Although these were modern submarines when they were designed, they quickly became outdated and were approaching obsolescence by the beginning of the Second World War.

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.

France sought to expand its submarine forces – which were not limited by the treaty – as an essential tool to defend its coastline and empire.

Roquebert was tasked with creating a "grand cruiser" type of submarine, with the role of carrying out surveillance of an adversary's bases, destroying their communications by attacking their ships, while protecting French colonies.

[4] Construction of the Type I project submarines, starting with Redoutable, was approved by the superior council of the navy on 1 July 1924.

The large construction program made it necessary to contract work out to private shipyards, such as those at Caen or on the Loire, as well as the various naval bases.

They were assigned to operate with their respective squadrons, attack or capture enemy ships, and protect the Franco-British lines of communication.

[24] During the winter of 1939–1940, Achille, Casabianca, Pasteur, and Sfax escorted three Allied convoys from Halifax, Nova Scotia to the United Kingdom.

Fresnel, Le Tonnant, Redoutable, and Vengeur patrolled along the Tunisian coast to prevent an Italian landing, while Centaure and Pascal conducted surveillance operations south of Sardinia.

[27] With the German advance in June, the port of Cherbourg and the arsenal of Brest were evacuated, ships principally heading towards Casablanca and Dakar.

[29] The cause of this lack of success was the utilization of the submarines as escorteurs and squadron eclaireurs, instead of as chasseurs, in strict adherence to the terms of the Treaty of London, coupled with problems associated with the age and obsolescence of the vessels.

[30][31] The conditions of the armistice envisaged the return of French naval vessels to their home ports to be disarmed; however, the British attack on Mers-el-Kébir on 3 July convinced the Germans to cancel this plan.

On 25 September Bévéziers, under the command of Capitaine de corvette Lancelot, attacked and damaged the battleship HMS Resolution, which was out of service for almost nine months.

[33] On 28 October the French naval forces were re-constituted under Vichy government control, under the direction of the German and Italian armistice commissions.

[34] Those submarines on active service were relieved one after the other in pairs by units from Toulon, in order to conduct necessary repairs and refits.

Sfax was accidentally sunk by the German submarine U-37 with the replenishment ship Rhône on 19 December, while they were en route to Dakar to reinforce the fleet based there.

Two days later, Le Héros sank the cargo vessel Thode Fagelund off East London, Eastern Cape.

Monge, after having launched one torpedo at the Illustrious-class aircraft carrier HMS Indomitable, was spotted, fired upon by three destroyers and sunk.

Le Tonnant was ordered to head to Toulon, but realising that this was impossible, her captain had the crew disembark off Cádiz, and then scuttled the submarine.

[44] On 9 November a number of the French submarines at Toulon, Casabianca, Redoutable, Glorieux, Pascal and Henri Poincaré received authorization from the German and Italian armistice commissions to undergo rearming.

French Navy personnel had to decide between their oath of fidelity to Marshal Philippe Pétain, and their desire to join the Allies in Algeria.

Nine Redoutable-class submarines were at Toulon: Fresnel, Achéron, Vengeur, and L'Espoir were in dry docks and the Casabianca, Le Glorieux, Redoutable, Henri Poincare, and Pascal were afloat in the northern bunkers of Mourillon.

[52] Already having put to sea from Brest on 17 June 1940, the commander of Casabianca had to choose between scuttling his boat in deep waters or sailing to an Allied port to continue the war.

Because of their capabilities, the French submarines were principally used by the Allies for missions involving information gathering, and the loading or unloading of personnel or material.

[56] Casabianca, the only operational Redoutable-class submarine during most of 1943, carried out seven of these types of missions between December 1942 and September 1943, principally off Italian-occupied Corsica.

On 9 June 1944, Casabianca attacked a German submarine chaser with her deck gun and torpedoes off Cape Camarat, but was unable to seriously damage the vessel.

[66] In December 1942 an accord was reached between U.S. and French authorities for the transfer, one by one, of the Redoutable-class submarines to the United States for refitting and modernization, given that their design was by now almost twenty years old.

[73] During the night of 13 and 14 July Archimède was spotted by a Wassermann radar off Cape Dramont and chased by three anti-submarine patrol boats for three hours.

[76] After the return of Casabianca and Argo to the Mediterranean during the spring of 1945, the five Redoutable-class submarines passed the remainder of the war carrying out training exercises at Oran, while awaiting a transfer to the Pacific.

[79] Following their trials, they were based at Brest in January 1947, then carried out a four-month cruise off Africa in company with U-2518, a former German Type XXI submarine transferred to the French Navy in order to assess her capabilities.