The S. S. Athenia was the first British ship to be sunk by Germany in World War II. On September 3, 1939, just hours after the British Empire declared war on Germany, U-boat 33 sunk the Athenia passanger ship, mistaking it for an armoured cruiser. The 13,500 ton passenger liner was carrying 1,103 civilians, including more than 300 Americans, which led to German fears that the incident would bring the US into the war.
External Links
Uboat.net Article