Main Artillery
The quadruple arrangement had been foreshadowed in the French Normandie and Lyon class battleship projects, just before World War I. The all-forward main artillery arrangement had been first introduced by the Royal Navy on the Nelson class battleships, 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 Richelieu class battleships 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 Nelson class battleships.
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 Nelson class battleships supported barbettes for three-406 mm gun turrets. The 1911 French designers of the Normandie battleship class 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 HMS King George V class battleships, which had a 34 m beam. On Dunkerque and Strasbourg, as later on in the Richelieu 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 Richelieu.
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 Littorio. 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 Deutschland class shell (300 kg), or of the Scharnhorst 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.
Read more about this topic: Dunkerque Class Battleship, Design, Armament
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