Dunkerque - class battleship The " Dunkerque " - class battleship was a type of warship constructed for the French Navy in the 1930s . The " Dunkerque " s were designed to counter the German pocket battleships . Their main armament was two quadruple 330 mm turrets forward , with a thick armored belt . They were smaller , with a 26 , 500 - to 27 , 300 - ton standard displacement and a smaller main artillery caliber , than the battleships authorized by the Washington Naval Treaty , but their speed was 7 knots higher than all the battleships built from 1920 to 1937 . When they were commissioned , only the last existing battlecruisers of the British Royal Navy and the Imperial Japanese Navy were their equals . Given their characteristics , they were alternatively classified as fast battleship s , small battleships , battlecruiser s , and even as " ships of the line " ( Fr . " " ) . Two ships , and , were completed . Together they formed the " 1ère Division de Ligne " ( " 1st Division of the Line " ) , and saw service during the early years of the Second World War . While they never encountered the German pocket battleships they were designed to counter , they suffered the British attack of Mers - el - Kebir , and stayed under the Vichy authorities control until they were scuttled at Toulon in November 1942 . Background . In 1922 , the Washington Naval Treaty imposed a ten - year moratorium on the construction of new battleships . But France and Italy were allowed to replace two old battleships after 1927 , for a total of 70 , 000 tons . In the late 1920s , the most powerful battleships had been designed before the Washington Treaty , and were armed with four double turrets of or diameter guns . The s , built between 1922 and 1927 with three triple 16 - inch turrets forward , were based on the 1921 G3 battlecruiser concept . The top speed was , for most battleships of the time , , although the s had top speeds , and a few under Western flags , the fast battleship s or battlecruiser s , had top speeds exceeding . But neither France nor Italy intended to build battleships that were similar to the most recent American , British , or Japanese battleships , which were very heavily armed and armored . They wished only to modernize their aging battleships , refurbishing the propulsion machinery , and upgrading the main artillery , despite the Treaty of Washington authorizing them to undertake much more radical modernizations than could the other treaty powers . In the same way , both France and Italy reserved the right to employ their replacement capital ship tonnage allocation ( ) as they saw fit , subject to Treaty limits – not only were two battleships of possible , but also three of or four of . Early development concepts . In 1925 , the first of the Italian s was laid down , and launched the following year – these ships could threaten French sea lane s between metropolitan France and colonial holdings in North Africa . In response , Vice Admiral Henri Salaun of the French Admiralty began discussing counters in 1926 and 1927 . A 17 , 500 - ton design was considered to allow four ships under the treaty limit . They would have two quadruple 305 mm ( 12 - inch ) turrets forward . The use of quadruple - gunned turrets had been planned for the cancelled and s , while the all - forward configuration was inspired by the British s . Speed would have been 34 to 35 knots , with armor to resist 203 mm shells . However , these ships were not ordered , as they could not withstand the old Italian battleships . The 17 , 500 - ton design was followed by studies for a 37 , 000 ton battlecruiser in 1927 to 1928 . A trial displacement of 37 , 000 tons was equivalent to a standard displacement of 32 , 000 to 33 , 000 tons , which was close to the treaty limit for battleships . At least two draft designs were made , showing an enlarged with a 254 m long hull , 30 . 5 m beam , and two raked funnels . The main armament fire control director was atop a tripod foremast . Armament included three quadruple 305 mm turrets ( two fore and one aft ) , eight single 90 mm Mle 1926 HA guns , twelve 37 mm Mle 1925 single AA mountings , and triple torpedo tubes . The armor belt varied from 220 to 280 mm in thickness . A hangar was behind the bridge structure , with two catapults abeam the second funnel . Power would have been from two groups of boilers and turbines , as on the , although with 12 ( rather than 8 ) Guyot - du - Temple boilers , giving a total of 180 , 000 hp and a 33 knot top speed . In 1928 , an alternate 37 , 000 - ton design emerged as a fast battleship , which had a heavier armament of three twin 406 mm turrets and four quadruple 130 mm turrets . The hull was slightly shorter at 235 m , but featured a slightly wider ( 31 m ) beam . The armor was thicker , but engine power was reduced by one - third , allowing a top speed of only 27 knots . The 37 , 000 ton battleships also did not go forward . The French Navy did not have a dock large enough to build a 35 , 000 ton hull that was longer than 250 m . For comparison , the 247 m long SS " Île - de - France " had been built at the civilian Penhoët shipbuilding yard at Saint - Nazaire . Building the required naval infrastructure would have cost the same as the two battleships , and interfered with existing building programs . Furthermore , more stringent naval restrictions were then being discussed . The Disarmament Subcommittee of the League of Nations had , by then , also turned their attention to naval limitations , and with the British pushing for a limit of 25 , 000 tons with 305 mm guns for battleships , the French did not want to jeopardize the negotiations . In 1929 Vice Admiral Violette , then Chief of Staff of the French Navy , ordered a study for a " protected cruiser " from the " Service Technique des Constructions Navales " , the department responsible for naval construction . Their design had a displacement of 23 , 690 tons with three 305 mm turrets ( one triple and one quadruple forward , and one triple aft ) , four twin 138 mm mountings ( the caliber used on the most recent destroyers ) , and eight twin 100 mm turrets for antiaircraft use ( as on , the latest heavy cruiser ) . Top speed would have been 29 knots , with the armor only able to withstand 203 mm shells . The final design resembled " Algérie " , with a distinctive forward tower with a single funnel abaft . This profile would carry over into the final " Dunkerque " design . emerges . French plans were upset when the Germans laid down the first in February 1929 . Although the cruisers secretly displaced far more than allowed by treaty , they were nonetheless well - suited for commerce raiding , and could outrun all major capital ships ( except for and the two s of the British Royal Navy ) . The French immediately prepared draft designs for a counter to the " Deutschland " s . Protection against German 280 mm shells was the paramount requirement , although it seemed that the armament from previous projects and a speed of 30 knots might still be maintained . The end displacement was between 23 , 000 and 25 , 000 tons , which fit within the limitations being proposed by Britain . The 1930 London Naval Treaty extended the " battleship holiday " from the Washington Naval Treaty until the end of 1936 , although France and Italy were allowed to lay down new battleships in accordance with the older treaty . France , however , refused to adhere to the new restrictions – mainly related to cruisers – due to new German construction . In response , Italy also refused to accept these new restrictions . Bilateral negotiations between France and Italy took place in early 1931 to resolve the issue , and resulted in an agreement on 1 March that allowed each country to build only two 23 , 333 ton battleships until 1936 . It was not possible to go any further , with the Italians being dissatisfied with their 23 , 333 ton design , and also studying a 35 , 000 ton design . The French did decide to go forward with 23 , 333 tons as a compromise between an inadequately armored 17 , 000 ton ship and a prohibitively expensive 35 , 000 ton ship . The design was 213 m long with a 27 . 5 m beam , and was armed with two quadruple 305 mm / 55 caliber turrets forward and three quad 130 mm Dual Purpose turrets aft . It had a 230 mm armored belt with 150 mm horizontal protection , and was designed for a speed of 30 knots . This was submitted to Parliament in May , but was rejected after two months of debate – it seemed excessive to counter the ( official ) 10 , 000 ton " Deutschland " with a ship of twice that size . In July , the navy was allowed to carry out revisions for resubmission . Vice Admiral Durand - Viel became Chief of Staff in January 1931 . He ordered a study replacing the 305 mm / 55 guns with 330 mm / 50 guns so as to outmatch the old Italian battleships . This increased displacement ( by 3 , 000 tons ) to 26 , 500 tons , length by 2 meters , beam by 2 . 5 meters , and reduced speed to 29 . 5 knots . Two more double 130 mm DP turrets were added , and the thickness of the armored belt and decks were also increased slightly . This design was approved by Parliamentary committees in early 1932 . The was finally ordered on 26 October , and laid down on 24 December . Responses to " Dunkerque " . The Germans response to " Dunkerque " were the , both laid down in 1935 . They were larger and better armored , but had only nine 280 mm guns . These guns were improved versions of the type used by the " Deutschland " class , with longer barrels and higher muzzle velocity . A heavier armament had been pre - empted by negotiations for the 1935 Anglo - German Naval Agreement . As the " Dunkerque " - class ships were designed to withstand 280 mm shells , the French saw no need to reply with a new class . Rather , it was the Italians who provoked the next class of French capital ship . On 26 May 1934 , Duce Benito Mussolini announced that Italy would exercise its treaty right to build new battleships – this was confirmed a few days later when Agenzia Stefani reported the laying down of two 35 , 000 ton s . The French almost immediately ( on July 16 ) ordered a second " Dunkerque " , the , with increased vertical armor . She was laid down in November . Also in the meantime , the French began work on their own 35 , 000 - ton design , which would emerge as the . Design . " Dunkerque " was an innovative design , notable for concentrating the main armament of eight 330mm / 50 Modèle 1931 gun s forward . As built , had a standard displacement of 26 , 500 t , a 215 m length , a 31 m beam , and a 8 . 5 m draught . Her propulsion machinery developed 107 , 000 shp , allowing a speed of 29 . 5 knots , with the armor belt at a maximum thickness of 241 mm ( 9¾ - inches ) . was the same except for heavier vertical armor , with a displacement of 27 , 320 t , and 0 . 15 m more draught . " Dunkerque " bore distinct similarities to the battlecruiser , which was discarded in February 1932 due to the London Naval Treaty . This explains why Henri Le Masson considered the " Dunkerque " ships as being closer to battlecruisers than to battleships . The British battlecruiser had eight 34 . 3 cm Mk V gun s , a length , a beam , a draught , and 108 , 000 shp for 29 knots . " Dunkerque " differed mainly by having an all - forward main artillery arrangement ( which saved 27 % on turret armor ) , and a more modern propulsion plant . This allowed the French ship to have 10 cm more armor ( 330 mm versus 229 mm ) on its turret faces , and to sport horizontal armored decks . Similarities could also be seen when compared to the British s . Both classes saved weight by locating the machinery further aft to cut shaft length , and used inclined armor belts to increase their effective thickness . Both classes concentrated the secondary battery astern for superior firing arcs , and placed the main fire control atop the bridge structure . However , the two designs reflected different objectives . The " Nelson " s prioritized firepower and protection over speed , with the " Dunkerque " s being the opposite . " Dunkerque " reflected the evolution of French design , demonstrated elsewhere by the changes from the s to the cruiser . Armament . Main artillery . The quadruple arrangement had been foreshadowed in the French and projects , just before World War I . The all - forward main artillery arrangement had been first introduced by the Royal Navy on the s , but these warships had only three turrets carrying nine guns , and the angles of fire for the rearmost guns were limited by the turrets to their front , as it had not seemed possible to accept the supplementary weight of armor above the main armored deck for the barbette of a third turret in superposition of a second turret yet raised . Retained on " Dunkerque " , the two quadruple 330 mm foreturret arrangement gave unrestricted forward fire . Therefore , the entirety of the main artillery was able to fire forward , as the ship closed on her enemy , in an angle where she made the smallest possible target . When " Dunkerque " was laid down , it was more powerful than any existing German or Italian warship , and was intended to be engaged as part of a scout wing of the slower and heavier British battlefleet , so the concept of the main artillery concentrated in the bow seemed justified . Six years later opinions had changed , and the French Admiralty came back to a main artillery arrangement on the bow and the stern ( on the " Gascogne " battleship project ) , and in 1940 June , in the tactical situation of the battle of Mers - el - Kebir , this main artillery disposition was actually a severe handicap . The biggest drawback of the quadruple turret was that a single unlucky shot that immobilized one of the turrets would effectively put half the main artillery out of action . So the French quadruple turrets of both the " Dunkerque " and s were divided internally to localize damage , and this was proved effective when " Dunkerque " , at Mers - el - Kebir , was stricken by a 381 mm shell on the upper 330 mm turret , which put out of action only the right - half turret . In order to avoid the possibility of a hit which simultaneously damaged both turrets , they were positioned 27 m apart from one another - there were 19 m between the A and B turrets , and 23 m between B and C turrets , of the s . The diameter of a barbette is all the more large because of the number of turret guns and their caliber . With a 32 m beam , the s supported barbettes for three - 406 mm gun turrets . The 1911 French designers of the s had thought that it was possible to install quad 340 mm turrets on ships with a beam of 27 meters . The " Dunkerque " designers resolved that quad 330 mm turrets were the maximum possible with 31 m beam . Nevertheless , the four barrels were not mounted independently in individual mounts because this would have meant an unduly large barbette diameter . For that reason , the right - and left - hand pair of barrels were each placed in a common mount . This was not the case on the fore and aft 14 - inch quadruple turrets of the British " King George V " - class battleships , which had a 34 m beam . On " Dunkerque " and " Strasbourg " , as later on in the and " Jean Bart " , the guns of the half turrets were so close ( 1 . 69 m ) that a " wake effect " between shells fired simultaneously by a half - turret was leading to excessive dispersal . This was not corrected before 1948 on the . The weight of one quadruple 330 mm turret built by Saint - Chamond was 1 , 497 tons , nearly the same weight as one triple 381 mm turret of the . The maximum gun elevation was of 35° , the muzzle velocity was 870 m / s , and the range at maximum elevation was 41 , 500 m , giving a relatively flat trajectory . The nominal rate of fire was one round every 40 seconds ( 1 . 5 rounds per minute ) , which could be increased to one every 30 seconds ( or 2 rounds per minute ) under ideal conditions . The turrets were intended for loading at any elevation angle , although as it occurred , shells jammed in the breech at higher elevations when the other guns were firing , and thus as a practical matter , loading took place at a 15° elevation . The rate of elevation was 6° / s , and the rate of train was 5° / s . The 330 mm shell was 1 . 65 m long and weighed 570 kg , which was nearly twice the weight of the 280 mm shell ( 300 kg ) , or of the class AP shell ( 336 kg ) . The weight of Italian battleship shells was 452 kg for the 305 mm guns , and 525 kg for the 320 mm guns , after reconstruction . The British battleships which bombed the French battleships at Mers - el Kebir fired 875 kg shells . The 330 mm shell was Armor Piercing Capped ( APC ) , registered in the French Navy as " Obus de Perforation Modèle 1935 " ( " OPf Mle 1935 " ) existing in two variants , OPf and OPfK , the later OPfK variant incorporating a dye bag and fuze ( " dispositif K " ) to color ( red in " Dunkerque " , green for " Strasbourg " ) not only their splashes but their hits , and thereby facilitating spotting for ships operating in formation while in combat . A High Explosive ( HE ) variant of shell , referenced OEA Mle 1935 ( " Obus Explosif en Acier " ) , could have been designed and tested , but would have not been ordered , as no reference of this shell has been found in the war ammunition inventories of the ships . The heavy guns caused a great deal of difficulty – when firing slightly aft of beam , the ship ' s command position was troubled by the noise of the explosion , the fire , and the smoke to such an extent that the full arc of fire could not practically be utilized . The absorption of the great recoil forces also presented difficulties , and these ships were very lightly constructed , and they suffered repeatedly from damage caused by the firing of their own guns . Secondary artillery . The secondary artillery was dual purpose , anti - ship and long - range anti - aircraft , for the first time on capital ships , as was followed by the Royal Navy on the " King George V " - class battleships . Three quadruple armored turrets ( turrets V , VI , and VII ) , weighing 200 tons , were aft , one axial ( turret VII ) on the aircraft hangar , and the others ( turrets V and VI ) laterally disposed , abeam the after superstructure . Like the 330 mm turrets , the quad 130 mm turrets had a 20 mm steel bulkhead dividing the turret in two independent half - turrets , in which the two guns were placed on the same mount with distance - apart gun axes of 0 . 55 m . The two double turrets ( turrets III and IV ) amidships had only 20 mm anti - splinter plating . In the anti - surface mode , the 130 mm guns were firing 33 . 4 kg Semi Armored Piercing ( SAP ) shells ( referenced in the French Navy as OPfK 130 mm Mle 1933 ) , with a muzzle velocity of 800 m / s , out to a maximum range of 20 , 800 m at an elevation of 45° , against aircraft , and 29 . 5 kg time - fused HE shells ( OEA Mle 1934 ) with a muzzle velocity of 840 m / s , with a ceiling of about 12 , 000 m at the maximum elevation of 75° . The rate of fire was 10 – 12 rounds per minute . The maximum training speed was 12° / s , and the maximum elevating speed was 8° / s . However , these guns didn ' t have sufficient power for their anti - ship mission . The 130 mm ( 5 . 1 inches ) guns had been used in single mountings ( Mle 1919 and 1924 ) , as an anti - ship battery on the destroyers of the and classes ( commissioned 1926 to 1931 ) . The later and s ( commissioned after 1929 ) , however , were fitted with stronger 136 . 8 mm ( 5 . 5 inch ) guns , also in single mountings ( Mle 1923 and Mle 1927 ) , and the 1929 « protected cruiser » project was designed with anti - ship 138 . 6 mm LA guns , in dual mountings , which were actually installed ( Mle 1934 ) for the first time on the s in the late 1930s . The Axis navies ( Kriegsmarine and Regia Marina ) fitted their battleships with distinct batteries for anti - ship and anti - aircraft purposes , preferring the 150 mm caliber for the anti - ship artillery on the and the s , and the 152 mm / 55 Model 1934 or 1936 on the . In the anti - aircraft mode , the 130 mm Mle1932 guns were considered to have poor efficiency against close - rapid aircraft ( i . e . dive bombers ) due to its too - slow rate of fire of 10 rounds per minute . The US Navy and the Royal Navy opted for dual - purpose batteries , and chose calibers equivalent to the French 130 mm caliber – slightly less , 127 mm ( 5 inch ) for the US Navy , or slightly more , 133 . 3 mm ( 5¼ inch ) for the Royal Navy . The US Mark 12 127 mm / 38 caliber gun – used in dual mountings on the and battleships , s , and many cruisers , had a higher rate of fire of 15 rounds per minute ( and even 22 rounds per minute during short periods ) , but it was usually under the control of the advanced Mark 37 Gun Fire Control System , which provided accurate and timely firing solutions against both surface and air targets . The Royal Navy 133 . 3 mm Dual Purpose guns , first used on the " King George V " - class battleships and later on in the s , originally had characteristics equivalent to the French 130 mm guns , but they were found reliable only on the last unit of the " King George V " battleship class , the , and on the " Bellona " sub - class cruisers , after they were linked to the improved RP10 and RP10Mk2 fire control , which increased training and elevating speeds to 20° / s , and with the High Angle Control System in its best performing versions . " Dunkerque " - class battleships were also the first French capital ships to have Remote Power Control ( RPC ) for training and elevating on the main and secondary turrets , but the Sauter - Harlé - Blondel RPC training gear proved unreliable , and the system never worked properly . A so - called " « electromagnetic detection device » " , the French ancestor of radar , were to have been fitted on the " Strasbourg " in 1942 , as on the " Richelieu " as early as 1941 , and also on the " Jean Bart " , but only for sea and air warning , and not as a gunnery fire - control radar . Anti - aircraft artillery . With five 37mm CAD Mle 1933 semi - automatic mountings and eight 13 . 7 mm machine guns in quadruple mountings , these ships lacked the numerous quick - firing light artillery that was mounted on the " Richelieu " during her refit . The 37 mm / 50 guns were frequently used as light anti - aircraft batteries on the French Navy warships in the late 1920s . In the single mount CAS Model 1925 , they were fitted on the 10 , 000 ton heavy cruisers and destroyers . Hand - loaded , using 6 - round box magazines , and even in the twin semi - automatic CAD Model 1933 , the rate of fire – which was intended to be 20 to 30 rounds per minute – was practically only of 10 to 15 rpm . This appeared to be too slow as compared to the rate of fire of guns of equivalent caliber , such as the British Pom Pom gun or the Swedish designed Bofors 40 mm / L60 gun , the rate of fire of these being between 120 and 200 rpm . To address such issues , it was decided to develop a new gun 37 mm / 70 Model 1935 , with an automatic AA twin mount ( ACAD Model 1936 ) , linked with one fire control director ( or two mountings for one fire control director ) . The intended rate of fire was 165 to 172 rpm . The development of this gun and its twin automatic mounting proved to be more difficult than was thought , and thus it appeared that it would not be possible for the " Dunkerque " to be fitted with these before her completion . During her trials , " Dunkerque " received only six 13 . 2 mm / 76 quadritube Model 1929 Hotchkiss mountings ( amidships and abeam tower ) . At the time of completion , she was fitted with six single 37 mm CAS Model 1925 mountings , which were replaced in early 1939 by four twin semi - automatic 37 mm CAD Model 1933s ( two abeam turret II and two between the funnel and the aft tower , with four directors , two above the fore pair of 37 mm mountings , and two just before the second pair ) . A fifth 37 mm CAD Model 1933 was added in August 1939 on the " Dunkerque " , located abaft the 130 mm quad turret VII ( centerline aft ) . " Strasbourg " received only four twin 37 mm semi - automatic CAD Model 1933 mountings , and instead of the fifth twin 37 mm mounting , received a quadruple 13 . 2 mm MG mounting . Fire control . A massive fore control tower was , for the first time , fitted with an internal lift and topped by three conductors ( numbered n°1 , 2 , and A from top down ) , which were mounted on the same axis . The accumulation of heavy weight ( 85 tons ) so high up in the top was felt to be noteworthy . When " Dunkerque " was torpedoed at Mers - el - Kébir on 6 July 6 , 1940 this proved to be a shortcoming , as the main fire control directors were unseated from their ball races because of the " whiplash " effect on the mast around which they were mounted . A secondary control tower , topped by two conductors ( numbered n° 3 and B ) , was also positioned abaft the funnel . Range finding . For the 330 mm battery , there was a stereoscopic triplex 12 m OPL ( " Optique de Precision de Levallois - Perret " ) rangefinder , which was replaced in 1940 by a 14 - meter model , in director A . This system weighed 40 tons , and was placed in a lower position atop the fore tower . A stereoscopic duplex 8 m OPL range finder in director B was located in a lower position atop the aft tower , while two stereoscopic duplex 12 m OPL range finders were located one in each main artillery turret . For the 130 mm battery , there was a stereoscopic duplex 6 m OPL range finder for the anti - ship gunnery in director 2 which weighed 25 tons in a central position , and a stereoscopic duplex 5 m OPL range finder for the anti - aircraft gunnery in director 1 which weighed 20 tons in an upper position , both atop the fore tower , and a stereoscopic duplex 6 m OPL range finder for director 3 was located in an upper position atop the aft tower , with three stereoscopic duplex 6 m OPL range finders , one for each quad 130 mm turret . In addition to the main gunnery directors , a stereoscopic OPL 5 - meter tactical rangefinder ( to be used by the flag staff ) was located atop the conning tower of " Dunkerque " . On " Strasbourg " , it was located atop the fore tower , and the silhouette slightly different , as it integrated the conning tower and the bridge installations . Watch . For the optical watch , at the lower level ( " veille basse " ) , for close sea targets , there were three lookout positions port and starboard , on the first deck abeam the bridge . For aerial targets , the middle lookout station ( " veille moyenne " ) was on platform 3 of the forward tower , having five lookouts on both sides of the ship . Against mines and torpedoes , the upper lookout station ( " veille haute " ) was on platform 8 of the forward tower , with five lookouts on both sides of the ship . For night firing , there were seven searchlight projectors on " Dunkerque " , four on a raised platform around the after base of the funnel , two on platform 6 on the rear of the fore tower , and one in a forward position on the same level of the tower . " Strasbourg " had six searchlight projectors , four in the same positions as on the " Dunkerque " , abaft the funnel , and two in forward positions on the fore tower . Aviation facilities . The aircraft installations ( hangar , catapult , and crane ) on " Dunkerque " were particularly complete and well - designed , and were major advances over the facilities retrofitted to older battleships in the 1920s . For example , on the fast battlecruiser HMS " Hood " , a stern catapult was fitted in 1929 , but which had to be removed in 1932 as it was frequently awash in the North Atlantic heavy seas ( due to the lack of freeboard aft ) . A single 22 m long trainable catapult was located along the center line on the quarterdeck . It was operated with compressed air , and could launch a 3 . 5 ton aircraft at 103 km / h . Adjacent to the hangar , there were workshops for repair and maintenance . The aircraft were Loire 130 single - engined flying boats . Two planes were to be stowed , wings folded , in a two - tier hangar on the two platforms of a lift , and a third on the catapult , with wings deployed , and the possibility to stow a fourth plane atop the aviation hangar . The planes were moved on rails from the hangar to an elevator , then placed on the catapult . At the end of its mission , the Loire 130 landed in the sea and taxied alongside the ship . It was then lifted aboard by a recovery crane with a capacity of 4 . 5 tons . The aviation fuel was stowed in tanks located in the upper part of the stern . These incorporated certain safety features , including refrigeration and sprinkler systems and the replacement of used fuel by an inert gas . Armor protection . The proportion of the weight of the protection , relative to the design displacement , reached 35 . 9 % in the ship , which was the highest value recorded until then ( the armor weight was only 34 % of design displacement on the s ) . The protection design in the class was also very modern , as it used the " all or nothing " armor scheme , unlike contemporary German warships . The citadel , being about 126 m long , corresponded to about 60 % of the ship ' s length , which while very similar to the 57 % figure of the " Nelson " battleship class , left unprotected a long forward part of the ship . The French Navy Board had recommended that the second unit of the " Dunkerque " class had an improved vertical armor , and this was implemented . Thus , the protection weight on " Strasbourg " was increased by 749 tons , and reached 37 . 2 % of the normal displacement . Underwater protection . The underwater protection consisted of a " sandwich " of void spaces , light bulkheads , liquid loading compartments , compartments filled with rubber - based , water - excluding compound called " ébonite - mousse " , and a heavy internal holding bulkhead to absorb the explosion of a torpedo warhead . The compartment outboard of the inclined armor belt had a maximum depth of 1 . 5 m and was filled with " ébonite mousse " . Inboard of this compartment , there was a 16 mm bulkhead , enclosing a void compartment 0 . 9 m deep , then an oil fuel bunker 3 . 9 m deep , then a 10 mm bulkhead containing a void compartment 0 . 70 m deep , backed by a 30 mm torpedo bulkhead of special steel . Abeam the magazines fore and aft , the torpedo bulkhead thickness was increased to 40 – 50 mm , and the fuel bunkers were replaced by a same - depth compartment filled with " ébonite - mousse " . The maximum depth was around 7 . 5 meters . This figure exceeded the depth of underwater protection on existing battleships , where it was no more than 5 meters . This underwater protection proved to be effective enough when , at Mers - el - Kébir on 6 July 1940 , fourteen of the forty - four depth charges carried on the patrol ship " Terre - Neuve " , which were equivalent to 1 , 400 kg of TNT or eight air - launched torpedo warheads , exploded within a few meters of the " Dunkerque " hull . Propulsion . The speed of a warship depends not only of the power of her propulsion plant , but also her hydrodynamic characteristics , which vary with the ratio of length to beam . But the length of the ship also has consequences on the displacement , because of the weight of the hull itself , but also because of the weight of the hull armor . With a main armament of eight twin 15 - inch ( 381 mm ) gun turrets , had a 42 , 000 ton displacement , a 262 m hull , and a propulsion machinery developing 144 , 000 shp , yielding a 31 knot maximum speed . The s had a more powerful armament , but with a weight - saving arrangement of triple turrets on a shorter citadel , and stronger protection . But as her displacement was limited to 35 , 000 tons , the hull was only 216 m long , and with machinery space reduced . The propulsion plant power of 42 , 000 shp allowed only a 23 knot speed . The requirements imposed on the French designers of " Dunkerque " were different – a 26 , 500 tons displacement , allowing accommodation of an armament and a protection able to counter the fire of pocket battleships . However , a 215 m hull could be built , with its longest part ( 200 m ) , in the building dock of Brest Navy Yards and , imperatively , with a maximum speed of 29 . 5 knots . The propulsion was assured by six boilers and four Parsons turbines on " Dunkerque " . On " Strasbourg " , the boilers were built under license by the Penhoët Shipbuilding Yards . These small - tube boilers were operated at a pressure ( temperature ) of 27 kg / cm² ( 350 °C ) . They were 5 . 33 m long , 5 . 34 m high , and 6 . 50 m wide , installed two boilers side - by - side in three boiler rooms . Boiler Room 1 was underneath the fore tower , with ( from starboard to port ) boilers n°10 and n°11 , followed by the forward Engine Room housing the geared turbines for the wing shafts . Boiler Rooms 2 and 3 were adjacent beneath the funnel , with boilers n°20 and n°21 in Boiler Room 2 , and boilers n°31 and n°32 in Boiler Room 3 . The after Engine Room housing the turbines for the center shafts was abaft Boiler Rooms 2 and 3 . A 18 mm bulkhead separated the forward Engine Room from Boiler Room 2 , dividing the machinery plant in two independent units . This " unit machinery " layout was considered essential for relatively lightly - armored ships to enable them to continue operating following action damage , and was first introduced by the French Navy in the first Treaty cruiser , the . In each Engine Room there were two sets of turbines , each driving a three - bladed propeller with a diameter of 4 , 20 m , on " Dunkerque " , and a four - bladed propeller with a diameter of 4 . 045 m on " Strasbourg " . Each set comprised a two High Pressure ( 27 kg / cm² ) turbines ( HP1 and HP2 ) , a Medium Pressure ( 8 . 5 kg / cm² ) turbine , and Low Pressure forward and reverse turbines , which were linked in series with HP 1 as a cruise turbine . The ship could steam at 15 . 5 knots on two shafts , and 20 knots on four shafts , at one - quarter power , and with HP 2 being engaged at between 34 % and 50 % of maximum power . Four turbo generators of 900 kW each were distributed between the engine rooms . Designed horsepower was 107 , 000 shp , for maximum speed of 29 . 5 knots . During " Dunkerque " ' s speed trials , in May 1936 , 30 knots were sustained over eight hours , with 114 , 000 shp and 30 , 000 tons displacement , and 31 . 6 knots were reached with 135 , 585 shp forcing . In July 1938 , during the trials of " Strasbourg " , the results were similar at 30 knots while developing 115 , 000 shp , and 30 . 90 knots with 131 , 960 shp forcing . The maximum fuel load for peacetime cruising was 4 , 500 to 5 , 000 tons , but in wartime , this figure was reduced to 3 , 700 tons to maximise the effectiveness of the underwater protection system , as filling the liquid - loading compartments to the brim creates additional pressure on bulkheads , instead of absorbing the pressure of an explosion . The radius of the class was 7 , 850 nmi at 15 knots , 6 , 300 nmi at 20 knots , and 2 , 450 nmi at 28 . 5 knots . During the " Dunkerque " sea trials , it appeared that funnel smoke interfered with the use of the aft control tower rangefinders . Thereafter she was fitted ( between March and May of 1938 ) with a more important funnel cap , nicknamed as a " bowler hat " . " Strasborg " received the same funnel cowling in September and December 1938 . War service records showed that the ship ' s bow suffered damage in the rough seas of the North Atlantic winter , according to one of her Flag Officers . The German s had the same problem , particularly during the winter of 1939 to 1940 , even after they had been fitted with a reinforced " Atlantic bow " in the period 1938 to 1939 . Career . Prewar service . " Dunkerque " was laid down in the Brest Navy Yard on 24 December 1932 , in the graving dock n°4 . She was floated out on 2 October 1935 , and the ship with 17 meters missing ( as the graving dock was only 200 m long ) was towed to graving dock n°8 , where her bow was fitted . Sea trials were carried out from mid - April 1936 to late April 1937 . In mid - May 1937 , she represented France in the Naval Review of 1937 , at Spithead , Portsmouth , to mark the coronation of King George VI and Queen Elizabeth . On May 27 , a further review took place off the Isle of Sein , where the French Mediterranean and Atlantic squadrons were assembled following combined exercises . " Dunkerque " hosted there the Navy Minister and the new Chief of Staff of the French Navy , Vice Admiral Darlan . On September 1 , 1937 , " Dunkerque " joined the Atlantic Squadron as the flagship of Commander - in - Chief Vice Admiral Gensoul , and to take part in various exercises with the Atlantic Squadron in 1938 . " Strasbourg " was laid down on the n°1 slipway of the civilian Penhoët Shipbuilding Yards at Saint - Nazaire , which had been built to accommodate the 313 - meter long keel of the liner " Normandie " . She was launched in December 1936 , to be fitted out , and left Saint - Nazaire for Brest on 15 March 15 , 1938 for acceptance trials , which were carried out . " Strasbourg " entered service in April 1939 , joining the Atlantic Fleet , and formed with " Dunkerque " the " 1ère Division de Ligne " ( " the 1st Division of the Line " ) . White bands were painted on the funnel in March 1939 – a single one on " Dunkerque " ( as Division flagship ) , and with two on " Strasbourg " . After an official visit on 3 and 4 May to Lisbon ( Portugal ) for the commemoration of the discovery of Brazil by Alvares Cabral , both battleships – accompanied by three modern light cruisers of the 7 , 600 - ton type and forming the 4th Cruiser division , visited in late May and early June , Scottish harbors and Royal Navy bases , Liverpool , Oban , Staffa , Loch Ewe , Scapa Flow , and Rosyth , and returning to Brest after a four - day call at Le Havre . During the " Phony War " . In the first days of September 1939 , the " Force de Raid " – under Vice Admiral d ' Escadre ( " Squadron Vice Admiral " ) Gensoul on " Dunkerque " , and including the 1 st Line Division , the 4th Cruiser division , and eight large destroyers – was based in Brest , and sortied immediately as German « pocket battleships » were reported ( wrongly ) , to be trying to pass in the Atlantic . However , it was soon decided to split the " Force de Raid " into hunting groups against the German surface raiders , and incorporating some Royal Navy warships . In October – November 1939 Force X , under Vice Admiral Duplat , on the French heavy cruiser , with , French heavy cruiser , and the ( aircraft carrier ) was based at Dakar , and vainly undertook sweeps against the . When " Strasbourg " returned to Brest , 800 of her powder charges remained stored in Dakar . This powder was , during the battle of Dakar , used for the , and was subsequently wrongly incriminated in the explosion of the " Richelieu " s upper turret 380 mm barrels . In November and December , the and the French 4th Cruiser Division , joined to intercept , under orders of Vice Admiral Gensoul , the and the , which had sunk the Armed Merchant Cruiser north of the Faroe Islands on 23 November 1939 . As the German battleships renounced to break into the Atlantic , " Dunkerque " suffered bow damage in a huge North Atlantic storm and had to be docked for repairs . The " Dunkerque " , in December 1939 , took part in the shipping to Canada of a part of the Banque de France ' s gold reserve . Faced with the dubious Italian attitude during the spring of 1940 , the " Force de Raid " was dispatched , on 2 April 1940 , to the Mediterranean , but was ordered to return to Brest some days later to cover the Allied reaction to the German landings in Norway on 9 April 9 , 1940 . Finally , the " Force de Raid " was definitively transferred to Mers - el Kebir ( 24 April 1940 ) . Mers - el - Kébir . The only test in battle for the and the came in the attack on Mers - el - Kébir , after the fall of France , from the Force H battleships , , , and , though the French battleships had not been designed to confront these heavily armed battleships . In the late afternoon on 3 July 1940 , the surprise was terrific – strategically , the French crews did not believe , up to the last moment , that the British warships were actually going to fire on them , and tactically , because their ships were tightly moored , their guns trained towards land , and as the British warships were free of their movements , ranged at 16 , 000 m , in a high sea . As the old super - dreadnought , struck in her magazines , capsized and sank , killing nearly 1 , 000 seamen , " Dunkerque " , after painfully breaking her mooring ropes , quickly suffered four - 15 inch shell hits . The first shell rebounded off the upper 330 mm turret roof , killing all the men in the right half - turret ( the left half - turret remained operational ) . The second shell damaged the aircraft installations , and the last ones – piercing the armored belt – damaged boilers and destroyed the electric power plant . Therefore , the ship had to be moored on the other side of Mers - el - Kébir roadstead . , escorted by five destroyers , headed to the pass , only narrowly missed by the shells of the British guns . Steering east - north - east at 28 knots , she escaped the pursuit by and the Fairey Swordfish torpedo bombers of , reaching Toulon in the evening of the following day . The armored belt of the " Dunkerque " was proved unable to resist the 381 mm shells , but the damage was not as deadly as might have been feared , because the British fire ceased after less than twenty minutes , the French admiral having signaled that he had ordered his ships to cease firing . Admiral , " Amiral Sud " , Commander in Chief of the French Navy in North Africa , in a later radio message to the French Admiralty , told of « moderate » damage , and boasted that " Dunkerque " would soon be able to return to Toulon on her own steam . The British Admiralty , knowing this , ordered Admiral Somerville , the Force H Flag Officer , to attack again , to put " Dunkerque " permanently out of action . With " Dunkerque " being beached just in front of a village , and Admiral Somerville fearing that gunfire might cause serious collateral damage to civilians , an attack was launched with torpedo bombers on 6 July . Unluckily again , one of the torpedoes hit a small patrol ship moored alongside " Dunkerque " that was carrying forty - four depth charges . The explosion of fourteen depth charges ripped an enormous hole in the battleship ' s hull , and " Dunkerque " sank in shallow water . As the 330 mm magazines had been ordered to be flooded at the beginning of the air attack , " Dunkerque " escaped a total loss . The total number killed on " Dunkerque " during the two attacks of 3 and 6 July 1940 reached 210 . Scuttling at Toulon . With lost , and the and severely damaged , the interned at Alexandria , the and the seized in Great Britain , and with only four heavy cruisers ( of seven ) , and three light cruisers ( of twelve ) under Vichy control in Mediterranean waters , and with the Atlantic harbors under German occupation , a reorganisation of the Vichy French naval forces had to be carried out . The 1st ( fast battleships ) and 2nd ( slow battleships ) " Divisions de Ligne " and the Atlantic Fleet were dissolved in August 1940 , and the new " Forces de Haute Mer " ( High Sea Forces ) were created , with Admiral de Laborde appointed as Commander in Chief on 25 September 1940 . He raised his flag on after the upper part of the fore tower had to be fitted out to better accommodate an admiral ' s staff . Vice Admiral Gensoul – though he received the fifth star of a full Admiral – never got a further sea command . The " Strasbourg " , flagship of the " High Seas Forces " , nearly never even went to sea , due to the stringent restriction of fuel , but she was eventually sent to cover , in November 1940 , with four cruisers and some destroyers , the return of the " Provence " to Toulon . IN 1941 , she received three more single 13 . 2 mm Browning CAS MG , and was fitted in 1942 with a " détecteur électro - magnétique " , the French predecessor of a sea and air warning radar . In February 1942 , having been summarily repaired , the " Dunkerque " returned under her own steam to Toulon , where she was dry - docked . After the Wehrmacht had occupied the Zone libre in retaliation for the successful Allied landings in North Africa , the " Dunkerque " and the " Strasbourg " were scuttled at Toulon , on 27 November 1942 , when the Germans attempted to seize the French warships that remained under Vichy control . The " Strasbourg " , having been salvaged by the Italians and partly dismantled , was returned by the Germans to the Vichy authorities after the Armistice between the Allies and Italy . On 18 August 1944 , she was bombed and sunk by US Air Force aircraft , as the Allied forces , having landed three days previously , advanced to liberate Toulon . The " Dunkerque " was left in a very decrepit condition , and she and the wrecked " Strasbourg " were scrapped after the war .