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 Chacal and L'Adroit classes (commissioned 1926 to 1931). The later Guépard and Le Fantasque class destroyers (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 Mogador class destroyers 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 Scharnhorst and the Bismarck battleship classes, and the 152 mm/55 Model 1934 or 1936 on the Littorio class battleships.
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 North Carolina and South Dakota class battleships, Essex class aircraft carriers, 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 Dido class cruisers, 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 HMS Anson, 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.
Read more about this topic: Dunkerque Class Battleship, Design, Armament
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