What was the very first ship sunk in action in WWII?

The very first ship sunk in action in World War II was the British passenger liner SS Athenia. A German U-boat, U-30, torpedoed her west of Scotland on 3 September 1939, the day Britain and France declared war on Germany.

Athenia was carrying more than 1,400 people, including civilians, refugees, and 300 American passengers. She remained afloat for roughly 14 hours before sinking, and 117 people died. The attack became the first major maritime loss of the European war and helped establish the dangerous reality of unrestricted submarine warfare.

Germany initially denied responsibility, fearing that the deaths of American citizens could bring the United States into the conflict. The denial lasted throughout the war; German responsibility was acknowledged only after the 1945 defeat of Nazi Germany. Athenia is sometimes described more precisely as the first British or British Empire ship sunk by Germany in World War II.