use of fast coastal
motor-boats for anti-submarine work, the production of mines of an
improved type for use especially against submarines, very considerable
developments in the use of minefields, especially deep minefields,
including persistent mining in the Heligoland Bight and the laying of a
complete minefield at varying depths in the Straits of Dover; also,
after the United States entered the war, the laying of a very extensive
minefield right across the northern part of the North Sea. The provision
of "flares" for illuminating minefields at night, and a system of
submarine detection by the use of electrical apparatus were also matters
which were taken up and pressed forward during 1917. During the year the
system of dazzle painting for merchant ships was brought into general
use.

On the operational side of the Naval Staff the work of dealing with
enemy submarines before they passed out of the North Sea was taken in
hand by organized hunting operations by destroyers and other patrol
craft, and by the more extended use offensively of our own submarines,
as vessels became available.

Considerable developments were effected in the matter of the control of
mercantile traffic, and much was done to train the personnel of the
mercantile marine in matters relating to submarine warfare.

Taking these subjects in detail, it will be of interest to examine the
progress made during the year.

HOWITZERS

The _howitzer_ as a weapon for use against the submarine when submerged
was almost non-existent at the beginning of 1917, only thirty
bomb-throwers, on the lines of trench-mortars, being on order. By April
of that year designs for seven different kinds of bomb-throwers and
howitzers had been prepared and approved, and orders placed for 1,006
weapons, of which number the first 41 were due for delivery in May. By
the end of May the number of bomb-throwers and howitzers on order had
been increased to 2,056, of eight different patterns. Over 1,000 of
these weapons fired a bomb or shell carrying a burster exceeding 90 lbs.
in weight, and with a range varying between 1,200 and 2,600 yards. Later
in the war, as we gained experience of the value of this form of attack,
heavier bombs were introduced for use in the existing bomb-throwers and
howitzers. The howitzer as an anti-submarine weapon was handicapped by
the comparatively small weight of the bursting charge of its shell. This
applied more particularly to the earlier patte