On 23 September 1940, during the Battle of Dakar she was badly damaged by depth charges from HMS Fortune and was then scuttled.

Propulsion while surfaced was provided by two 6,000 hp (4,500 kW) diesel motors, with a maximum speed of 18.6 knots (34.4 km/h; 21.4 mph).

Designated as "large cruiser submarines" (French: « sous-marins de grande croisière »), their surfaced range was 10,000 nautical miles (19,000 km; 12,000 mi) at 10 knots (19 km/h; 12 mph), and 14,000 nautical miles (26,000 km; 16,000 mi) at 7 knots (13 km/h; 8.1 mph), with a submerged range of 100 nautical miles (190 km; 120 mi) at 5 knots (9.3 km/h; 5.8 mph).

[1] At the start of World War II, Ajax was assigned to the 6th Submarine Division, based in Brest, along with her sister ships Persée, Archimède and Poncelet.

[8] In front of the advancing German forces, she left Brest along 6:30 pm with thirteen other French submarines and one tanker.