The Diane class consisted of a pair of submarines built for the French Navy during World War I. Completed in 1916âÂÂ1917 the boats played a limited role in the war. sank with the loss of all hands in 1918, but her sister survived the war. She was sold for scrap in 1936.
The Diane class was built as part of the French Navy's 1912 building program; Naval constructor Jean Simonot was unhappy that his double-hull design for the submarine had been modified to use steam engines rather than the diesel engines that he had specified and proposed a version of his design scaled down by a factor of 0.92, using the same smaller diesels as the submarine . The boats displaced surfaced and submerged. They had an overall length of , a beam of , and a draft of . Their crew numbered 34 officers and crewmen.
For surface running, the Diane-class boats were powered by two diesel engines, each driving one propeller shaft. The Sulzer two-cycle engines in Daphné were designed to produce a total of , but proved to be unreliable at that rating and output was restricted to . This reduced the boat's speed from the designed to . The engines for Diane had been ordered from Chaléassière in 1913, but the company proved unable to deliver them in a timely manner and a pair of Vickers eight-cylinder, four-cycle engines had to be purchased from Britain in 1915. When submerged each shaft was driven by a electric motor. The designed speed underwater was , but the boats only reached during their sea trials. The Dianes had a maximum fuel capacity of which gave them a surface endurance of at . Their designed submerged endurance was at , but sea trials showed that it fell short of that figure at .
The Diane class was armed with a total of ten torpedoes. Four of these were positioned in the bow; two in internal torpedo tubes in the bow angled outwards three and a half degrees and two in external tubes above them angled outwards nine degrees. Four more were located in four external rotating launchers amidships, two on each broadside; one pair each fore and aft of the conning tower that could traverse 130 degrees to the side of the boats. The last pair were in external tubes in the stern aimed directly aft. While the boats were under construction in 1915 a Mle 1897 gun with high-angle capacity was ordered to be installed aft of the conning tower. Daphné is known to have received one, but it is uncertain if Diane did.