOUGH modern war has shown that there exists no certain antidote for the submarine, it nevertheless brought into being many curious weapons of attack and defence. It is the purpose of this chapter to describe some of the anti-submarine devices used with more or less successful results during the protracted naval operations against the Central Powers.
INDICATOR NETS
Among the most important of these were the immense meshes of wire known as "indicator nets," which were used to entangle a submarine and then to proclaim her movements to surface ships waiting to attack with guns and depth charges.
[Illustration: FIG. 11.—Diagram showing principal features of a line of submerged indicator nets. AA. Two sections (100 feet in breadth) of thin wire-netting with a very wide mesh. B. Framework of wire rope holding each section of net in place by means of metal clips C. C. Metal clips which expand and release netting from rope frame when a pull of more than 100 lb. is exerted upon them. D. Line of invisible glass balls, or hollow floats, attached to a surface wire E, supporting by wires F, the nets which hang down from the surface vertically in long lines (1/2 to 1 mile in length and 50 feet deep). G. Heavy iron weights or sinkers holding down the nets by their weight when hanging in water. H. Wooden floats, attached to each section of net by wires I. J. Canisters of chemical which give off flame and smoke when exposed to sea-water. K. Lanyard attached to surface wire E. When a section of net is pulled out of its wire frame by a submarine passing through the line the float is dragged along the surface by the wire I. The lanyard is held back by being attached to surface wire E, and pulls a plug out of the canister J, exposing the chemical inside to the sea-water (see Fig. 12).]
These nets were made of specially light but strong wire, with a mesh of several feet. They were joined together in lengths of 100 feet by metal clips which opened when a certain strain was exerted on any particular section. Their depth was usually about 50 feet, and they were laid in lengths varying from a few hundred yards to two miles. Weights at the lower end and invisible glass floats along the top held them suspended vertically from the surface. The floats were kept in place by a wire hawser running along the top of the nets, and to this were attached, at intervals, wooden buoys containing tin cases filled with a chemical compound which, when brought into contact with sea-water, emitted dense smoke by day and flame by night.
The 100-feet sections were linked together, and to the top and bottom ropes, by the metal clips. These clips opened when a submarine headed into that part of the line. The result was that a section of net enveloped the bow of the under-water craft, was detached from the line and carried along, dragging its indicator float on the surface behind.
The indicator float, containing the chemical, was attached (1) to the section of net by a short wire and (2) to the top rope of the whole line by a lanyard, which, when pulled free, exposed the chemical contents of the canisters in the float to the sea-water. The float was then dragged along the surface burning furiously.
As there was nothing to materially impede her progress, a submarine would consequently be unaware that she had passed through a line of nets and was actually towing a flaming buoy. Even if she became aware of the tell-tale appendage it would be extremely difficult to clear herself, owing to the forward hydroplanes becoming entangled in the wire-netting, before the fast surface ships, waiting in readiness, had spotted the flaming buoy being towed along and were hot in pursuit.
Once entangled in such a net, the submarine's chance of avoiding destruction was small. Not only did the indicator buoy proclaim her every movement to the pursuing surface ships, so that she could not avoid them by turning, sinking to the bottom or doubling in her tracks, but it also enabled depth charges to be literally dropped on her decks.
A considerable measure of success attended the use of this ingenious device until "Fritz" became shy of waters close inshore, and kept a careful look-out for possible lines of indicator nets when forced to pass through narrow channels and waterways. One of the main disadvantages attending the use of these nets was the impossibility of laying them—or, when laid, of hauling them inboard again, during even moderately rough seas. Another difficulty which presented itself when indicator nets were required to be laid in the open sea was the screening of the waiting surface ships from observation. Submarines could not be used on account of their slow speed, and when fast patrol craft cruised about openly within easy range of the nets "Fritz" suspected a trap and steered clear. Even this, however, had its uses.
MINE NETS
It was sought to overcome this difficulty by attaching small explosive mines to the nets instead of indicator floats, so that when a submarine passed through a line she unavoidably struck one or other of the attached mines, which instantly exploded.
This device also proved fairly successful, but the dangers of handling mined nets were considerable and disasters resulted. Furthermore, as such obstructions could not be securely moored in one spot for very long, owing to the action of gales and strong tides, it became necessary for the sake of neutral and allied shipping to maintain a vessel in the vicinity from which warnings could be issued and repairs to the nets effected. This partly defeated the object of mined nets, except for the closing of narrow fair-ways, and their scope as a weapon of attack became strictly limited.
THE MODIFIED SWEEP
This elaborate and costly anti-submarine device was very widely, but not altogether successfully, employed by the auxiliary fleet during the first two years of war. It was nothing more than a long explosive tail towed submerged by a surface ship, the object being to either drag it over a submarine resting on the sea-bed, or else, if the under-water craft was moving, to so manoeuvre the towing surface ship as to swing the tail close to the U-boat, when the heavy charges of T.N.T. attached to the armoured electric cable, forming the tail, would be exploded either by actual contact with the hull of the enemy, or, when sufficiently close to be effective, by the closing of a firing circuit on board the surface ship.
Excellent in theory but very difficult of accomplishment in actual practice. The diagram given will explain the details of this elaborate contrivance, which, however, was soon discarded for more practical methods, although at least one German submarine is known to have been destroyed by it.
LANCE BOMBS
These little engines of destruction were intended for fighting at close quarters, and can be described here in a few lines because of their guileless simplicity. They consisted of conical explosive bombs on the ends of broom handles! A strong man could whirl one of them round his head, like a two-handed sword or battle-axe, and, when the momentum was sufficient, hurl it over the water for about seventy-five feet. On nose-diving into the sea and hitting the hull of a submarine in the act of rising or plunging, the little bomb, containing about 7 lb. of amatol, was exploded by contact.
The damage inflicted on one of the earlier types of submarines by an under-water hand-grenade or lance bomb depended entirely upon what part of the vessel happened to be struck. Their sphere of usefulness was, from the first, very limited, and the advent of the big cruiser submarine, with armoured conning-tower and 5-inch guns, rendered them obsolete.
SMOKE SCREENS
We now come to a more useful device of the purely defensive type employed to screen surface ships from submarine attack. The very simple mechanical and chemical apparatus needed for making the heavy clouds of smoke needs no description beyond that given in the text, but something must be said here regarding the methods of use.
It was not until the third year of the Great War had been ushered in by the unprecedented sinking of Allied merchantmen by German U-boats that the value of the smoke screen as a means of baffling an under-water attack was fully realised. Convoy guards were supplied with the necessary appliances for emitting the fumes with which to cover the movements of the ships under their protection, and so successful was this method of blinding attacking submarines that within a few months thousands of transports, food-ships and warships had been equipped.
When a submarine proclaimed her presence in the vicinity of a convoy either by showing too much of her periscope or by a misdirected torpedo, the guard-ships on the flank attacked immediately dropped their smoke buoys as they continued moving at full speed. By this means an impenetrable optical barrier was interposed between the attacking submarine and the fleet of merchantmen under convoy. When thus shielded from attack—a submarine values her small stock of torpedoes (six to ten) too highly to risk the loss of one or more on something she cannot even see—the mercantile fleet altered course so as to present their sterns to the attacking U-boat, while certain prearranged warships belonging to the escort proceeded to the attack with guns and depth charges.
This means of masking the movements of ships—by no means new in naval warfare—was employed with conspicuous success in the operations of Allied squadrons off Zeebrugge. Individual merchantmen, when attacked by one or more submarines, often threw out a smoke screen to avoid destruction by the big surface guns of the more modern German craft, and its use to cover the movements of transports was very frequently resorted to.
CAMOUFLAGE
The use of camouflage, or the deceptive painting and rigging of ships, came first into being owing to the method employed by submarines for judging the speed of passing surface ships by the white wave thrown off from their bows. It is of the utmost importance for the commander of an under-water warship to correctly judge the speed of the vessel he is about to attack before discharging a torpedo at her. If the estimated speed is too high the torpedo will, in all probability, pass ahead of the moving target, and if it is too low it will run harmlessly astern.
To cause this to happen as frequently as possible, and valuable torpedoes to be wasted—even if the attacking submarine herself could not then be discovered and destroyed—it became advisable to paint imitation white waves on the bows of slow-moving ships in order to give the appearance of speed.
So successful was this simple form of deceptive paint-work that a special camouflage section of the naval service, with an eminent artist as its director, was formed, and all kinds of grotesque designs were painted on the broadsides and superstructures of almost every British merchantman operating in the submarine danger zone.
There was method and meaning in the seemingly haphazard streaks of black, green, blue and white. When looked at from close range only a jumble of colours could at first be seen, but if the distance was increased the effect became instantly apparent. In some cases the deceptive decoration caused big ocean liners to appear small and insignificant. In others it gave the appearance that the vessel was sinking; while quite a favourite ruse was to cause the vessel to appear as if she was travelling in the opposite direction to that which she really was. Two-funnelled ships became single-funnelled, when viewed from a distance or in a dim light, by the simple expedient of painting one funnel black and the other light grey. Liners with tiers of passenger decks had the latter obscured by contrasts of colouring which were really masterpieces of deceptive art. In fact so deceptive became almost every ship in the dim light of dawn and dusk that collisions were often narrowly averted.
It frequently occurred that paint alone was not sufficient to disguise a ship, and woodwork and canvas were resorted to. Big guns were made of drain-pipes and shields of the wood from packing-cases. Cargo boats were given the appearance of cruisers, and cruisers reduced to the appearance of cargo boats. In this way hostile submarines were induced to attack ships, thinking them unarmed and helpless, when in reality they were small floating forts. But at this point simple camouflage ceases and the famous Mystery Ship begins. Before closing this chapter, however, it must be pointed out that camouflage only came into being when the German U-boats commenced their ruthless submarine warfare.
CHAPTER VII
MYSTERY SHIPS
THE "Q" boat, or mystery ship, has been surrounded by so much secrecy that to most people its very being is an unknown quantity. Yet it is to these curious vessels of all sizes and types that the destruction of many hostile submarines was due, and the dangerous work performed by their intrepid crews equalled anything described in sea romance.
The mystery ship was not a specially constructed war vessel, such as a destroyer or cruiser, but merely a merchantman converted into a powerfully armed patrol ship, camouflaged to give the appearance of genuine innocence, but with masked batteries, hulls stuffed with wood to render them almost unsinkable, hidden torpedo tubes, picked gunners, a roving commission and a daring commander and crew. Their work was performed on the broad highways of the sea, and they hunted singly or in pairs, often fighting against overwhelming odds with certain death as the price of failure.
The number of these vessels was not large, possibly 180, but their operations extended far and wide. They roamed the North Sea, the Atlantic, the English Channel, the Mediterranean, the Arctic Ocean and even the Baltic, but until challenged were quite unknown to all other vessels of the Allied navies. Theirs was a secret service, performed amidst great hardships, with no popular applause to spur them on.
As all "Q" boats—as they were officially called—differed from each other in size and armament, any description given here can only be taken as applying to one or more vessels with which the writer was personally familiar. Some of these so-called mystery ships were old sailing schooners, others fine steamships, while quite a number were converted fishing smacks, drifters and trawlers, the method being to give the prospective commander a free hand in the conversion of his ship from a peaceable merchantman to a camouflaged man-of-war, and many were the ingenious devices used.
One vessel fitted out for this desperate duty at a Scottish base was a steamer of about 400 tons burden. She was armed with a 4.7 quick-firing gun hidden in a deck-house with imitation glass windows, the sides of which could be dropped flat on to the deck for the gun to be trained outboard by simply pressing an electric button on the steamer's bridge. Two life-boats, one on each side of the aft deck, were bottomless, and formed covers for two additional 12-pounder guns. A false deck in the bow shielded a pair of wicked-looking torpedo tubes, each containing an 18-inch Whitehead ready for launching; and the crew for each gun were able to reach their respective weapons, without appearing on deck, by means of specially constructed gangways and hatches. The very act of dropping the sides of the aft gun-house hoisted the White Ensign, and technically converted this unsuspicious-looking merchantman, which asked only to be allowed to pursue its lawful vocation on the high seas, into a heavily armed warship.
This "Q" boat had, when met and challenged by the writer's ship, already accounted for no less than three German submarines which had opened the attack from close range, thinking her defenceless.
Another smaller mystery ship was a converted fishing drifter with a single 12-pounder gun on a specially strengthened platform fitted in the fish-hold, which had been cleaned, matchboarded and painted to provide accommodation for the crew of picked gunners. This little ship had no torpedo tubes and the muzzle of her gun was hidden beneath fishing nets.
There were, however, some very large and elaborately fitted "Q" boats. These had specially constructed torpedo tubes low down in the hull, masked 4.7-inch guns in more than one position, special chutes for depth charges, coal bunkers arranged round the vital machinery to protect it from shell-fire, and, moreover, were filled with wood to make them almost unsinkable even if torpedoed.
Each such vessel was provided with a "panic party," whose duty was to rush to the life-boats when the ship was attacked by a submarine. This gave the final touch to the disguise, and often induced the submarine to save further torpedoes by coming to the surface and continuing the assault with gun-fire.
The story of the sinking of the last German submarine in the war by the "Q 19" will give some idea of how these vessels worked. It occurred in the Straits of Gibraltar, about twenty-four hours before the signing of the Armistice. The Q 19 was waiting in the Straits expecting to intercept three big U-boats on their way back to Heligoland. About midnight the first of these craft came along, and sighting the innocent-looking "Q" boat prepared to attack her with gun-fire. For nearly an hour the mystery ship "played" the submarine by pretending to make frantic efforts to escape, but all the time allowing the under-water craft to draw closer and closer.
The "Q" boat was under a heavy fire from the submarine, one shell wounding eleven out of the crew of sixty, another carrying away the mast and a portion of the funnel, but no sign of a gun was yet displayed on board the surface ship. This withholding of fire until the last moment, when the range has become short and the effect certain, is one of the great nerve tests imposed on the crews of all mystery ships. It is an essential of success, for a few wild shots at long range would disclose the fact that the vessel was heavily armed, and the attacking submarine would either sheer off or else submerge and use her torpedoes.
When the chase had been on for about fifty minutes, and the submarine was only 200 yards astern, the "panic party" in the "Q" boat rushed for the life-boats. The shells were now doing serious damage to both hull and upper works, and the submarine was creeping close to give the coup de grace.
At this, the psychological moment, the order to open fire was given. The collapsible deck-house, shielding the 4.7 gun, fell away on its hinges. Eleven shots were fired in quick succession, all of which struck the submarine. One blew the commander off the conning-tower and another rent a gaping hole in the vessel's hull. In less than fifteen minutes the fight was over and the last U-boat to be sunk in the Great War of civilisation had disappeared beneath the waters of the Straits of Gibraltar.[4]
FOOTNOTE:
[4] One of the remaining U-boats afterwards succeeded in torpedoing the battleship Britannia.
CHAPTER VIII
A TYPICAL WAR BASE
THE last few chapters have dealt mainly with the weapons used in anti-submarine warfare. We now come to the naval bases on which the fleets armed with these curious devices were stationed for active operations.
Around the coasts of the British Isles there were about forty of these war bases, each with its own patrol flotillas, minesweeping units and hunting squadrons. The harbours, breakwaters and docks had to be furnished with stores, workshops, wireless stations, quarters for officers and men, searchlights, oil-storage tanks, coal bunkers, magazines, fire equipment, guard-rooms, signal stations, hospitals, pay offices, dry docks, intelligence centres and all the vitally necessary stores, machinery and equipment of small dockyards.
To do this in the shortest possible time, and to maintain the supplies of such rapidly consumed materials as oil fuel, coal, food, paint, rope and shells for perhaps a hundred ships for an indefinite number of years, it was often necessary to lay down metals and sidings to connect the base with the nearest railway system. At many bases secure moorings had also to be laid by divers, and the channels and fair-ways dredged. The larger bases also required temporary shore defences, and booms arranged across the harbour entrances to prevent hostile under-water attacks.
Then came the problem of finding the personnel. The ships had already been provided for, but to keep them in fighting condition, and for the work of administration, it was necessary to have a shore navy behind the sea-going units. An admiral from the active or retired list was appointed to each base as the "Senior Naval Officer." Then came additions to his staff in the persons of executive and engineer commanders, officers of the Reserve, chaplains, surgeons and paymasters. With these departmental chiefs came their respective staffs of warrant officers, petty officers, wireless operators, engine-room artificers, motor mechanics, shipwrights, carpenters, smiths, naval police, signalmen, storekeepers, sick berth attendants and parties of seamen. Finally, a generous supply of printed forms and train-loads of stores.
This then, in brief outline, was the material which went to form the war bases of the auxiliary, or anti-submarine, fleets. In many cases much more was required, especially at such important depots as Dover, Granton and Queenstown. About the permanent dockyards, like Portsmouth, Devonport and Rosyth, or the Grand Fleet bases, nothing need be said here, because they do not come within the scope of this book. The same may also be said of that desolate but wonderful natural anchorage, Scapa Flow, the headquarters of the Grand Fleet in the misty north. Each of these mammoth naval bases had an auxiliary base for anti-submarine and minesweeping divisions.
With a knowledge of these essentials a more detailed description of a typical war base and the work of its staff may prove of interest. Taking as an example a large depot, supplying all the needs of over a hundred erstwhile warships, and situated in the centre of the danger zone, we find a central stone pier on which has been erected a perfect maze of wood and corrugated iron buildings, with the tall antennae of a wireless station, a little look-out tower and a gigantic signal mast from which a line of coloured flags is aflutter in the sea breeze. The shore end of the pier is shut off from prying eyes by a lofty wooden palisade with big gates, in one of which is a small wicket. Outside a sentry with fixed bayonet paces to and fro.
The first person inside the sacred precincts to greet the stranger is a keen-eyed "Petty Officer of the Guard." When the credentials have been examined the visitor is sent under the guidance of a bluejacket to the "Officer of the Day," whose "cabin" is inside the maze of corrugated iron and weather-board. The doors flanking the passages traversed display cryptic lettering, such as I.O. (Intelligence Office), S.R. (Signal Room), S.N.O. (Senior Naval Officer), "Commander" (usually the second in command of the base), P.M.S.O. (Port Minesweeping Officer), C.B.O. (Confidential Book Office), M.L.Com. (Motor Launch Commander), O.O.W. (Officer of the Watch), "Officers only" (the wardroom and gunroom combined), and, finally, the O.O.D., or the abode of that much-worried individual, the Officer of the Day, whose duties happily terminate when his twenty-four hours of administrative responsibility are over, only, however, to return in strict rotation.
[Illustration: FIG. 17.—The central pier of a typical anti-submarine naval base. 1. Wardroom. 2. Sec. to senior naval officer. 3. Admiral's cabin (S.N.O.). 4. Flag commander (or lieutenant). 5. Base intelligence office. 6. Base commander. 7. Chaplain and gift store. 8. Drafting officer. 9. Store officer. 10. Chart-issuing office. 11. Cabin of the officer of the day. 12. Telephone exchange. 13. Warrant officers. 14. Pay office. 15. Fleet paymaster. 16. Paymasters and asst.-paymasters. 17. Writers and W.R.N.S. 18. Engineer-commander's office. 19. Men's quarters (for base duties and reserve). 20. Men's recreation room. 21. Petty officers. 22. Men's mess-room and adjoining galley. 23. Sick-bay. 24. Fleet surgeon. 25. Baths. 26. Baths. 27. Stores. 28. Boom defence office. 29. King's harbour master. 30. Hull defects office. 31. Police and cells. 32. Coaling office. 33. Wireless cabin. 34. Guard room. 35. Railway platform. 36. Sentry box. 37. Cranes. 38. Berths for armed yachts in harbour. 39. Motor launches in harbour. 40. Drifters. 41. Patrol trawlers. 42. Minesweepers. 43. Whalers. 44. Coastal motor boats. Larger ships, such as sloops, destroyers, "P" boats, coaling and ammunition hulks, lying out in basin.]
Again comes an apologetic examination of credentials, possibly followed by a few minutes with the admiral commanding, and then the grand tour commences. First come the ships lying alongside the stone pier, with their short funnels belching black and very sooty smoke. These are the "stand-off" units, whose crews are enjoying a brief few hours ashore after days or weeks out on the dangerous seas beyond. Big drums of oil are being lowered by ropes on to their decks. The sound of hammering comes from more than one engine-room, where machinery is being overhauled. On the decks of several, men with little or no resemblance to the clean "Jacks" of the naval review are fondly polishing, painting or greasing the long grey barrels, steel breech mechanism, or the yellow metal training wheels of guns. Others are cleaning rifles, which have recently been used with special bullets for sinking floating mines. One ship is washing down decks after coming in late from night patrol; another is receiving its three-monthly coat of grey paint; while on to the deck of a whaler—black and ominous-looking—hundredweights of provisions in boxes and bags are being lowered from the quay.
Astern of these lie two tiers of light grey spick and span motor launches, their decks spotlessly white, and their small canvas and glass screened wheel-houses ill concealing polished brass indicators, Morse signalling key, electric switches, binnacles and other paraphernalia. Behind these lie the 40-knot coastal motor boats, like miniature submarines, with torpedoes in cavities in their aft decks, and little glass-sheltered steering-wells. Further towards the head of the pier is a line of big flat Scotch motor drifters, built for rough weather with 9-inch timbers, their decks a maze of wire nets, glass floats and brick-red chemical canisters.
On the opposite side of the pier, in front of the S.N.O.'s cabin, lies a big grey yacht with four 12-pounder guns and an anti-aircraft weapon pointing over the sky-reflecting water. Lying out in the basin are big minesweepers, looking more like pre-war third-class cruisers, two slim-looking dark grey destroyers, a dredger and a few nondescript craft.
Inside the first row of iron sheds are stores, with barrels of tar, drums of paint, immense coils of rope and a naval "William Whiteley's"—in which anything from a looking-glass to a ball of string, or a razor to a dish-cloth, can be obtained in exchange for a signed form from the Naval Store Officer, whose cabin near by is a maze of similar forms of all colours.
Then a worried-looking man hurries by and the O.O.D. smiles. "He's the coaling officer, and there's some twenty ships waiting to get alongside to take the beastly stuff aboard," is the laconic explanation.
A cabin marked I.O. is entered—every room is a cabin in a naval base. Here the walls are decorated with innumerable charts with mysterious red lines. A curious device, with the names of all the ships belonging to the base painted on wooden slides, reaches across one side. It is the indicator which shows at a glance the ships at sea and those in harbour, the names of those under repair, the unit to which each vessel belongs and when she goes out or comes in for "stand-off."
This is the Intelligence Office, and signals and wireless messages from the patrols and battle fleets are being almost continuously brought in and carried out by messengers. The Commanding Officer (C.O.) of a minesweeper is making inquiries about tides and the exact position on the chart of a newly located mine-field. Another officer is locking a black patent-leather dispatch-case—he is the King's Messenger or, more correctly, the "Admiralty Dispatch Bearer," who carries to and from London and the fleets all the secret correspondence and memoranda of the Naval War Staff and other important departments. A big safe in the corner of the cabin contains the secret codes and ciphers used when transmitting messages, and two overworked officers are busy at near-by desks translating signals to and from "plain English."
The next cabin contains the admiral's secretary and his staff of writers. Here a flotilla commander is receiving his "sailing orders," without which no ship proceeds on a voyage. Adjoining this is the Pay Office, in which, with the exception of a newly joined recruit mortgaging his pay for two weeks ahead—he knows that he will be at sea for that time—there is a decided air of quietude. The rush in this abode of paymasters comes at the end of each month, when all the officers arrive in a body to demand the meagre fruits of their labours.
Sandwiched between the clean and varnished cabin of the Base Commander, who is "taking" defaulters, and the camp-bedded apartment of the O.O.W. is a most interesting little combined cabin and store, presided over by the Chaplain. Here are piles of woollen socks, cardigans, balaclavas, mitts and other clothes knitted by the thoughtful women of the Empire for their sailor sons. Here seamen are estimating the cold-resisting qualities of different garments—for winter in the North Sea is the next thing to Arctic exploration. Officers are popping in and out to borrow a pile of books—thrice blessed were the senders of these donations. The corner of the cabin is piled with fresh vegetables, but alas! the cry is apples! No exhortations to righteousness adorn the walls, and the chaplain is joking with a big stoker who is distractedly turning over the cardigans in search for one large enough to encompass his massive frame. A signal boy slips in, gets chocolate, gives a breathless thanks and slips out just in time to avoid the playfully raised hand of the P.O. of his ship. Two deck hands, covered in coal dust, put their heads round the door to ask if they can have a bath, and the indefatigable chaplain hands them the keys of the room provided for the purpose by the generous.
Religion here is more practical than theoretical. If a man swears when the "Padre" is present he pays a small fine, which goes to the recreation or other needy fund. The Commander is not immune from this law at the base under review, and has more than once been "heavily fined" for giving his true opinion of German sailors and winter weather.
The next cabin is that of the O.O.W., a seething mass of officers demanding "duty boats" and pinnaces to convey them to and from their ships lying out in the fair-way. Others are expostulating about being ordered to sea during their "stand-off," informing everyone what a rotten service the navy is, crossing-sweeping is a sinecure compared with it. Then a few pass on to the cabin near the men's quarters. Here the "Drafting Officer" is trying to palm off a deck hand on the C.O. of a trawler, who is vainly explaining that he must have a signalman. A telephone rings and news comes from the "Sick Bay" that an engineer has been badly burned and will be unable to go to sea with his ship. The distracted drafting officer searches through his lists of reserves for some competent man to take the place of the casualty.
Peace reigns in the adjoining department, where a grey-haired veteran is issuing charts, "Sailing Directions," "Tide Tables" and "Warnings to Mariners." In the near-by engineer-commander's office worried experts are wrestling with innumerable problems relating to M.L. motors, steam capstans, steam steering gear, electric dynamos, damaged propellers, broken shafts, boiler cleaning and the numerous imperfections of overworked ships' engines.
The Boom Defence staff is placidly serene. The turn of this department comes after a heavy gale has damaged the submarine nets, chains and buoys. The torpedo officers and their "parties" are discussing the best way of moving four of these steel monsters from a neighbouring depot ship to a new "Q" boat with only a rowing-boat at their disposal—soon the O.O.W. will be called upon to supply a drifter for the purpose.
In the ordnance store a veteran P.O. is trying to make his list of returned brass shell-cases correspond with the number of shells supplied to various ships six months before. He knows the sailors' fondness for shell-cases as ornaments in their little far-away homes, and, failing to make all the figures agree, decides that some must have been "washed overboard."
The Port Minesweeping Officer is discussing with his sea commanders the clearing of a new mine-field laid by U-C-boats within the past few days, when a sudden stir is caused by the arrival of a signal from the wireless room to the effect that one of his vessels has struck a mine in lat. —— long. —— and is sinking. He appeals by telephone to the M.L. commander and in less than ten minutes a flotilla of fast launches is racing at 19 knots to the rescue.
In the Admiral's cabin there is to be a conference of senior officers later in the day to decide on the best means of ridding the seas within that area—and each base has its own area of sea—of a hostile submarine which has been inflicting undue loss upon shipping, its latest victim being a Danish barque.
The combined wardroom and gunroom has some twenty occupants, reading the newspapers and magazines, warming themselves before the two big fires, or talking in little groups. This base has suffered some heavy losses lately, but reference to those "gone aloft" is seldom made, except quietly and a little awkwardly. The talk is of theatres in neighbouring towns, the respective merits of certain types of ships and weapons, the prospects of early leave, the dirty warfare of "Fritz" or the "beauties" of the North Sea in winter.
In this room all questions of rank and precedence are more or less waived. There are, of course, differences, especially when the wardroom, or abode of senior officers, does duty also as a gunroom for the juniors. But here there is camaraderie and an absence of iron discipline, although a sub-lieutenant would be extremely ill advised either to drop the prefix "Sir" or to slap the Commander on the back in an excess of joviality, relying on "neutral territory" to save him from rebuke. It is, however, no uncommon event to see all ranks of officers engaged in a heated debate, or groups of juniors laughing round the fire while their elders are vainly trying to concentrate their minds on the latest Press dispatches. Games are played and glasses clink merrily, but in a gunroom there is a very strict limit as to both time and quantity, though none regarding volume or discordance of sound.
* * * * *
Passing on to the organisation of the flotillas for sea, we find in this large base six minesweeping units, two being composed of fast paddle sweepers and four of trawlers. The former are used for distant operations and comprise nine vessels. They work in pairs, but the extra ship is available to sink mines cut up by the sweeps of the others, and to be immediately ready to beat off submarine attacks.
The trawlers are engaged in sweeping daily the approaches to the harbour and a recognised channel up and down the coast. Their work overlaps with that done by the ships belonging to the neighbouring bases. In this way the "war channel," about which more will be said later, was kept free of mines, and afforded a safe route for ships from the Thames to the Tyne, and in reality to the northernmost limit of Scotland.
This important duty was seldom left unperformed even for a day, except during fierce gales. Often the discovery of a distant mine-field caused many ships to be concentrated on clearing it, and the number available for the "routine sweeps" was consequently reduced, but longer hours of this arduous and dangerous work made up the difference, and the work went on in summer fog and winter snow for over four years.
The anti-submarine patrols were composed of five ships each, under the command of the senior officer of the unit—frequently a lieutenant with the responsibility of a captain. Their work lay out on the wastes of sea lying between England and Germany. It was seldom that the whole five vessels of each unit cruised together, the usual method being to scatter over the different "beats" and rendezvous in a given latitude and longitude at a specified time and date. They were usually able to communicate with each other and with the base on important matters by wireless. Their periods at sea varied from ten days to three weeks, with a four days' "stand off" when they came into harbour. But of this time one day at least was spent in coaling and provisioning the ship ready for the next patrol. This ceaseless vigilance on the grey-green seas of England's frontier was seldom interrupted for more than a few days in the year by impossible gales. Anything short of literally mountainous seas did not prevent the trawler patrols from riding out the storm carefully battened down and with just sufficient speed to keep head to sea.
The drifters were divided into patrol units, boom defence flotillas and under-water or mine-net units. Their work was thus more varied but equally as arduous and risky, as the loss of 30 per cent. of the entire fleet of over 1000 ships affords undeniable proof. The periods of sea duty were similar to those of the trawlers.
The motor launches at each base had some hundred square miles of sea to guard, and hunted in fives. The rough weather these plucky little ships endured in the open sea in mid-winter, the intense cold—for there was no proper heating appliance—and the state of perpetual wetness made their duties among the most arduous in the sea war. Later pages of true narrative will show to the full the work of these gnats of the sea.
In addition to all these flotillas there were convoy ships, whaler patrols, "Q" boats and a number of special duty ships. The work of the former was of the most exacting character, and left the crews of these vessels but little time ashore. In the base under review so arduous were the duties of the convoy ships that it became a matter of self-congratulation for patrol and sweeper officers and men that their ships were not so employed, and this by men who sailed submarine and mine infested seas for an average of 270 days in each year!
It must not be assumed that when in harbour there were no duties to be performed by either officers or men of sea-going ships. They had, on the contrary, to furnish anchor watches, shore sentries, duty crews for emergency pickets, prisoner guards, working and church parties, to attend drills, rifle practice, gun practice and instructional parades. The officers had similar shore duties to perform, which left them little time to rest from the strain of keeping watch and ward on the death-strewn seas.
CHAPTER IX
THE CONVOY SYSTEM
ALTHOUGH the convoy system was employed at the beginning of the war for the transport of the Imperial armies to France, and subsequently for all the Allied troop movements overseas, it was some three years later before it was extended to the entire British Mercantile navy, on which the United Kingdom depended for too many of the necessities of civilised life.
The rapid development of submarine piracy, however, compelled the Admiralty, early in the year 1917, to resort to what was merely a new form of the old system of protecting sea-borne trade. This comprised the collection of all merchant ships passing through the danger zones into nondescript fleets, and the provision of light cruisers, destroyers, torpedo-boats, trawlers and occasionally (for coastal convoys) of patrol launches to escort them. Certain types of aircraft were also frequently used for observation and scouting purposes.
Previous to the adoption of the convoy system a merchantman, whether it was a fast-moving liner or a sturdy but slow ocean tramp, zigzagged through the danger zones with lights out and life-boats ready. Many were the exciting runs made in this way, with shells ploughing up the water around and torpedoes avoided only by the quick use of the helm; but the courage of our merchant seamen was of that indomitable character exhibited now for over three centuries, since the days of Drake, Hawkins, Raleigh and the other sea-dogs of old.
But the danger zones grew wider as the radius of action of newer and larger German submarines increased. At last no waters were immune, from the Arctic circle to the Equator, or from Heligoland to New York.
The hour was one of extreme peril for the sea-divided Empire. To lose several hundred ships, with many thousands of lives and much-needed cargoes of food and munitions, when the valiant armies of civilisation were battling with the Teuton hordes, was bad enough; but if the enemy had been able, by casting aside the laws of humanity and sea war, to compel British ships to remain in harbour or meet certain destruction on the high seas, the result could only have been the complete failure of the Allied cause, the conquest of Europe and the fall of the greatest political edifice since Imperial Rome.
Between the world and these catastrophes, however, stood the undefeated Mercantile Marine and the Allied navies. Councils were held in the historic rooms of Whitehall and the old convoy system emerged from the archives of Nelson's day. The commerce raiders were no longer the canvas-pressed privateers of the sixteenth, seventeenth and early eighteenth centuries, who fought a clean fight, often against great odds, but were submarine pirates of the mechanical age, who only appeared from the sea depths when their victims had been placed hors de combat.
It is an old axiom of war that new weapons of attack are invariably met by new methods of defence. So it was with the convoy system which gave the death-blow to German hopes of a submarine victory. In order to understand this new method it is necessary to study the accompanying diagram, which, however simple it may appear on paper, is extremely difficult to carry out in practice.
At each great port there was a convoy officer, who assembled the merchant ships when they had been loaded and explained to their captains the exact position each ship was to occupy when the fleet was at sea. Printed instructions were handed round urging each vessel to keep its correct station, stating the procedure to be adopted in the event of an engine breakdown, giving the manoeuvres which were instantly to be carried into effect when an attack was threatened, and finally the special signals arranged for communication between the merchantmen and their escort by day and by night.
The number of vessels composing a convoy varied, but often exceeded twenty big cargo ships, carrying some 120,000 tons of merchandise, or six liners, with 20,000 troops on board, while the escorting flotilla consisted of a light cruiser, acting as flag-ship, six destroyers, two special vessels ("P" boats) towing observation airships, and some eight or ten trawlers, with possibly one or more seaplanes and several M.L.'s for the first few miles of the voyage. The destroyers were spread out ahead and on the flanks of the fleet, and by using their greatly superior speed were able to zigzag and circle round the whole convoy.
In the event of an attack the whole fleet turned off from the course they were steering at a sharp angle, showing only their sterns to the U-boat. A destroyer acted as rearguard to prevent any of the convoyed ships from straggling. When the fleet had arrived at a rendezvous far out in the open sea, where the danger of a submarine attack was much less, the escort handed over their charges to one or two ocean-going cruisers, which stayed with the merchant ships throughout the remainder of their voyage.
The escorting flotilla then cruised about in the vicinity of the rendezvous until an incoming convoy appeared. These ships were then taken over from their mid-ocean cruiser guard and escorted back through the danger zone to port, and so the game of war continued until months became years.
All this may sound straightforward and quite simple, but there were difficulties, to say nothing of dangers, which made it a most arduous operation. First came the speed problem. Every merchant ship differed in this important respect, so the speed of the slowest unit became the speed of the entire fleet, and this reduction made an attack by under-water craft much easier of accomplishment. Hence the call for "standard ships," which is a point that should be borne in mind by future generations as a safeguard against blockade. Then came the question of destination, which increased the number of escorting flotillas, and especially ocean cruiser guards, required for a given number of cargo ships. Next there was the loading and unloading to be considered, involving long hours and hard work by the men on the quaysides. This great difficulty was one of the reasons for the formation of docker battalions. Coaling such big fleets by given times caused many grey hairs to appear where otherwise they would not have been. Finally there was the danger of mines having been laid in the fair-ways leading to the port, which necessitated every convoy being met by special vessels to sweep the seas in front of each incoming and outgoing fleet.
All this and more had to be contended with and overcome before each convoy was able to sail. Then danger and difficulty came hand-in-hand. On a bright morning, with probably a fresh breeze blowing and a choppy sea, the work of the escorting flotilla was easy, but with such climatic conditions the risk of attack was so great in the waters around the coasts that troopships usually left harbour under cover of night. No lights were then allowed, and it will not be difficult for readers to imagine what it meant to be pounding through a black void in a fast-moving destroyer, against, possibly, a heavy head sea, with some twenty or thirty big ships in the darkness and spray around. Thick sea-mists were the cause of endless trouble, for the safety of an invisible fleet depended on the vigilance of a half-blind escort. Winter gales scattered the ships and rendered signals invisible. Attacks came from the most unexpected quarters and often from more than one point of the compass at the same time. However, relief came at last, on that never-to-be-forgotten morning when Sir David Beatty and his admirals accepted the unconditional surrender of the German fleet and its unsunk submarines.
Were this chapter to end with the foregoing description of the convoy system the reader would not be in possession of the full facts from which to gauge the importance of the work. Something must be said of what was accomplished. First in order of importance came the transport of many millions of soldiers not only from England to France, but also to and from every colony and dominion of the world-wide Empire. By August, 1915, the British navy had transported, across seas infested with submarines and mines, a million men without the loss of a single life or a single troopship.[5] The first Canadian army of 33,000 men crossed the Atlantic in one big fleet of forty liners, under the escort of four cruisers and a battleship, in October, 1914, without accident. Transports to the number of 60 were required to convey the first Australian army over the 14,000 miles of sea to Europe, and it was while convoying this huge fleet that the cruiser Sydney chased and destroyed the German raider Emden. The Russian force which rendered valuable service in France was safely convoyed over the 9000 miles of sea from Dalny to Marseilles. Never once during the four and a half years of war was the supply of food, munitions and reinforcements, or the return of the wounded—to and from the many theatres of land operations—seriously hindered by the German, Austrian or Turkish navies.
Turning to the gigantic task of guarding England's food supply, we find, in one notable case, an example of the good work performed almost daily for nearly five years. Over 4500 merchant ships had been escorted across the North Sea to Scandinavian ports alone before the disaster of 14th October 1917 befell the convoy on that route. On that occasion the anti-submarine escort of three destroyers were intercepted, midway between the Shetland Islands and Norway, by two heavily armed German cruisers. The destroyers fought to the last to save their charges, but unfortunately only three merchant ships succeeded in getting safely away. Five Norwegian ships, three Swedish and one Danish ship were sunk. From this it will be observed that not only British merchantmen were protected by escorts.
The second attack on the Scandinavian convoy occurred on 12th December. The escort consisted of two destroyers, the Partridge and Pellew, with four armed trawlers. Fortunately the convoy was comparatively a small one, for it was attacked and almost totally destroyed in the North Sea by four of the largest German destroyers. H.M.S. Pellew, although badly damaged, succeeded in returning to England.
It may be rightly thought that in both these cases the escorting flotilla was not strong enough, but it should be remembered that if heavier ships had been employed they would have been much less able to cope with a submarine attack. The escort in both cases was purely an anti-submarine defence, and only on the Scandinavian and Netherlands routes was a surface attack at all possible, because all exits from the North Sea were securely closed by the strategic positions occupied by the Grand Fleet and the battle cruiser squadrons, in conjunction with subsidiary fleets at Harwich and extensive mine-fields.
When it became apparent that surface as well as submarine attacks on the North Sea convoys had to be provided against, other means were promptly adopted, and no further disasters occurred.
The strong escort accompanying the transports bringing to Europe the first American army were attacked at night by a submarine, but succeeded in avoiding the torpedoes fired. This was due to the smartness with which the United States warships were manoeuvred. Three subsequent attacks on the same convoy route also failed.
The Report of the War Cabinet for the year 1917 gives some remarkable figures in support of the convoy system. On the Atlantic routes about 90 per cent. of the ships were formed into fleets and escorted. From the inauguration of this system the loss on these routes from all causes was 0.82 per cent., and if all the trade routes to and from the United Kingdom are included, the loss was only 0.58 per cent. With these figures in mind, who will deny that the navy is the surest form of national as well as Imperial insurance?
FOOTNOTE:
[5] When writing of the navy in this connection due praise should be given to the Mercantile Marine, which this war has proved to be a very important part of the true sea power of Great Britain.
CHAPTER X
THE MYSTERIES OF SUBMARINE HUNTING EXPLAINED
WHEN all is said and done, anti-submarine warfare is very like big-game hunting. Success depends entirely on the initiative, skill and resource of the individual hunter. Contrary to general belief, there is, at present, no sovereign remedy for the depredations of under-water craft with their torpedoes and mines. There are, however, several recognised methods of attack and defence employed by surface ships in this newest form of naval warfare.
When the new navy took the seas in 1914-1915, bases were established not only round the coasts of the British Isles, but also in the more distant seas. The principal danger zones were, however, the North Sea, the English Channel, the Irish Sea, the Mediterranean and the eastern portion of the North Atlantic. It was through these waters that every hostile submarine must pass on its voyage out and home.
This geographical factor restricted the theatre of major operations to some 180,000 square miles of sea. Minor offensive measures might have to be adopted against individual U-boats cruising at long distances from their bases, as actually occurred off the United States coast, but the fact of Germany possessing large submarine bases only along her own North Sea coast, and temporary ones on the Flanders littoral, enabled a concentration of Allied anti-submarine craft to be made in the narrow seas which afforded the only means of entry and exit to and from those bases.
The same may be said of Austria in the Adriatic and of Turkey behind the Dardanelles.
This favourable combination of circumstances would not occur if (however unthinkable) England, France or the United States were ever to wage a rigorous war against shipping. The large number of oversea naval bases possessed by these Powers would cause every sea to become a danger zone within a few hours of the commencement of hostilities. No effective concentration of hostile surface craft would be possible with the zone of operations spread over the water surface of the entire globe, and if the bases themselves were secured by predominant battle fleets, or numbers of heavily armed monitors, the seas would quickly become impossible for purposes of hostile transport.
This geographical restriction of the German and Austrian danger zones made effective concentration of the Allied anti-submarine fleets and their devices possible. The 180,000 square miles of sea, forming the theatre of major operations, was, on special charts, divided into areas, comprising a few hundred square miles of sea. Each area was given a distinctive number, and a base was established for its own patrol and minesweeping fleet.
The areas themselves were again subdivided on special charts into squares or sections. Each square covered a few leagues of sea and was known by an alphabetical sign. In this way the waters of the submarine danger zone were divided into areas, with their bases and protective fleets, and squares with their respective squadrons or ships.
Each square of sea was covered once or twice daily by its own patrol ship or flotilla. Where the danger was less the patrol was not so frequent and the squares were almost indefinite in size, but where the chances of successful operations were exceptional, as in the Straits of Dover, additional offensive measures were employed (see under Mine Barrages).
This, then, was the chess-board on which the game of submarine warfare was played. To facilitate communication between the different patrols spread over the squares of sea, wireless was fitted in many ships, and war signal stations were erected on prominent points of land. Each base was able to communicate by wireless with any of its ships out on patrol duty, and was also connected by land-line telegraph, telephone and wireless with naval centres.
These latter were head intelligence offices, usually situated at the great bases of the battle fleets. In this way any concentration of hostile surface warships noticed by the patrols (sometimes submarines were employed, especially in the Heligoland Bight) could be communicated in a few minutes to the admirals commanding the Grand Fleet, the Battle Cruiser Squadron or other large fighting organisations.
At the naval centres the movements of hostile submarines were recorded on charts. If, for example, it was reported from a patrol boat that the U16 had torpedoed a ship in square "C," area 41, at 10 A.M. (G.M.T.[6]) on 4th August, and the patrol had arrived on the scene too late to be of any service, a warning could be wirelessed to hundreds of vessels on the seas surrounding the scene of outrage to keep a careful look-out for the U16.
[Illustration: FIG. 21.—Diagram showing how an area is covered by patrols. A. Unit or flotilla of ships may proceed out from the base on course indicated by arrows B, which would be called the "Northern Inner Beat," and return to harbour on course A, "Northern Outer Beat." Other units of ships would simultaneously follow the course E. These and adjacent squares of sea would be covered daily by one or more ships of each unit. The southern half of the area would be patrolled in the same way. The "Outer Beat" is shown by the arrows C, and the "Inner Beat" by the arrows D. The points +F show the possible positions of armed patrols acting independently of any unit or flotilla.]
Subsequently a further message might come to the naval centre that the same submarine had been chasing a merchantman in square "D," "E" or "F" in the adjoining area. A concentration of fast ships, such as destroyers, M.L.'s or coastal motor boats, could then be made so as to intercept the raider or enclose her in a circle while other vessels hunted her down.
In a like manner important convoys coming down the coast, or entering a danger zone from the open sea, could be met by a local flotilla and escorted to a rendezvous with a flotilla from the adjoining area. In this way they were passed through the submarine and mine infested seas to and from their harbour terminus.
Almost the same methods were employed in dealing with the thousands of German mines. But to describe that part of anti-submarine warfare here would be to encroach on the subject of a succeeding chapter.
PATROLS
The method of patrolling the areas and squares of sea was comparatively simple, though the same cannot be said of the actual work. The lines of patrol were called "beats," and there was usually an "inner" and an "outer" beat for each unit or flotilla of ships. If when a ship (or a unit) reached her allotted square, from which the line of patrol extended, she elected to proceed on the inner beat, she would generally accomplish the return journey to the point of departure on the outer beat, thus covering her respective zone of patrol, but leaving the exact route to the discretion of the commanding officer. In this way no hostile submarine with a knowledge of the system could be sure of when or where a patrol ship would be met. In the same way it was left to the commander of a flotilla to either divide his ships into pairs, single units, or to maintain them as a homogeneous fleet, so that any combination of hostile submarines could not be made which would be sure of being able to attack a single patrol. Such an enemy combination might encounter a single ship, but it might also walk into the arms of a whole flotilla; or it might attack a single ship only to find itself surrounded by a following fleet.
[Illustration: FIG. 22.—Diagram illustrating the operations of a hydrophone flotilla composed of armed motor launches. Each vessel is given a number, and the flotilla proceeds in line-abreast along the course shown by the dotted lines. Each vessel is one mile from the other, and the whole line stops by signal at the point marked with a cross. Hydrophones are put in operation, and after a period of listening the flotilla continues on its course, as no submarine sounds are heard. The flotilla turns to head south, and a stop is again made to listen on the hydrophones. This time the sound of a hostile submarine is heard by vessel No. 1, bearing S.W. This report is confirmed by vessel No. 2 hearing the same sound, bearing a few degrees farther W. The two bearings A and B are then drawn on a chart, and the point where the two lines cross is the approximate position of the invisible submarine. The attack with depth charges is then ordered.]
The beats which were most distant from the base were given to the largest ships. This was done because it was often impossible for the more distant patrols to reach a place of shelter before one of the fierce gales which swept the northern seas was upon them. Trawlers, large steam yachts and converted merchantmen were usually employed on squares more than one hundred miles distant from a harbour of refuge, while motor launches kept watch and ward on the seas closer inshore.
The duration of patrols varied according to their position. Some lasted three weeks and others only a few days or hours. When the ships returned to their base after a spell at sea they were given a corresponding "rest" in harbour. A three weeks' patrol meant several days' "stand-off," while a two or three days' patrol entitled the ship to twenty-four hours in the comparative comfort of a harbour.
It must not be imagined, however, that a stand-off meant entire idleness or thorough rest. There were duties to perform which robbed it of much that it was intended to give. Ships had to be coaled, provisioned, painted or repaired. Engines had to be overhauled, sentries posted ashore, a guard to be furnished, and every day one ship in each unit that was in harbour had to be manned and in readiness for emergencies.
HYDROPHONE FLOTILLAS
We now come to the actual methods employed by surface craft when attacking submarines. Although, as previously stated, much was left to individual initiative, there were, nevertheless, certain recognised methods.
Taking as an example the operations of a hydrophone flotilla of armed motor launches, the number of vessels forming the unit was usually five. When out scouting for the enemy they proceeded in line-abreast for about one sea mile, then stopped their engines and listened on their hydrophones for the noise of a submarine cruising in the vicinity. If nothing was heard the mile-long line of miniature warships advanced another mile and again stopped to listen. This manoeuvre was repeated until one or other of the ships heard the familiar sound of a U-boat. Nothing might be visible on the surface of the sea, but if this was the case and the noise came up from the ocean depths over the electrified wires of the detector, it was conclusive proof that a submarine was in the near vicinity.
The M.L. first detecting the noise hoisted a signal (flag by day and coloured electric light by night), giving the direction from which the sound came (see Fig. 22). The next ship in the line to receive the sound on its instruments then hoisted a signal, also giving the bearing—i.e. N.N.W., E.S.E., etc. If the two coincided in regard to direction, the attack commenced. If, however, they did not agree in this important respect, the line of patrol ships advanced another mile and listened again.
The flag-ship of the unit on receiving the direction from one or more ships marked the lines of sound on a chart (as in Fig. 22), and when this was substantiated by another ship the point where the two lines crossed was known to be the position of the hostile submarine, and the attack was ordered.
As to the exact method of an anti-submarine attack little need be said here beyond the fact that the ships advanced at full speed, manoeuvring into a special formation which enabled them to cover about half a square mile of sea with the explosive force of their collective depth charges.
When the attack had been completed all vessels engaged resumed their stations and waited with quick-firing guns ready in case the monster should rise from the deep to make a dying effort to destroy her pursuers.
The tactical methods of anti-submarine attack were, of course, numerous, and they varied according to the speed of the surface ships engaged. What was possible of accomplishment by fast-moving coastal motor boats or the larger-sized M.L.'s proved impracticable for the more heavily armed but slow-moving trawlers and drifters. The tactics of these latter craft were often of the simplest character, and consisted principally of either independent attacks with the aid of hydrophones and depth charges, or, more frequently, the assumption of an innocent air in order to induce the submarine to open the attack at close range.
In many respects this proved the most effective method of anti-submarine warfare. Not only did it frequently cause the under-water craft to rise to the surface and commence the attack by gun-fire, in order not to expend a valuable torpedo on what appeared to be an unarmed and helpless ship, but it also produced a moral effect throughout the German submarine flotillas.
When a few U-boats had been either sunk or damaged in this way the news that every Allied ship was heavily armed circulated among the enemy personnel, and they became very nervous of attacking in any position except totally submerged. This meant the loss of at least one torpedo, out of from five to ten carried, for every attack made, whether successful or unsuccessful, and the latter were predominant.
It soon became apparent that either they must risk surface attacks and so save their torpedoes, or else curtail their cruises to meet the rapid expenditure of their only submarine weapon. This does not, of course, cover the activities of under-water mine-layers, whose nefarious purpose consisted simply of laying their mines wherever they appeared most likely to catch Allied shipping. These craft were usually armed with torpedoes as well as mines, to enable them to continue the work of destruction when the cargo of the latter had been safely laid. In this way the problem of combating the German submarine offensive resolved itself into two parts, one being to checkmate the commerce raider and the other the mine-layer. With the second of these difficulties we shall deal in a later chapter.
Many merchantmen, both Allied and neutral, owed their escape to this camouflage warfare, which was brought to a high pitch of perfection and daring in the now famous mystery ships.
What may be said to form the second method of anti-submarine warfare was the decoy or camouflage system. Of primary importance in this category were the mystery ships already described, but there were also innumerable other ruses de guerre which increased its efficiency.
To describe one of these will enable the reader to draw on his own imagination for the remainder. A vessel was steaming in from the Atlantic and was about a hundred miles from the Cornish coast when she was attacked by a submarine above water. The surface ship was heavily armed, but instead of using her weapons at once she sent out frantic wireless signals for assistance. Every few minutes the call went far and wide in plain Morse.
The shells from the submarine splashed into the sea around, but none struck the target for some minutes. Had the surface ship desired, she could in all probability have avoided the under-water craft by using her superior speed, but instead she dropped back, allowing the submarine to catch up to her, and the shells began to burst unpleasantly close.
Still the frantic wireless calls went forth. First the simple message: "I am being attacked by a large German submarine." Then the vehemence increased to: "I am being heavily shelled." A few minutes elapsed and then the call: "Help. Submarine gaining on me." And finally: "Abandoning ship."
At this point the submarine was close astern and the liner slowing down preparatory to lowering her life-boats. The shells were damaging her superstructure, but a heavy swell interfered with the German marksmanship. Then came the surprise. A life-boat on the liner's poop was hoisted clear of the deck and from under its cover there appeared the lean grey muzzle of a 4.7-inch gun. A few sharp blasts of cordite and the submarine sagged and disappeared.
The captain of the liner had noticed when first attacked that the submarine was fitted with wireless and the calls sent out by him were in plain Morse code. On the strength of these the German commander had saved his torpedoes but lost his ship.
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Another form of anti-submarine tactics was the employment of indicator and mined nets around an apparently disabled ship, or in lines across narrow channels known to be used by German submarines on their way to and from their bases. This method has, however, received full mention in other chapters.
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What may be termed the third system of anti-submarine warfare was the use of extensive mine barriers, specially laid to catch submarines attempting to pass through them under water. The surface of the sea was patrolled by shallow-draft vessels and the under-seas guarded by mines. If a submarine was sighted in the vicinity of one of the mine barriers already described she was attacked and forced to submerge herself in order to escape destruction from the guns of the pursuing surface flotilla. From that moment her fate was sealed. By cautious manoeuvring and using to full advantage their great superiority of speed (20-40 knots against 6-10 knots) the surface ships were able to head their quarry into the mine-field. Usually the submarine dived deep in order to throw her pursuers off the track, and all unconscious of the deep-laid mines in thousands she plunged to her doom—a heavy rumble, followed by an upheaval of the surface, and the chase was over.
This method, when carried out on the vast and scientifically sound principle described in a previous chapter, offers the best possible antidote to the submarine. Its employment in the Great European War placed the seal of complete success on the Allied anti-submarine offensive. It should, however, be remembered that comparatively narrow seas and a restricted zone of major operations made possible of accomplishment with some hundreds of thousands of mines (average cost, L400) what would in many cases and in many seas have been quite impracticable with as many millions of these difficult weapons.
* * * * *
The employment of submarines against submarines also forms a method of under-sea warfare which gives considerable scope for both daring and resource. It is of course quite impossible for one of these vessels when totally submerged to fight another in the same blind condition. But with just the small periscopic tube—or eye of the submarine—projecting above the surface, one craft can scout and watch for another to rise to the surface, thinking no enemy is near, in order to replenish her air supply for breathing or for recharging the electric storage batteries which supply the current for submerged propulsion.
When such a position obtains the submarine which comes unknowingly to the surface stands a grave danger of being torpedoed by her opponent. This actually occurred to at least one German U-boat during the Great War.
One or more submarines can also be employed around a slow-moving decoy ship. In this case they would have the advantage of being invisible until the actual moment of attack. The result of such a manoeuvre would be either a gun duel on the surface or the torpedoing of the attacking submarine by one or other vessel of the decoy's submerged escort.
It was a ruse of this kind which achieved success in the North Sea during the early stages of the war. A trawler was employed to tow a submarine by a submerged hawser. This mode of progress was adopted to enable the submarine to economise the strictly limited supply of electricity carried for under-water propulsion.
The trawler then cruised very slowly about, dragging the submarine under the surface behind her. In order to divert any suspicion which might have been aroused by her slow speed she was rigged so as to give the impression that a net was being towed, and the area of operations chosen was well-known fishing-ground.
In this curious way days were spent before the desired consummation was reached. Then a large U-boat came boldly to the surface and opened fire. Instantly the submarine astern of the trawler was released from the tow rope and forged ahead under her own electric engines. The commander of the surface decoy stopped his ship and commenced lowering the small life-boat carried. This was done in order to distract the attention of the Germans from the tiny periscope which was planing through the water to the attack.
A shell struck the trawler, carrying away her funnel, but did no other damage, and a few seconds later the water around the U-boat rose up in a vast upheaval of white. The plan had succeeded, and when the air cleared of the smoke from the trawler's damaged stack there was nothing afloat on the surface of the sea around—except an ever-widening patch of oil and bubbles.
A few minutes later the thin grey line of the British submarine rose above the swell some five hundred yards distant from the scene of her triumph.
Another means by which one subaqueous fleet can attack another is by laying mines in the seas around the enemy base.
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These simple methods formed what may be termed the backbone of the widespread anti-submarine operations during the Great War, but with the experience gained and the brains of almost every nation focussed on the problem of providing an effective counterblast to the under-water warship, there can be little doubt that in the next great naval conflict new and more scientific means of attacking these pests of the sea will have been perfected, though what degree of success they will attain in the stern trial of war the future alone can tell.[7]
FOOTNOTES:
[6] Greenwich mean time.
[7] For a careful study of the effect of the submarine on the old theories of sea power see Submarines and Sea Power, by Charles Domville-Fife (Messrs George Bell & Sons, Ltd., London, and Messrs Lippincotts, New York.).
CHAPTER XI
THE MYSTERIES OF GERMAN MINE-LAYING EXPLAINED
TO those unversed in modern war it may have appeared strange that, although the Allied navies held command of the sea from the opening of the Great War in 1914 to the signature of Peace in 1919, the Germans were nevertheless able to lay several thousand mines every year off the coasts of England, France and even the most distant colonies and dominions. It often occurred that harbour entrances and narrow fair-ways were repeatedly mined, notwithstanding a vigilant day-and-night watch from the bridges, look-outs and decks of many patrol ships cruising or listening in the vicinity.
The explanation is that the mines were laid by large submarines capable of approaching the coast, laying their deadly cargo from specially constructed stern tubes and retreating to comparative safety far out in the broad ocean, without rising more than momentarily to the surface for the purpose of observation.
This, it may be said, did not absolve the ships listening on their hydrophones, who should have been able to detect the approach of a submarine from the sound of her engines. During the first year of war the hydrophone was a very imperfect instrument, and although the sound might be heard it was quite impossible to tell from what direction it was coming. Later on, when the listening appliances had been greatly improved, there still remained two detrimental factors. The noise of breakers beating against rocks, sands or other obstructions destroyed much of the value of these instruments when used close inshore. On dark and rough nights the roar of wind and sea and the lurching of the vessel rendered subaqueous sounds extremely difficult to detect; and in a fair-way or channel used by surface shipping it was frequently impossible, even in fine but dark weather, to tell if the sound coming up from the sea emanated from a surface ship or a submarine.
If, in the latter case, the patrol ship started her own engines and moved forward in the darkness to ascertain from whence the noise came, she gave away her presence to the hostile submarine, also fitted with listening appliances. Whereas if she remained still and waited for the enemy to approach, mines might be laid in the meantime across important fair-ways which it was her duty to guard.
German mine-laying submarines were designated U-C boats, and often these vessels would employ a ruse in order to lay their mines in safety. Sometimes a decoy would draw the patrols away on a fruitless chase while the mines were being launched from the tubes of another U-C boat. In one case a big armed steamer was attacked with torpedoes while mines were being laid across the line of advance by which a flotilla of warships would be likely to come out to her aid from a near-by base.
In these and other ways over 3000 mines were laid off the British coast in one year. There were also several raids by surface mine-layers, which succeeded in eluding the network of patrols in the fogs and snows which prevail in the North Sea during several months out of every twelve. The two most important of these were the cruises of the Wolfe and the Moewe. The former vessel left Germany during the November fogs of 1916, and, by skirting the Norwegian coast, succeeded in passing the British patrol flotillas. She carried 500 mines, and after crossing the North Sea in high latitudes, proceeded down the mid-Atlantic until off the Cape of Good Hope, where the first mine-field was laid. She then crossed the Indian Ocean, laying fields off Bombay and Colombo.
It was in these seas that she succeeded in capturing a British merchantman. Placing a German crew and a cargo of mines aboard, she sent the prize to lay a field off Aden, while she herself proceeded to New Zealand. In these far-distant waters another field was laid, and a few months later the last of her cargo was discharged off Singapore. From this time onward she became a commerce raider.
[Illustration: FIG. 23.—A typical German mine and sinker. A. The mine-casing containing about 300 lb. of high explosive, and the electric firing device which is put in force when the horns B are struck and bent by a passing ship. B. Horns, made of lead and easily bent if touched by a surface ship, but sufficiently rigid to resist blows by sea-water. C. Hydrostatic device, operated by the pressure of the water at a given depth, rendering the mine safe until submerged. D. Slings holding mine to mooring rope F. F. Mooring rope to reel in sinker. G. Reel of mooring wire, which unwinds when the mine floats to the surface. H. Iron supports held together (as in small left-hand diagram) by a band round the mine-casing. The mine goes overboard and sinks like this to the bottom. The band is then released by a special device, and the supports drop away, leaving the mine free to float to the surface (as in small right-hand diagram). I. A heavy iron sinker which acts as an anchor, holding the mine in one position.]
The Moewe left Germany in December, 1916, and crossed the North Sea amid heavy snow squalls. Proceeding into the North Atlantic, she awaited a favourable opportunity to approach the British coast. This came one wild January night with a rising gale and a haze of snow. All her mines, about 400 in number, were laid off the Scottish coast in the teeth of a nor'wester. Then, with the "jolly Roger at the fore," she steamed out on to the wastes of sea lying between the New World and the Old.
[Illustration: FIG. 24.—Diagram illustrating the effect of tide on a moored mine. A vessel is approaching a mine D, moored to the bottom by a sinker H. The distance from the top of the horns of the mine to the surface of the sea is approximately 5 feet at low tide, and as the vessel's draught is 7 feet she would strike the mine. If, however, the same vessel passed over the same mine a few hours later, at high tide, the level of the sea would have risen 5 feet, and the mine would then be 10 feet below the surface; in which case the ship would just pass over in safety. This is known as the "tide difficulty." There is, in addition, the "dip" of the mine due to the strength of the tidal current. E and F show what is meant by the dip of a mine. It is the deflection from the vertical caused by the ebb and flow of the tide. It frequently causes a mine-field to be quite harmless to passing surface craft except during the period of slack water between tides.]
* * * * *
We now come to the mines themselves and the method of laying them both above and below the surface.
A good idea of the shape, size and general characteristics of these weapons will be obtained from the accompanying diagrams. On being discharged into the sea they automatically adjust themselves to float about ten feet below the surface (according to tide) and are anchored to the bottom by means of a wire mooring rope attached to a heavy sinker. To describe here the mechanical details of all the different types of German submarine mines would occupy many pages with uninteresting technical formulae. It is sufficient to say that they carried an explosive charge (200 to 400 lb. of T.N.T.) sufficient to blow to pieces vessels of several hundred tons and to seriously damage the largest warship. They were intended to float a few feet below the surface—being held down by the mooring rope—but, as there was no means of compensating for the rise and fall of the tide, many of them often showed their horns above the surface at low water and were immersed too deep to be of much use against any but the deepest draught ships at high tide. A reference to Fig. 24 will make this difficulty clear.
There was scarcely a ship afloat in the zone of operations which did not, during those years of storm, sight one or more of these hateful weapons with their horns showing above the surface. Motor launches were employed to scout for them during the hour before and the hour after low water. In this way many hundreds were discovered and destroyed almost as soon as they had been laid. One badly laid mine, which shows on the surface when the tide ebbs, will often give away a whole field of these otherwise invisible weapons, and the work of sweeping them up and destroying them is then rendered comparatively easy.
The effect of strong tides on a moored mine is considerable, and will render a field quite harmless for several hours out of every twenty-four. The reason for this is best described with the aid of a diagram. |
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