The Crisis of the Naval War

by John Rushworth Jellicoe

It is as well to correct a common misapprehension as to the value of depth charges in destroying submarines.

Many people held very exaggerated ideas on this subject, even to the extent of supposing that a depth charge would destroy a submarine if dropped within several hundred yards of her. This is, unfortunately, very far indeed from being the case; it is, on the contrary, necessary to explode the charge near the submarine in order to effect destruction. Taking the depth charge with 300 lb. weight of explosive, ordinarily supplied to destroyers in 1917, it was necessary to explode it within fourteen feet of a submarine to ensure destruction; at distances up to about twenty-eight feet from the hull the depth charge might be expected to disable a submarine to the extent of forcing her to the surface, when she could be sunk by gun-fire or rammed, and at distances up to sixty feet the moral effect on the crew would be considerable and might force the submarine to the surface.

A consideration of these figures will show that it was necessary for a vessel attacking a submarine with depth charges to drop them in very close proximity, and the first obvious difficulty was to ascertain the position of a submarine that had dived and was out of sight.

Unless, therefore, the attacking vessel was fairly close to the submarine at the moment of the latter diving there was but little chance of the attack being successful.

HYDROPHONES

The Hydrophone, for use in locating submerged submarines, although first evolved in 1915, was in its infancy, so far as supply to ships was concerned, at the commencement of 1917. Experiments were being carried out by the Board of Invention and Research at Harwich, and by Captain Ryan, R.N., at Hawkcraig, and although very useful results had been obtained and a considerable number of shore stations as well as some patrol vessels had been fitted with hydrophones, which had a listening range of one or two miles, all the devices for use afloat suffered from the disadvantage that it was not possible to use them whilst the ship carrying them was moving, since the noise of the vessel's own machinery and of the water passing along the side prevented the noise made by other vessels being located. What was required was a listening instrument that could be used by a ship moving at least at slow speed, otherwise the ship carrying the hydrophone was herself, when stopped, an easy target for the submarine's torpedo. It was also essential, before an attack could be delivered, to be able to locate the direction of the enemy submarine, and prior to 1917 all that these instruments showed was the presence of a submarine somewhere in the vicinity.

Much research and experimental work was carried out during the year 1917 under the encouragement and supervision of the Anti-Submarine Division of the Naval Staff. Two hydrophones were invented in the early part of 1917, one by Captain Ryan, R.N., and one by the Board of Invention and Research, which could be used from ships at very slow speed and which gave some indication of the direction of the sound; finally, in the summer of 1917, the ability and patience of one inventor, Mr. Nash, were rewarded, and an instrument was devised termed the "fish" hydrophone which to a considerable extent fulfilled the required conditions. Mr. Nash, whose invention had been considered but not adopted by the Board of Invention and Research before he brought it to the Anti-Submarine Division of the Naval Staff, laboured under many difficulties with the greatest energy and perseverance; various modifications in the design were effected until, in October, 1917, the instrument was pronounced satisfactory and supplies were put in hand.

The next step was to fit the "fish" hydrophone in certain auxiliary patrol vessels as well as some destroyers, "P" boats and motor launches, to enter and train men to work it, and finally to organize these vessels into "submarine hunting flotillas," drill them, and then set them to their task.

This work, which occupied some time, was carried out at Portland, where a regular establishment was set up for developing the "fish" hydrophone and for organizing and training the "hunting flotillas" in its use. A considerable amount of training in the use of the hydrophone was required before men became efficient, and only those with a very keen sense of hearing were suited to the work. The chances of the success of the hunting flotillas had been promising in the early experiments, and the fitting out of patrol craft and organizing and drilling them, proceeded as rapidly as the vessels could be obtained, but largely owing to the slow production of trawlers it was not until November that the first hunting flotilla fitted with the "fish" hydrophone was actually at work. The progress made after this date is illustrated by the fact that in December, 1917, a division of drifters, with a "P" boat, fitted with this "fish" hydrophone hunted an enemy submarine for seven hours during darkness, covering a distance of fifty miles, kept touch with her by sound throughout this period, and finished by dropping depth charges in apparently the correct position, since a strong smell of oil fuel resulted and nothing further could be heard of the submarine, although the drifters listened for several hours. On another occasion in the same month a division of drifters hunted a submarine for five hours. The number of hydrophones was increased as rapidly as possible until by the end of the year the system was in full operation within a limited area, and only required expansion to work, as was intended, on a large scale in the North Sea and the English Channel.

Meanwhile during 1917 directional hydrophones, which had been successfully produced both by Captain Ryan and by the Board of Invention and Research, had been fitted to patrol craft in large numbers, and "hunting flotillas" were operating in many areas. A good example of the working of one of these flotillas occurred off Dartmouth in the summer of 1918, when a division of motor launches fitted with the Mark II hydrophone, under the general guidance of a destroyer, carried out a successful attack on a German submarine. Early in the afternoon one of the motor launches dropped a depth charge on an oil patch, and shortly afterwards one of the hydrophones picked up the sound of an internal combustion engine; a line of depth charges was run on the bearing indicated by the hydrophone. The motor launches and the destroyer remained listening, until at about 6.0 P.M. a submarine came to the surface not far from Motor Launch No. 135, which fired two rounds at the submarine before the latter submerged. Other motor launches closed in, and depth charges were dropped by them in close proximity to the wash of the submarine. Oil came to the surface, and more depth charges were dropped in large numbers on the spot for the ensuing forty-eight hours. Eventually objects came to the surface clearly indicating the presence of a submarine. Further charges were dropped, and an obstruction on the bottom was located by means of a sweep. This engagement held peculiar interest for me, since during my visit to Canada in the winter of 1919 the honour fell to me of presenting to a Canadian—Lieutenant G.L. Cassady, R.N.V.R.—at Vancouver the Distinguished Service Cross awarded him by His Majesty for his work in Motor Launch No. 135 on this occasion.