HMS K2 was the second of the K class submarines and was built at HM Dockyard, Portsmouth, England. She was laid down on 13 November 1915 and was commissioned in May 1917 one year before the end of World War I. K2 had an unsuccessful start. In January 1917, she was damaged by an explosion and fire during her first diving trials. On 11 January 1924, K2 collided with K12 as they departed from Portland Harbour. K2 smashed a hole in the forward casing of K12 and buckled her bows for about . This collision yet again showed the perils of exercising with heavy units.