Surcouf was the French submarine that carried a twin 203 mm gun turret and served during World War II. Commissioned in 1934, she was named after the French privateer Robert Surcouf and was built as a large “underwater cruiser.”
Her unusual armament included two 203 mm guns in a forward turret, a calibre comparable to the main guns of some cruisers. She also carried torpedoes, a reconnaissance aircraft in a hangar, and space for a large crew. The concept was to let the submarine attack merchant ships and surface warships with gunfire while using submerged operations for concealment.
Surcouf joined the Free French Naval Forces after France’s defeat in 1940. She disappeared in the Caribbean in February 1942 after colliding with the American freighter Thompson Lykes. All crew members and passengers aboard were lost.
Surcouf is often described as the largest submarine in the world when launched, but that distinction later passed to larger Japanese submarine designs such as the I-400 class.