Pluviôse-class submarine

The Pluviôse-class submarines were a group of 18 submarines built for the French Navy in the first decade of the 20th century. Before World War I, two were accidentally lost, but one of these was salvaged and put back into service. Four others were lost during the war and the survivors were stricken in 1919.

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. The submarines displaced 404 t surfaced and 553 t submerged. They had an overall length of 51.12 m, a beam of 4.96 m, and a draft of 3.15 m. FRENCH SUBMARINE 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 had a crew of 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 (FRENCH SUBMARINE Pluviôse, FRENCH SUBMARINE Messidor, FRENCH SUBMARINE Ventôse, FRENCH SUBMARINE Germinal, FRENCH SUBMARINE Floréal and FRENCH SUBMARINE Prairial) were armed with a single 450 mm internal bow torpedo tube, but after an accident that lead to the sinking of FRENCH SUBMARINE Fresnel in 1909, the tubes were removed from Pluviôse and Messidor. A ministerial order of 18 March 1910 added one to FRENCH SUBMARINE Vendémiaire while she was still under construction, but the bow tubes were deleted from the rest of the class. 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; those with bow tubes carried their reload in the torpedo compartment.

Service
The Pluviôse class were acknowledged to be good sea boats and saw action throughout the First World War on patrol and close blockade duty. Of the eighteen built, five were lost. One (FRENCH SUBMARINE Vendémiaire) was accidentally lost prior to the war, in 1912. Two others, Floréal and FRENCH SUBMARINE Priarial, were lost accidentally during the conflict, while FRENCH SUBMARINE Monge and FRENCH SUBMARINE Fresnel were lost in action.