The number of vessels composing a convoy varied, but often exceeded twenty big cargo ships, carrying some 120,000 tons of merchandise, or six liners, with 20,000 troops on board, while the escorting flotilla consisted of a light cruiser, acting as flag-ship, six destroyers, two special vessels ("P" boats) towing observation airships, and some eight or ten trawlers, with possibly one or more seaplanes and several M.L.'s for the first few miles of the voyage. The destroyers were spread out ahead and on the flanks of the fleet, and by using their greatly superior speed were able to zigzag and circle round the whole convoy.
Fig. 18.—Diagram showing the disposition of a convoy of troops, munitions or food.
In the event of an attack the whole fleet turned off from the course they were steering at a sharp angle, showing only their sterns to the U-boat. A destroyer acted as rearguard to prevent any of the convoyed ships from straggling. When the fleet had arrived at a rendezvous far out in the open sea, where the danger of a submarine attack was much less, the escort handed over their charges to one or two ocean-going cruisers, which stayed with the merchant ships throughout the remainder of their voyage.
Yachting Monthly
The escorting flotilla then cruised about in the vicinity of the rendezvous until an incoming convoy appeared. These ships were then taken over from their mid-ocean cruiser guard and escorted back through the danger zone to port, and so the game of war continued until months became years.
All this may sound straightforward and quite simple, but there were difficulties, to say nothing of dangers, which made it a most arduous operation. First came the speed problem. Every merchant ship differed in this important respect, so the speed of the slowest unit became the speed of the entire fleet, and this reduction made an attack by under-water craft much easier of accomplishment. Hence the call for "standard ships," which is a point that should be borne in mind by future generations as a safeguard against blockade. Then came the question of destination, which increased the number of escorting flotillas, and especially ocean cruiser guards, required for a given number of cargo ships. Next there was the loading and unloading to be considered, involving long hours and hard work by the men on the quaysides. This great difficulty was one of the reasons for the formation of docker battalions. Coaling such big fleets by given times caused many grey hairs to appear where otherwise they would not have been. Finally there was the danger of mines having been laid in the fair-ways leading to the port, which necessitated every convoy being met by special vessels to sweep the seas in front of each incoming and outgoing fleet.
Fig. 19.—Diagram showing the convoy system.