Genesis of the Dunkerque
The ships of the Dunkirk class (Dunkerque and Strasbourg) were the first French battleships launched since the Great War. Following the 1922 Treaty of Washington, and the Treaty of London (1930), France took advantage of the tonnage allocated to France in terms of line vessels, cruisers, etc., making a compromise to allow more vessels in the allocated tonnage (although criticized at the time for the sake of defending the Empire).
Despite the anger upon this apparent downgrading of the French Navy, the exhausted country was in not way able to fulfill the rearmament alternative plan, more so, the spectre of pre-1912 young school era mistakes was still looming over the admiralty. In fact the fleet born from these events was coherent, modern, and probably the best the country ever had for decades. The Dunkerque class was like a symbol of it.
US Navy Recognition plates of the Dunkerque
Development of the new French Capital ship
First off, the Washinton ten years moratorium could have prevented the French and Italians to built any ships before 1932. But given the fact both accepted a reduction in size (especially the French), a derogatory measure was approved; France and Italy were allowed to replace two old battleships after 1927. This allowed considering many designs from then on. However, the new Dunkirk were not battleships nor really true battlecruisers (for this budget protection was entirely sacrificed to speed), but a compromise between the two.
Also, both countries concentrated on modernizing their old battleships and keep their allocated replacement capital ship tonnage of 70,000-long-ton to design brand new ships, with a choice of either two 35,000 tons ships but also three 23,000-long-ton (23,369 t) or four 17,500-long-ton (17,781 t) ones, which were in the latter case interested “pocket battlecruisers” (see below).
In fact all these cases were carefully examined by th admiralty in turn. For example when in 1925 the Italians launched their Trento-class cruisers, French Vice Admiral Henri Salaun considered the building of such 17,500 tons large cruisers, armed with two quadruple turrets with a seemingly obsolete caliber, 12 inches (305 mm) all forward.
They would have been capable of 34 to 35 knots and with a partial armoir able to defeat 8 in (20mm) calibers shells (those of the Trento). Next, three 37,000-ton battlecruisers designs were drawn in 1927-1928. One show a very enlaged Suffren-class cruiser 254-metre (833 ft) long, the same tripod foremast but this time three quadruple 305 mm turrets, two in chase (fore), one in retreat (aft) plus eight single 90 mm Mle 1926 HA guns and some 37mm AA artillery and torpedo tubes, 220 to 280 mm armour and 33 knots.
The second, 1928 alternative design called for a capital ship armed with three twin 406 mm turrets and four quadruple 130 mm turrets which was more capable of dealing with other battleships. It was shorter at 235 metres but wider, armor was thicker but the powerplant was smaller, thus reducing the top speed to 27 knots. However the choice was easy to make as there was no dock large enough to build a 35,000-ton hull longer than 250 metres (820 ft) at that time. In fact building the required docks would have cost the same as the two battleships, just when more stringent naval restrictions were discussed.
The last chapter of this development came when the new chief of staff of the Marine Nationale, Vice Admiral Violette, ordered the Service Technique des Constructions Navales to design a modern “amoured cruiser” which ended as a 23,690 tons ship with a triple and quadruple turrets forward and one triple aft, all armed with the same 12 in caliber but protected with 8 in plates only.
They were to be also armed by four twin 138 mm mountings and eight twin 100 mm AA turrets and 29 knots fast and a general appareance which recalled the Algérie. In fact the design had the most influence over the Dunkerque proper development.
Armour scheme of the Dunkerque class
Final displacement choice and the Deutschland class
What really decided the admiralty for good was the threat of Reichsmarine’s “pocket battleships” recently launched of the Deutschland class. Both ships “cheated” over the 10,000 tons Versailles treaty limit. They were superior to any cruiser yet fast enough to escape battleships.
It was like a reinvention of the battlecruiser concept and perfectly suited for commerce raiding. Only three ships back then were able to catch these, the British battlecruisers Hood and the two Renown class. There were doubts also to the will or capacity of the Royal navy to protected French colonial routes in case of war with Germany. So new designs were immediately scrambled to deal with the new situation and protection against German 280 mm shells was at the center.
With the choice of a speed of 30 knots, the final design displacement was a relatively easy choice: 23,000 – 25,000 tons, which fitted British limitations and allowed to built three capital ships for the allocated tonnage. Although the London 1930 treaty prolongated the “battleship holiday” to 1936, the Washington’s derogatory measure still applied and negociations took place between France and Italy in regards of their respective plans.
Their bilateral discussions ended in March 1930 with the acceptance of building only tow 23,333 ton battleships until 1936. The French had from then free hands for the Dunkerque. Their new design was quickly drawn, with a size of 213 m by 27.5 m to fit in the existing dockyards, capable of a speed of 30 knots with a 230 mm armored belt, and two quadruple 305 mm/55 gun turrets forward. However after a parliament submission it was rejected.
By 1931 Admiral Durand-Viel became C-in-C and reworked the design for a new submission: This time, tonnage was augmented to 26,500 tons and the hull slighly larger to accomodate a caliber capable of dealing with italian ships, 330 mm/50 caliber guns. Armor was also slightly increased, and an additional 130 mm DP turrets were procured. As such, the design was accepted in 1932 and the Dunkerque was ordered on 26 October and laid down on 24 December at the Arsenal de Brest shipyard.
The choice of the main artillery
The last unfinished battleships built by France were the Normandy class (1915), followed by the Lyon class. Both had in common a main artillery in quadruple turrets, but in separated pairs. The solution, unique to France, made it possible to maximize protection of vital parts related to artillery and ammunition supply.
The Lyon class, with their four quadruple turrets, would have had 16 pieces for their main artillery, a world record for a battleship. The weight of these turrets was not negligible either. However in the new tactical developments post-Jutland the advantage favored hunting fire, which explains the original chosen solution of the front artillery for the Dunkirk class, whose genesis went back to 1925 and the British Nelson class that showed the way.
Dunkerque in 1938, src: ONI203 booklet for identification of ships of the French Navy, Nov. 1942
Italian’s replica to the Dunkirk
However, when these ship’s construction was well advanced, Italy announced the construction of the Litorrio, in response to Dunkirk, with armor this time equivalent to their main artillery.
As a result, plans were made for the next class, the Richelieu to answer them in turn, to which the Italians replicated during ww2 with the Roma class. The two Dunkirks stemmed from a reflection on the usefulness of battleships, since no major naval battle had a lasting impact on strategic level, the latest being that of Jutland. In general all naval battles of WW1 with few exceptions have been battlecruiser engagements.
Also the defense of trade links in the French colonial Empire seemed to be paramount, and cruisers have always been considered better suited to this task. These ships were therefore designed specifically for this purpose. Even after the release of the heavier Scharnhorst, their artillery and armor remained nearly adequate. The Dunkirk was launched in 1935 and her sister-ship Strasburg in 1936. They were in operation in 1936-37.
Design of the Dunkirk, in detail
Dunkerque, stern view 1940 – ONI, USN Identification group Nov. 42.
Their peacetime career was already full of squadron exercises. They were based in Toulon, and regularly anchored in bases in Africa. During the conflict, the two ships chased German raiders in the south Atlantic, including KMS Graf Spee (they had been specifically designed to cope with), and protecting merchant traffic, especially the most vital roads.
Strasbourg underway, side view – Src ONI203 booklet for identification of ships of the French Navy Nov. 42
In December 1939, Dunkerque took the gold reserves of the Bank of France to Canada. The Atlantic task force force, based in Brest and formed by these ships and heavy cruisers and destroyers, was transferred in the Mediterranean in the light of the changing attitude of Italy in June 1940. They were now based at Mers el Kebir, Algeria.
Mers El Kebir
It was there, in July, following the defeat on the mainland and armistice, that they were attacked by the Royal Navy following the end of Admiral Sommerville ultimatum and ending of a parley between the two admirals. As a result of this attack, the Strasbourg was able to sail, replied at the British and was chased by the Hood and Ark Royal’s planes. She managed to escape and returned to Toulon. The less fortunate Dunkirk took 4 hits of 15 inches, destroying among others its electrical installation. She had to be towed to the other side of the harbor, out of harm. But she was attacked later by Swordfish torpedo bombers, was badly damaged and sank. She would be raised later towed to Toulon for extensive repairs, only to be scuttled with her sister-ship in Toulon in November 1942…
Strasbourg after being bombed by US Navy Aviation 1944 in Toulon harbor, USN reconnaissance 18 August 1944 (cc)
Displacement: 26,500 t. standard -36,380 t. Full Load
Dimensions: 215.10 m long, 31.10 m wide, 8.7 m draft.
Machines: 4 propellers, 4 Rake turbines, 6 Indret boilers, 135,600 hp. Maximum speed 31 knots.
Armour: 225-280 mm belt, 30 mm anti-torpedo partitions, 115-137 bridge, 330-360 mm turrets, 330 mm bunker.
Armament: 8 pieces of 330 mm cal.50 (Model 1931), 3×4 + 2×2 pieces of 135 mm DP, 5×2 pieces of 37 mm AA, 8 ML of 13.2 mm AA, 4 Loire 130 seaplanes.
Links, sources, read more
Conways all the world fighting ships 1921-1947
Author’s illustration – The Dunkerque (“Dunkirk”) at Mers-el-Kebir, July 1940
Spectacular photo of the Strasbourg after the Toulon scuttling, with the port still burning – Anonymous, released under CC licence.