Commissioned into the Royal Canadian Navy on 1 April 1921 at Halifax it took two months to make "CH-15" and her sister operational. By July 1921 both boats were functioning and exercised with the rest of the Canadian armed forces practicing harbour defence. While in service the submarine was used primarily for training anti-submarine warfare. After arguing that remaining at Halifax during the winter months would be detrimental to the vessels' status, "CH-15" and her sister, accompanied by , wintered at Bermuda. The two submarines returned to Halifax in April 1922. Following the election of Mackenzie King government, the Naval Service was required to cut expenditures. Upon their return it was found that the government had refused to pay for the upkeep of the submarines and they were paid off on 22 June 1922.