 Two HS-1Ls operating from Chatham, Massachusetts made the only confirmed aircraft attack on a German U-boat in American waters on July 21, 1918, but this was unsuccessful, with bombs failing to explode and the submarine escaping.From August 1918, in order to compensate for Canada's lack of patrol aircraft, US Navy HSs operated from two bases in Nova Scotia.Twelve HS-2Ls were donated to Canada at the end of the war.