In another form the apparatus was thrown overboard and formed a smoke cloud on the water.

The rate of supply of sets of the smoke apparatus to ships is shown by the following figures: 

April 1, 1917 — 1,372 sets
July 3, 1917 — 2,563 sets
October 5, 1917 — 3,445 sets
November 26, 1917 — 3,976 sets

DEPTH CHARGES

Depth charges, as supplied to ships in 1917, were of two patterns:  one, Type D, contained a charge of 300 lb. of T.N.T., and the other, Type D*, carried 120 lb. of T.N.T.  At the commencement of 1917 the allowance to ships was two of Type D and two of Type D*, and the supply was insufficient at that time to keep up the stock required to maintain on board four per destroyer, the number for which they were fitted, or to supply all trawlers and other patrol craft with their allowance.  The great value of the depth charge as a weapon against submarines, and the large number that were required for successful attack, became apparent early in 1917, and the allowance was increased.  Difficulty was experienced throughout the year in maintaining adequate stocks owing to the shortage of labour and the many demands on our industries made by the war, but the improvement is shown by the fact that while the average output per week of depth charges was only 140 in July, it had become over 500 by October, and that by the end of December it was raised to over 800, and was still increasing very rapidly.  As a consequence, early in 1918 it was found possible to increase the supply very largely, as many as 30 to 40 per destroyer being carried.

Improvements in the details of depth charges were effected during 1917.  One such improvement was the introduction of a pistol capable of firing at much greater depths than had been in use before.  The result was that all vessels, whether fast or slow, could safely use the 300-lb. depth charge if set to a sufficient depth.  This led to the abolition of the Type D* charges and the universal supply of Type D.

In spite of the difficulties of dropping depth charges so close to submarines as to damage them sufficiently to cause them to come to the surface, very good results were obtained from their use when destroyers carried enough to form, so to speak, a ring round the assumed position at which the submarine had dived.  In order to encourage scientific attack on submarines, a system of depth charge “Battle Practice” was introduced towards the end of 1917.

It is as well to correct a common misapprehension as to the value of depth charges in destroying submarines.