Propelled on the surface by two diesel engines producing a combined 6,000 horsepower (4,474 kW), they had a maximum speed of 18.6 knots (34.4 km/h; 21.4 mph).

[3] She was based in French Indochina from May to October 1938 with her sister ship Le Tonnant, then returned to Toulon, where both submarines arrived on 15 December 1938.

When the attack on Mers-el-Kébir — in which a British Royal Navy squadron attacked a French Navy squadron moored at the naval base at Mers El Kébir in Oran on the coast of Algeria — took place on 3 July 1940, she was a part of Group A at Toulon along with her sister ships Archimède and L'Espoir.

[3] The three submarines received orders that day to form a patrol line in the Mediterranean Sea to attack British ships and protect Oran, the line to be formed on the night of 6–7 July 1940 and to extend from north to south for a distance of 20 nautical miles (37 km; 23 mi) east of Alboran Island.

[3] Although Le Conquérant's attack periscope was not installed and she had no torpedoes aboard,[8] leaving her unfit for combat, she was launched from drydock and cast off at 08:00.

[3] Ordered to make for either Dakar in Senegal or Port-Étienne in Mauritania, Le Conquérant got underway from Casablanca on 9 November 1942 at either 05:00 or in the evening, according to different sources.

Le Conquérant was on the surface bound for Dakar off Cisneros in Río de Oro on 13 November 1942 when two PBY Catalina flying boats of U.S. Navy Patrol Squadron 92 (VP-92) sighted her.

They then attacked her with depth charges, blowing her conning tower off and sinking her immediately about 700 nautical miles (1,300 km; 810 mi) southwest of Casablanca with the loss of her entire crew of 57.

[3] As a result of a postwar examination of records to determine the identity of the PBYs' victim, the U.S. Navy proposed in 1948 that they had sunk Le Conquérant′s sister ship Sidi Ferruch.