Communications intelligence and the battle for convoy OG 71, 15–23 August 1941

In 1941, the British instituted a comprehensive system of convoys in the Atlantic. One of the first convoys, OG 71, while sailing between Britain and Gibraltar, was shadowed by German aircraft and attacked by U‐boats. In the ensuing August battle, while no U‐boats were sunk, the British lost, out of a convoy consisting of 22 vessels, two escorts and eight merchant ships. The German victory was not complete owing to the inability of the German aircraft and U‐boats to cooperate successfully as well as the failure of the U‐boats to fight the battle effectively and aggressively. The British also made many mistakes during the defence of Convoy OG 71. The surface escorts made many errors of tactics; as for the British aircraft, owing to an inability to cooperate with the surface forces, they became almost totally ineffective. One bright spot for the British during the battle, however, was communications intelligence. The battle saw the first use of high frequency direction finders and on several occasions skillful use was made of information obtained from enemy radio transmissions. In fact important lessons were learned by the British from such use of communications intelligence which would pave the way for a more effective implementation of such information in future convoy battles.