Submarine Warfare of To-Day

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 man?uvre 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.

^{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 (? 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.

^{Fig. 12.—Diagram showing a submarine entangled in a submerged net. The submarine A after passing 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 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