At the outbreak of World War One, the navy consisted of two cruisers purchased from the Royal Navy and two submarines purchased from the United States in August 1914. These four vessels were the only offensive warships to serve in the RCN during the war.

The Naval Service Act provided however, that ships belonging to government departments such as Fisheries and Hydrographic Services, could be incorporated as naval vessels in time of war, and together with the purchase of five former yachts, a host of tugs and motor launches, this motley collection of vessels did a thorough job as patrol craft and minesweepers during the four years of the First World War.