ing completion. The first step necessary was a
considerable increase in the instructional facilities for training
listeners both for the increased number of shore stations and for the
large number of vessels that were fitted for hydrophone work during the
year.

The greater part of this training took place at the establishment at
Hawkcraig, near Rosyth, at which Captain Ryan, R.N., carried out so much
exceedingly valuable work during the war. 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. In addition to this extensive instructional work
the development of the whole system of detecting the presence of
submarines by sound is very largely due to the work originally carried
out at Hawkcraig by Captain Ryan.

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. Experimental work under Captain Ryan
continued at Hawkcraig during 1915, and in 1916 a section of the Board
of Invention and Research went to Hawkcraig to work in conjunction with
him. This station produced the Mark II directional hydrophone of which
large numbers were ordered in 1917 for use in patrol craft. It was a
great improvement on any hydrophone instrument previously in use.
Hawkcraig also produced the directional plates fitted to our submarines,
as well as many other inventions used in detecting the presence of
submarines.

In addition to the work at Hawkcraig an experimental station under the
Board of Invention and Research was established near Harwich in January,
1917. 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.

"OTTERS" AND PARAVANES

_The "Otter" system_ of defence of merchant ships against mines was
devised by Lieutenant Dennis Burney, D.S.O., R.N. (a son of Admiral Sir
Cecil