caliber to to keep pace with the latest British battleships of the , but the French did not yet have a gun of that caliber completed, and the delays necessary to design and test it were deemed unacceptable. Additionally, the French expected to be fighting at ranges where the existing 340 mm gun was able to defeat heavy armor, so there was little need to step up to the larger caliber. The 340 mm gun was adopted, but to improve the ships' firepower, a fourth quadruple turret was added. The ships were allocated to shipyards in late 1913, with work to begin on the first two in January 1915, with the second pair to follow at an unspecified time. Work to complete the design continued into 1914, but the details of the ships' underwater protection system had not yet been finalized by the time war broke out in August 1914. With the start of the war, the project was cancelled; no work was done and no material was assembled for the vessels. Fast battleships Dunkerque class In the early 1920s, the major naval powers concluded the Washington Naval Treaty to limit battleship construction; under the terms of the treaty, France was limited to a total of of battleship tonnage. All members of the treaty system were barred from building battleships for a decade, apart from France and Italy, both of which had allotted, since their fleets consisted of older vessels. Financial weakness after the war, coupled with indecision over what type of ship to build delayed the construction of new French battleships. The navy initially conceived of small, fast battleships to counter new Italian heavy cruisers that threatened France's lines of communication in the Mediterranean. The advent of the German s, armed with guns, necessitated larger, more capable battleships, with armor heavy enough to defeat the German large-caliber guns. This process eventually produced the Dunkerque class. and were commissioned in the late 1930s; they spent the majority of their peacetime years conducting training. Following the German invasion of Poland in September 1939 that started World War II, the ships were initially used as part of the Force de Raid (Raiding Force) to hunt down German commerce raiders and to escort convoys. The ships were moored in Mers El Kébir to deter Italy from joining the war when Germany defeated France in May and June 1940, and were to be demilitarized