The battle of the Atlantic, mid-march to december 1941.In the latter part of April, sweeps and searches replaced close escort. In May 1941 these extends 350 miles from Iceland and Northern Ireland.
Operations from West African bases began on 24 March 1941.Hudsons and Catalinas operated from Gibraltar up to 250 miles.

Mercator projection; geodetic system WGS84
Coordinates : 73°30′ N, 56°30′ S, 30° E, 100° W
Own work. Source :

Convoy_routes_1941.jpg by Dennis Richards, HMSO, LONDON
Shores : NGDC World Data Bank II (public domain)
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