At the same time the operational work of the Staff was grouped under two heads, the first mainly concerned with operations against the enemy's surface vessels, and the second with the protection of trade and operations against the enemy's under-water warfare, whether the means he employed were submarines or mines. The officer, Vice-Admiral Sir Henry Oliver, K.C.B., charged with the supervision of the first-named work was styled Deputy Chief of the Naval Staff (D.C.N.S.), and the officer connected with the second, Rear-Admiral A.L. Duff, C.B., was given the title of Assistant Chief of the Naval Staff (A.C.N.S.). The duties of Director of the Anti-Submarine Division of the Staff, hitherto carried out by Admiral Duff, were at this time taken over by Captain W.W. Fisher, C.B., who was brought down from the Grand Fleet for the purpose. Captain Dreyer, who had been Admiral Duff's original assistant, had in the meantime been appointed Director of Naval Ordnance, and had been succeeded by Captain H. Walwyn, D.S.O. The Mine-Sweeping Division of the Staff was also formed, and the importance of the question of signal communications was recognized by forming a Signal Section of the Staff. The adoption of the title of Chief of the Naval Staff by the First Sea Lord necessarily made the functions of the Staff executive instead of advisory. The Staff organization at this period is shown graphically below. C.N.S. | +-- D.C.N.S. | . | | . +-- Operations Division. | . | | | . | +-- Home | . | +-- Foreign | . +-- Mobilization Division. | . +-- Signal Section. | . +-- Intelligence Division. | . +-- A.C.N.S. | +-- Trade Division. +-- Convoys Section. +-- Anti-Submarine Division. +-- Mine-Sweeping Division. Stress was laid in a Staff memorandum issued by me on the fact that the various divisions were on no account to work in watertight compartments, but were to be in the closest touch with one another. The dotted line connecting the D.C.N.S. and the A.C.N.S. in the graph was defined as indicating that there should be the fullest co-operation between the different portions of the Staff. In the summer of 1917 the growth of the convoy system necessitated further expansion of the Naval Staff, and a Mercantile Movements Division was added. The duties of this division were to organize and regulate the movements of convoys of merchant ships. A staff of officers had been by this time sent abroad to the ports from which convoys were directed to sail, and the Mercantile Movements Division, acting in close touch with the Ministry of Shipping, arranged the assembly and movements of the convoys and their protection. The organization of the portion of the Staff under the A.C.N.S. at this stage is shown below.