They were the first French battleships built since the Bretagne class of pre-World War I vintage, and they were heavily influenced by the Washington Treaty system that limited naval construction in the 1920s and 1930s.

French battleship studies initially focused on countering fast Italian heavy cruisers, leading to early designs for small, relatively lightly protected capital ships.

But the advent of the powerful German Deutschland-class cruisers proved to be more threatening to French interests, prompting the need for larger and more heavily armed and armoured vessels.

Wary of another naval arms race similar to the Anglo-German race that was seen as contributing to the start of World War I, the world's major navies held the Washington Naval Conference in 1921 to discuss controls on battleship construction, both to limit their size and armament but also to limit the number of ships that could be built.

[2][3] In 1926, the Chief of the Naval General Staff, Admiral Henri Salaun, requested a new capital ship design with a displacement of 17,500 long tons (17,800 t), intended to counter the new generation of Italian heavy cruisers.

[5] Design studies continued after the London Naval Treaty, where the British had unsuccessfully pushed for reductions in the maximum displacement and gun calibre.

By this time, Germany had finally begun building the first of the Deutschlands; this led to renewed concerns over the level of armour protection, which was still too thin to defeat the German 283 mm gun.

[7] The Dunkerque-class ships' relatively small size and light armament and emphasis on speed rather than protection, especially compared to the other treaty battleships of the period, has led some to classify them as battlecruisers.

For use while in port, three 400 kW (540 hp) diesel generators were fitted, and these were located in a separate room below the ammunition magazines for the main battery.

To reduce the risk of a single shell hit disabling all four guns, the turrets were divided by an internal bulkhead, and they were spaced 27 m (89 ft) apart.

Fire control equipment for the anti-aircraft battery consisted of four 1 m (3 ft 3 in) rangefinders, two forward on the tower and two on the aft superstructure.

The directors were used to gather range, bearing, and inclination data, which was then sent to a central control station below the armour decks; there, plotting tables and analog computers were used to calculate firing solutions for the guns.

[19][21] Defence against underwater attacks—torpedoes and naval mines—came in the form of layered torpedo bulkheads that incorporated liquid-filled voids to absorb blast effects.

In addition, a rubber-based compound referred to as ébonite mousse was used to help absorb the impact and control flooding in critical areas.

Where the system had to be narrowed, abreast the forward and aft magazines, the main bulkhead increased in thickness to 40 and then 50 mm to account for the reduction in effectiveness.

While Dunkerque was under repair at Toulon in 1942, consideration was given to replacing her aviation facilities with additional 37 mm guns to improve her anti-aircraft defences, but this work was not begun before the fleet was scuttled in November.

During another refit from January to April 1942, Strasbourg's forward 37 mm mounts were moved from her forecastle to the weather deck, as they were on Dunkerque, and she received an air-search radar set with four antennae.

As tensions rose with Germany over the latter's aggressive demands on Polish territory, the British and French naval commands agreed to divide responsibilities for joint operations in the anticipated war; France would cover Allied shipping in the central Atlantic, and for this purpose, Dunkerque and Strasbourg were assigned to the new Force de Raid (Raiding Force) to hunt down German commerce raiders.

[27][28] With the outbreak of war in early September, the Force de Raid, under the command of Vice-amiral d'Escadre (Squadron Vice Admiral) Marcel-Bruno Gensoul, went to sea when reports indicated that the German Deutschland-class cruisers had sortied to attack Allied shipping.

The German raiders were still in the North Sea, however, and so after meeting a French passenger liner, the Force de Raid returned to port.

Dunkerque carried a shipment of part of the Banque de France's gold reserve to Canada and then escorted a troop ship convoy to Britain in December.

Consideration was given to sending them to support the Norwegian Campaign in April 1940, but Italy's increasingly hostile posture forced the French to keep them in the Mediterranean.

[31] The British government, incorrectly fearing that the Germans intended to seize the French fleet and employ it against Britain, embarked on a campaign to neutralise the vessels.

Upon learning that the ship had not been permanently disabled, the British returned and launched an air strike from the carrier HMS Ark Royal, for which Gensoul and Dunkerque's commanders had failed to erect defences, either in the form of torpedo nets or manned anti-aircraft guns.

Those hits led to a secondary explosion of that vessel's depth charges that amounted to an equivalent of eight aerial torpedoes, which caused extensive damage to Dunkerque's hull.

In September 1940, the ship and several cruisers sortied to cover Provence, which had been repaired and refloated after the attack on Mers-el-Kébir, as she returned to Toulon.

Heavy fighting between British and Italian forces during the Mediterranean Campaign delayed Dunkerque's return to France until February 1942.

[37] Following Operation Torch, the Allied invasion of French North Africa on 8 November, Germany launched Case Anton in retaliation, moving to seize all of the so-called "Zone libre", the part of Vichy France that had up to that point remained unoccupied.

[38] Italy received control over most of the wrecks, as Germany had little interest; the Italian fleet sought as many vessels as possible, but Dunkerque and Strasbourg were too badly damaged to be repaired quickly, and so they wrote them off as a total loss.

To prevent the French from repairing them in the future, the Italians inflicted further damage on the wrecks, including cutting their main-battery guns.