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.

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.

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.

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 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.

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.

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.

These vessels were equipped with the directional hydrophone as soon as its utility was established, and were supplied with depth charges.

These results were, of course, greatly improved on in 1918, as the numbers of ships fitted with the "fish" and other hydrophones increased and further experience was gained.

The progress in supply of hydrophones is shown by the following table:

Jul 31 2,750 500 - - Aug 31 2,750 700 - - Sep 30 2,750 850 - - Oct 31 3,500 1,000 - - Dec 31 3,680 1,950 870 37 HYDROPHONE STATIONS AND TRAINING SCHOOLS

At the beginning of 1917 four shore hydrophone stations were in use.

I am not able to give exact figures of the number of officers and men who were instructed in hydrophone work either at Hawkcraig or at other stations by instructors sent from Hawkcraig, but the total was certainly upwards of 1,000 officers and 2,000 men.

The first hydrophone station which was established in the spring of 1915 was from Oxcars Lighthouse in the Firth of Forth; it was later in the year transferred to Inchcolm.

It was a great improvement on any hydrophone instrument previously in use.

The Mark I directional hydrophone was designed at this establishment in 1917, and other exceedingly valuable work was carried out there connected with the detection of submarines.

At Malta an experimental station, with a hydrophone training school, was started in the autumn of 1917, and good work was done both there and at a hydrophone station established to the southward of Otranto at about the same time, as well as at a hydrophone training school started at Gallipoli at the end of the year.

At Malta an experimental station, with a hydrophone training school, was started in the autumn of 1917, and good work was done both there and at a hydrophone station established to the southward of Otranto at about the same time, as well as at a hydrophone training school started at Gallipoli at the end of the year.

The surface measures were described as follows: In twelve of the twenty-two areas into which the waters round the United Kingdom were divided, regular hunting flotillas were at work, comprising trawlers and motor launches fitted with hydrophones.

Some were also fitted with hydrophones and formed hunting flotillas, and some were engaged in minesweeping duties, or in patrolling swept channels.

The motor launches were employed for anti-submarine work, fitted with hydrophones, and worked in company with drifters and torpedo-boat destroyers, or in minesweeping in areas in which their light draught rendered it advantageous and safer to employ them instead of heavier draught vessels to locate minefields, and in the Dover area they were largely used to work smoke screens for operations on the Belgian coast.