The United States' S-class submarines, often simply called S-boats (sometimes "Sugar" boats, after the then contemporary Navy phonetic alphabet for "S"), were the first class of submarines built to a United States Navy design. The United States Navy commissioned 51 S-Class submarines from 1920 to 1925. The first S-boat, USS S-1 (SS-105), was commissioned in 1918 and the last numerically, USS S-51 (SS-162), in 1922. The last of the class actually commissioned was USS S-47 (SS-158) in 1925. The S class is subdivided into four groups of different designs: