French submarine ordered to be built in December 1927, launched 18 October 1929, and commissioned in May 1934. Surcouf, named after the French privateer Robert Surcouf, was the largest submarine ever built, until being surpassed by the Japanese I-400. Her short wartime career was marked with controversy and conspiracy theories. She was classified as an "undersea cruiser" by sources of her time. Surcouf was designed as an "underwater cruiser ", intended to seek and engage in surface combat.For reconnaissance, she carried a Besson MB.411 observation float plane in a hangar built abaft of the conning tower; for combat, she was armed with eight x 550mm and four x 400 mm torpedo tubes and twin 203mm 50 Modèle 1924 guns in a pressure-tight turret forward of the conning tower.By August 1940, the British completed Surcouf's refit and turned her over to the Free French Navy (Forces Navales Françaises Libres, FNFL) for convoy patrol. The Surcouf was sunk on 18 February 1942. The Surcouf was rammed at night in the Caribbean by the American freighter SS Thompson Lykes.