A very large proportion of the successful anti-submarine devices brought into use during 1917, and continued throughout the year 1918, were the outcome of the work of the Anti-Submarine Division of the Naval Staff, and it is but just that the high value of this work should be recognized when the history of the war comes to be written by future historians. As has been stated in Chapter I, Rear-Admiral A.C. Duff, C.B., was the original head of the division, with Captain F.C. Dreyer, C.B., Commander Yeats Brown, and Commander Reginald Henderson as his immediate assistants. Captain H.T. Walwyn took the place of Captain Dreyer on March 1, 1917, when the latter officer became Director of Naval Ordnance. When Admiral Duff was appointed Assistant Chief of the Naval Staff, with a seat on the Board, in May, 1917, Captain W.W. Fisher, C.B., became head of the division, which still remained one of the divisions of the Staff working immediately under the A.C.N.S. It is to these officers, with their most zealous, clever and efficient staff, that the institution of many of the successful anti-submarine measures is largely due. They were indefatigable in their search for new methods and in working out and perfecting fresh schemes, and they kept their minds open to _new ideas_. They received much valuable assistance from the great civilian scientists who gave such ready help during the war, the function of the naval officers working with the scientists being to see that the effort was being directed along practical lines. They were also greatly indebted to Captain Ryan, R.N., for the exceedingly valuable work carried out by him at the experimental establishment at Hawkcraig. Many brilliant ideas were due to Captain Ryan's clever brain. I doubt whether the debt due to Admiral Duff and Captain Fisher and their staff for their great work can ever be thoroughly appreciated, but it is certainly my duty to mention it here since I am better able to speak of it than any other person. In saying this I do not wish to detract in the least from the value of the part performed by those to whose lot it fell to put the actual schemes into operation. Without them, of course, nothing could have been accomplished. When the Anti-Submarine Division started in December, 1916, the earlier devices to which attention was devoted were: (1) The design and manufacture of howitzers firing shell fitted to explode some 40 to 60 feet under water with which to attack submarines when submerged. (2) The introduction of a more suitable projectile for use against submarines than that supplied at the time to the guns of destroyers and patrol craft. (3) The improvement of and great increase in the supply of smoke apparatus for the screening of merchant ships from submarines attacking by gunfire. (4) A great increase in the number of depth charges supplied to destroyers and other small craft.