Submarine Warfare of To-day Part 6

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.

[Ill.u.s.tration: FIG. 10.--Diagram ill.u.s.trating a depth charge attack on a submerged submarine. _A._ Motor launch, which has dropped a depth charge to destroy a submarine _B_ travelling at a depth of 90 feet below the surface. _C_ is the depth charge sinking as the M.L. steams away from the danger area. _D_ is the point (80 feet below the surface) at which it will explode, and _E_ indicates the danger area for the submarine _B_.]

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 pa.s.sing 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.

[Ill.u.s.tration: FIG. 11.--Diagram showing princ.i.p.al 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 gla.s.s b.a.l.l.s, 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 pa.s.sing 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 gla.s.s 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 pa.s.sed 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.

[Ill.u.s.tration: FIG. 12.--Diagram showing a submarine entangled in a submerged net. The submarine _A_ after pa.s.sing through a line of nets emerges with her bows enveloped by one section _B_ which she has carried out of its wire-rope frame. The flaming buoy _C_, betraying her movements, is being towed along the surface.]

A considerable measure of success attended the use of this ingenious device until "Fritz" became shy of waters close insh.o.r.e, and kept a careful look-out for possible lines of indicator nets when forced to pa.s.s 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 pa.s.sed 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.

[Ill.u.s.tration: FIG. 13.--Diagram showing a vessel towing a modified sweep. This appliance consists of an armoured electric cable _G_ towed in vertical loop under the surface. The floats _D_ support the 100-lb.

charges _E_, which have strikers attached. If a submarine _B_ is lying "doggo" on the sea-bed one or other of these charges may strike her hull and the whole line then blows up, shattering everything in the surrounding sea. If the strikers fitted on the charges do not touch the submarine the whole line can be exploded at will from the surface ship by closing an electric circuit.]

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.

[Ill.u.s.tration: FIG. 14.--A lance bomb. The wooden handle _A_ enables the charge _B_ (7 lb. of high explosive) to be whirled round the head and hurled a distance of about twenty yards.]

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 pa.s.sing 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, pa.s.s 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.

[Ill.u.s.tration: FIG. 15.--A camouflaged ship. It will be observed that a vessel so painted would, from a distance of several miles, give the appearance of a ship sinking while headed in the opposite direction.]

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 pa.s.senger 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