Redoutable class submarine (1931)

The Redoubtable-class Ajax, circa 1930
Class overview
Name:	Redoutable class
Operators:	French Navy  Free French Naval Forces  Vichy French Navy
Subclasses:	Type I - Le Redoutable Type II - Le Pascal
Completed:	31
Lost:	26
Retired:	5
General characteristics
Type:	Submarine
Displacement:	1,500 tonnes (1,476 long tons) (surfaced) 2,000 tonnes (1,968 long tons) (submerged)
Length:	92.3 m (302 ft 10 in)
Beam:	8.2 m (26 ft 11 in)
Draught:	4.9 m (16 ft 1 in)
Propulsion:	2 × diesel engines, 4,300 hp (3,207 kW) 2 × electric motors, 1,200 hp (895 kW)
Speed:	17 knots (31 km/h; 20 mph) (surfaced) 10 knots (19 km/h; 12 mph) (submerged)
Range:	14,000 nautical miles (26,000 km) at 7 knots (13 km/h) 10,000 nautical miles (20,000 km) at 10 knots (20 km/h) 4,000 nautical miles (7,000 km) at 17 knots (31 km/h) 90 nautical miles (170 km) at 7 knots (13 km/h) (submerged)
Test depth:	80 m (260 ft)
Complement:	5 officers (6 in operations) 79 men
Armament:	9 × 550 mm (21.7 in) torpedo tubes 2 × 400 mm (15.7 in) torpedo tubes 1 × 100 mm (4 in) deck gun 2 × 13.2 mm (0.52 in) machine guns

The Redoutable-class submarines were 31 submarines with air-independent propulsion built in France between 1924 and 1937 for the French Navy. Most of the class saw service during the Second World War. The class is also known in French as the Classe 1 500 tonnes, and they were designated as "First Class submarines", or "large submarine cruisers". They are known as the Redoutable class in reference to the lead boat Redoutable (), in service from 1931 to 1942. The class is divided into two sub-class series, Type I, known as Le Redoutable and Type II, Pascal.

Modern submarines when they were designed, they quickly became outdated, and were approaching obsolescence by the beginning of the Second World War. The conditions of the Armistice of 22 June 1940 prevented the Vichy government from carrying out a modernization programme. 24 out of the 29 units that served in the war were lost. Used in the defence of the Second French colonial empire under the Vichy regime, submarines of the class saw action against Allied offensives at the Battles of Dakar, Libreville and Madagascar. Many of the submarines of the class came under Allied control after the Allied landings in North Africa. Few however saw much further active service after this due to a period of refitting and alterations done in the United States between February 1943 and March 1945. Once exception was Casabianca, which took part in the liberation of Corsica. The surviving submarines were largely used for training purposes after the war, with the last of them being disarmed in 1952.