I21 or I-21 may refer to: * Japanese submarine I-21, an Imperial Japanese Navy submarine completed in 1941 and sunk in 1943 * Japanese submarine I-121, named I-21 from 1924 to 1938, an Imperial Japanese Navy submarine completed in 1927 and scuttled in 1946, * (1816–1892), a Swedish infantry regiment, split from the Närke-Värmland Regiment * Kalmar Regiment (1893–1927), a Swedish infantry regiment * Västernorrland Regiment (1928–1974), a Swedish infantry regiment This disambiguation page lists articles associated with the same title formed as a letter-number combination. If an internal link led you here, you may wish to change the link to point directly to the intended article.