German submarine U-81 was a Type VIIC U-boat of the navy (Kriegsmarine) of Nazi Germany during World War II, famous for sinking the aircraft carrier HMS Ark Royal.

Convoy SC 42 was the 42nd of the numbered series of World War II Slow Convoys of merchant ships from Sydney, Cape Breton Island to Liverpool. SC 42 was attacked over a three night period in September 1941, losing 16 ships sunk and 4 damaged. This was the worst Allied loss following the attack on convoy SC 7 the previous year. Two attacking U-boats were destroyed.