In the case of convoys, however, a different system was necessary owing to the difficulty of transmitting information, the great delay that would be caused were this attempted, and the impossibility of control being exercised over all convoys at sea except by the Admiralty. Consequently the actual movements of convoys for the greater part of their passage were directed by the Naval Staff. Owing to ships not showing lights at night, convoys were diverted clear of one another by wireless signal if they were getting into dangerous proximity; they were directed to alter course as necessary to avoid areas in which submarines had been located, and occasionally it became necessary to alter the destination of some ships as they approached home waters. The movements of all convoys were "plotted" from day to day, indeed from hour to hour, on a large-scale chart at the Admiralty, and it was easy to see at a glance the position of all the ships at any given time. As the convoy approached home waters the ships came within the areas of the Commanders-in-Chief, Coast of Ireland, Devonport, and Portsmouth, and the Vice-Admiral Commanding the Dover Patrol, and were taken in charge by one or other of them. At each port a staff existed which kept a constant record of the movements of ships passing through or working in the Command, and enabled the Commander-in-Chief to take instant action if occasion arose. The success of the convoy system in protecting trade is best shown by the figures relating to the year 1917 on the succeeding page (p. 144). In considering these figures the loose station-keeping of the ships in the Scandinavian convoy must be borne in mind. A large proportion of the ships in this convoy were neutrals, and it was naturally not possible to bring these vessels under discipline as was the case with convoys composed of purely British ships. Consequently there was much straggling, and the losses were proportionately heavier than in most of the Atlantic convoys. The comparatively heavy losses in the Gibraltar convoys were probably due to these convoys traversing two dangerous submarine zones. The extraordinary immunity of the French coal trade convoy from serious losses is remarkable and is probably due to the short passage which enabled most of the distance to be traversed at night and to the ships being of light draught. The table on the following page would not be complete were no reference made to the heavy losses which were experienced during the year amongst ships which were _unescorted_ through the danger zones, owing to the fact that no escorting vessels were available for the work. LOSSES IN HOMEWARD BOUND CONVOYS, 1917.