The battle of the Atlantic, Mid-March to December 1941.In the latter part of April 1941, 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.Legend: black arcs show aircraft coverage. Green lines are the main convoy routes. Blue dots are merchant ships sunk by the Axis. Red dots are U-boats sunk by the Allies.

Mercator projection; geodetic system WGS84
Coordinates : upper margin is 73°30′ N, right margin is 30° E, left and bottom margins are still to be computed due to cropping
This  is a retouched picture, which means that it has been digitally altered from its original version. Modifications: removing the legend, cropping, one English inscription. The original can be viewed here: The battle of the Atlantic 1941 map-fr.svg: . Modifications made by Incnis Mrsi.
Sémhur (vectorization)
Incnis Mrsi (tweaks)