U-boat: the secret menace (Purnells history of the Second World

The struggle for the sealanes mounted to a climax in March 1943 when the U-Boats pounced on two transatlantic convoys bound for Britain. As the fast convoy HX229 of 40 ships caught up with the slow convoy SC122 of 54 ships, the two groups merged into one and their willing but wholly inadequate escorts were stretched beyond the limit.