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. Fig. 11.—Diagram showing principal features of a line of submerged indicator nets. 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 (½ 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 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 Fig. 12.—Diagram showing a submarine entangled in a submerged net. 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 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, Fig. 13.—Diagram showing a vessel towing a modified sweep. 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 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. Fig. 14.—A lance bomb. 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 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. 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, Fig. 15.—A camouflaged ship. 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 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. |