Dunkerque class French super-dreadnought fast battleships
The Dunkerque class consisted of two ships built to counter the threat from the new German Deutschland class 'pocket battleships'. Since the German vessels were themselves quite small, the Dunkerque class were well within the constraints of France's commitments under the Washington Naval Treaty (France was allowed 70,000 tons (i.e. two 35,000 ton ships) but the Dunkerque class ships were only 26,500 tons each).
Eight 13-inch guns were carried and like the British Nelson class the Dunkerque's concentrated all of their main armament forward in a small area. Taking this concept one stage further than the British, the Dunkerque's were the first battleships with their main armament mounted in quadruple turrets, saving more weight than using twin or triple turrets (1,700 tons lighter than four twin turrets). This layout enabled the Dunkerque's to bring all their main armament to bear ahead while closing on a target, but at the total expense of rearward fire. So as to reduce the danger of one hit destroying all the main armament, the turrets were not placed so close together that 'B' turret's barrels hung over the roof of 'A' turret.
The French had intended to use quadrupole turrets in battleships before in the Normandie and Lyon class designs, but none were completed due to the strains of the First World War.
The Dunkerque class battleships adopted an all-or-nothing principle for their armouring in order to provide the maximum armour of the minimum weight. By placing all the main armament together a smaller area had to be armoured to protect the magazines. The ends of the ship were left un-armoured. Overall, armouring was designed to withstand German 11-inch guns.
The interesting features of the ships did not stop at the main armament. The increasingly important role of aircraft was recognised in the design, with a secondary armament of sixteen dual-purpose 130mm guns which could be used for anti-aircraft as well as anti-ship defence. Twelve of which were mounted in three quadruple turrets. For the first time ever an aircraft hanger was included as an integral part of the original battleship design to house reconnaissance aircraft. Also, there was a control tower made up of three separate structures (together weighing over 86 tonnes (85 tons)) that all rotated individually about a common axis.
The Dunkerque's may have been scaled down compared with battleships in service and building with other navies at the time, but they were superior to the German ships they were intended to counter. By opting for a lighter main armament an impressive top speed was attained whilst keeping a balanced design. Unlike battle-cruisers which sacrificed armour to attain speed simultaneously with carrying the heaviest possible armament.
Strasbourg was slightly different to Dunkerque in having the conning tower integrated with the rest of the forward superstructure and also having a range-finder mounted higher in the superstructure.