SURCOUF was the largest submarine ever built, at the time, displacing 3,250 tonnes surfaced. She mounted a twin 8 inch gun turret with a maximum range of 26,000m, anti aircraft guns, ten torpedo tubes, a floatplane and a motorboat, and had a cargo compartment capable of holding 40 passengers or prisoners.
When the Germans invaded France in 1940, she was being refitted in Brest but, unable to dive, made a surfaced transit and sought sanctuary in Plymouth. On 3 July 1940, the submarine was boarded by armed marines, sailors and soldiers, to be taken under British control. There was some resistance during which Commander Sprague, leading the party, and Lieutenant Griffiths were fatally wounded.
SURCOUF refit was completed and the submarine was turned over to the Free French Navy, after which she was employed on convoy protection. In January 1942 it was decided to send SURCOUF to the Pacific theatre and she set off for Australia via the Panama Canal. She disappeared on the night of 18/19 February 1942 about 70 nm North of Cristobal.
Although many theories were advanced as to the cause of her loss, the most likely is that she was run down by the American freighter Thompson Lykes. The freighter reported hitting a partially submerged object and hearing cries for help, in English, but did not stop, thinking she had hit a U-Boat. The submarine was lost with its entire crew of about 120, including a three man Royal Navy liaison team.