By July we had succeeded in increasing the strength of the anti-submarine convoy escorting force to thirty-three destroyers (eleven of which belonged to the United States Navy) and ten sloops, with eleven more destroyers for the screening of troop transports through the submarine zone and for the protection of the convoys eastward from the Lizard, the position in which the other screening force left them. We had remaining twelve sloops, which, with trawlers, were engaged in protecting that considerable portion of the trade making for the south of Ireland, which we could not yet bring under convoy. It was intended to absorb these sloops for convoy protection as soon as circumstances permitted. At this stage it was considered that a total of thirty-three more destroyers or sloops was needed to complete the homeward convoy system. The Admiralty was pressed to weaken yet further the Grand Fleet destroyer force in order to extend the convoy system, but did not consider such a course justified in view of the general naval situation. In arranging the organization of the Atlantic convoy system it was necessary to take into consideration certain other important matters. Amongst these were the following: 1. The selection of ports of assembly and frequency of sailing. During the latter half of 1917 the general arrangements were as follows for the homeward trade: Port of Assembly. Frequency of Sailing. Destination. Gibraltar Every 4 days. Alternately to E. & W. c'ts. Sierra Leone Every 8 days. Either coast. Dakar Every 8 days. Either coast. Hampton Roads (U.S.A.) Every 4 days. Alternately to E. & W. c'ts. New York Every 8 days. Alternately to E. & W. c'ts. Halifax, N.S. Every 8 days. West coast. Sydney (Cape Breton) Every 8 days. Alternately to E. & W. c'ts. Each port served a certain area of trade, and vessels engaged in that trade met at the port of assembly for convoy to the United Kingdom or to France. The total number of merchant ships sailing thus in convoy every eight days in September, 1917, was about 150, in convoys comprising from 12 to 30 ships, and the total escorting forces comprised: 50 ocean escort vessels (old battleships, cruisers, armed merchant ships and armed escort ships), 90 sloops and destroyers, 15 vessels of the "P" class (small destroyers), 50 trawlers, in addition to a considerable force for local escort near Gibraltar, consisting of sloops, yachts, torpedo boats, U.S. revenue cruisers, U.S. tugs, etc.