Fact Sheet 3
Convoys
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| Convoy of merchant ships getting ready to sail to Britain. |
The convoy system, which was successfully used in the First World War, was re-introduced at the beginning of the Second World War as the best way to protect the Atlantic seaways from U-boat or surface raiders.
Convoys of up to 100 ships in columns one thousand yards apart and 400 yards separation in line ahead, covered a huge area, typically protected by an escort to merchantman ratio of 1 to 10.
Convoys were divided into slow convoys for ships that could not maintain a steady speed of 10 knots, and fast convoys for ships capable of speeds between 10 and 15 knots. Convoys travelled at the speed of their slowest ship. The Admiralty allowed ships capable of speeds over 15 knots to travel on their own as independents. German U-Boats averaged 17.5 knots on the surface, 7 knots submerged. The Modified Black Swan-class sloops (which included HMS Whimbrel) were capable of speeds of 20-25 knots, allowing them to outrun the U-Boats.
The success of the convoy system was greatly dependent upon the number of escort vessels available. Their chronic shortage in the early years of the war was the most serious problem. The introduction of the BLACK SWANS and later RN RIVER and USN CAPTAIN class frigates from 1943 onwards bolstered the flagging efforts of the corvettes (easily built patrol and escort vessles) and together with long range maritime aircraft became the backbone of an effective combined escort force.
