French battlecruiser proposals

In the Naval Law of 30 March 1912, the French Navy called for a total force of 20 capital ships to be built by 1920. The Technical Branch subsequently issued a set of somewhat vague requirements for battlecruiser designs. The requirements stipulated a displacement of 28,000 metric tons (28,000 long tons; 31,000 short tons), a speed of 27 knots (50 km/h; 31 mph), an armament of eight 340 mm (13.4 in) guns, and a crew of not more than 1,200 officers and enlisted men. These figures were very similar to the British Lion-class battlecruisers then under construction. Numerous proposals were submitted to the Technical Branch, but only two were evaluated further. The first was prepared by P. Gille, a naval engineer overseeing the construction of the Normandie-class battleship Flandre, and the second by then-Lieutenant Durand-Viel, a student at the Naval College. As the proposals were only design studies, none were authorized and no ships were built; the outbreak of World War I ensured that even more advanced projects, like the Normandie and Lyon-class battleships were canceled as resources were redirected toward more pressing needs.^[1][2][3]

In 1911, Gille went to Britain to observe the construction of the new Orion-class battleships and the Lion-class battlecruisers. The latter ships prompted Gille to decide the French Navy ought to build battlecruisers as well, since Britain and Germany had already begun acquiring them, and they would prove useful as a fast division of the French fleet. Gille decided that his proposed ship would need a top speed of 28 to 29 kn (52 to 54 km/h; 32 to 33 mph) to retain an advantage over foreign battleships, the latest of which had estimated speeds of 22 to 23 kn (41 to 43 km/h; 25 to 26 mph). They would also need enough armor and a main battery powerful enough to fight in the line of battle. The limitations that weight imposed on the design, however, restricted the amount of armor possible, and so the traditional French practice of armoring the entire side of the ship would be impossible.^[4]

Gille's battlecruiser design called for a displacement of 28,247 t (27,801 long tons; 31,137 short tons) on a hull that was 205 meters (673 ft) long between perpendiculars, with a beam of 27 m (88 ft 7 in) at the waterline and an average draft of 9.03 m (29 ft 8 in). The freeboard forward was 7.15 m (23 ft 5 in), and aft was 4.65 m (15.3 ft). The hull lines of the ships proved to be highly efficient in tank tests during the design process. Due to the extreme weight of the main battery turrets at the bow and stern, the hull had to be strengthened to handle the strain. Very strong longitudinal bracing was incorporated, and the inner and outer skins of the hull was thickened to reinforce the bracings. The ships' expected metacentric height was 1.03 m (3 ft 5 in), comparable to the British Lion class. Each ship would be crewed by 41 officers and 1,258 enlisted men.^[5]

The ships would have been equipped with four sets of steam turbines rated at 80,000 shaft horsepower (60,000 kW) powered by fifty-two coal-fired Belleville boilers. Each propeller shaft was connected to a high-pressure turbine, a medium-pressure geared turbine, and a low-pressure turbine for forward steaming, and a direct drive turbine for steaming in reverse. The ships' top speed was to have been 28 knots. The ships would have been supplied with 2,833 t (2,788 long tons; 3,123 short tons) of coal and 630 t (620 long tons; 690 short tons) of fuel oil for supplementary oil firing. At maximum speed, the ships could have cruised for 1,660 nautical miles (3,070 km; 1,910 mi); at 20.3 kn (37.6 km/h; 23.4 mph), the range increased to 4,240 nmi (7,850 km; 4,880 mi), an at a more economical 15 kn (28 km/h; 17 mph), the range grew to 6,300 nmi (11,700 km; 7,200 mi).^[1][5]

The ships' main armament was composed of twelve 340mm/45 Modèle 1912 guns in three quadruple turrets, the same as in the contemporary French battleships of the Normandie class. One turret was placed forward, and the other two were placed in a superfiring pair, all on the centerline.^[1][5] The guns had a range of 16,000 m (17,000 yd) and had a rate of fire of two rounds per minute. The shells were 540-kilogram (1,190 lb) armor-piercing rounds and were fired with a muzzle velocity of 800 meters per second (2,600 ft/s).^[6] A secondary battery of twenty-four 138.6 mm /55 Modèle 1910 guns mounted in casemates was planned for defense against torpedo boats.^[1][5] These guns fired a 36.5 kg (80 lb) shell at a muzzle velocity of 830 m/s (2,700 ft/s).^[7] The armament was rounded out by six torpedo tubes of undetermined diameter, all submerged in the ships' hulls.^[1][5]

The armor protecting both the main armored belt amidships and the main battery turrets was 270 mm (10.6 in) thick. The lower armored deck was 20 mm (0.79 in) thick, with 50 mm (2.0 in) of armor plating on the sloped sides. The casemate guns were protected with 180 mm (7.1 in) of steel armor. The ships were also equipped with a 20 mm thick torpedo bulkhead.^[1][5]