Other devices followed, many of which were the outcome of work in other Admiralty Departments, particularly the Departments of the Director of Naval Ordnance and the Director of Torpedoes and Mines, working in conjunction with the Anti-Submarine or the Operations Division of the Naval Staff.  Some of the new features were the development of depth-charge throwers, the manufacture and 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 patterns, and to inflict fatal injury it was necessary to burst the shell in close proximity to the submerged submarine.  This weapon, although not very popular at first, soon, however, proved its value, when employed both from patrol craft and from merchant ships.