Five classes of submarine are known as the S class:

• The British S-class submarine (1914) of three boats built by Scotts of Greenock in 1914–1915 and transferred to the Italian Regia Marina in 1915.
• The Italian S-class submarine of the Italian Regia Marina consisted of three boats built by Laurenti-Fiat between 1914 and 1919. Length: 148 feet Surface Tonnage: 265 Crew: 28. All were withdrawn from service prior to World War II.
• The United States S-class submarine of the United States Navy of 51 boats built between 1918 and 1925.
• The British S-class submarine (1931) of the British Royal Navy of 62 boats built in the 1930s and 1940s.
• The Soviet S-class submarine of World War II vintage.
• The Ha-9-class submarine also called Type S of the Imperial Japanese Navy of 2 boats built between 1917 and 1920.