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