French submarine Thermidor

Thermidor was one of 18 Pluviôse-class submarines built for the French Navy (Marine Nationale) in the first decade of the 20th century.

Design and description
The Pluviôse class were built as part of the French Navy's 1905 building program to a double-hull design by Maxime Laubeuf. Thermidor differed from her sisters as she was built to test the hull shape planned for the following Brumaire-class submarine. She had an overall length of 52.15 m, a beam of 5.42 m and displaced 396 t on the surface and 551 t underwater. The submarines' crew numbered 2 officers and 23 enlisted men.

For surface running, the boats were powered by two 350 PS triple-expansion steam engines, each driving one propeller shaft using steam provided by two Du Temple boilers. When submerged each propeller was driven by a 230 PS electric motor. On the surface they were designed to reach a maximum speed of 12 kn and 8 kn underwater. The submarines had a surface endurance of 865 nmi at 11.6 kn and a submerged endurance of 70 nmi at 2.8 kn.

The first six boats completed were armed with a single 450 mm internal bow torpedo tube, but this was deleted from the rest of the submarines after an accident with their sister FRENCH SUBMARINE Fresnel in 1909. All of the boats were fitted with six 450 mm external torpedo launchers; the pair firing forward were fixed outwards at an angle of seven degrees and the rear pair had an angle of five degrees. Following a ministerial order on 22 February 1910, the aft tubes were reversed so they too fired forward, but at an angle of eight degrees. The other launchers were a rotating pair of Drzewiecki drop collars in a single mount positioned on top of the hull at the stern. They could traverse 150 degrees to each side of the boat. The Pluviôse-class submarines carried eight torpedoes.

Construction and career
Thermidor, named after the second month of summer in the French Republican Calendar, was ordered on 26 August 1905 from the Arsenal de Cherbourg. The submarine was laid down in 1906, launched on 3 July 1909 and commissioned on 13 July 1910.

On 10 June 1913, Thermidor collided with the submarine FRENCH SUBMARINE Watt while Watt was moored at a wharf at the Brest Arsenal in Brest, France. Both submarines suffered damage, particularly Watt, which sustained a gash over 40 cm in length in her external port ballast tank that required a substantial period of time to repair.