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.

Motor Launches were organized into submarine hunting flotillas during the year 1917.  These vessels were equipped with the directional hydrophone as soon as its utility was established, and were supplied with depth charges.  In the summer of 1917 four such hunting flotillas were busy in the Channel; the work of one of these I have described already, and they certainly contributed towards making the Channel an uneasy place for submarine operations.

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: 

Supply of        Directional
Date        General Service  Mark I and      Shark Fin    Fish
1917.        Portable Type.    Mark II.         Type.         Type.

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