HMCS Grilse was a commissioned patrol boat of the Royal Canadian Navy during the First World War. Launched in 1912 as the private yacht Winchester of the American industrialist Peter Rouss, the vessel was constructed along the lines of a contemporary Royal Navy torpedo boat destroyer. After the outbreak of war, vessels that could be used by belligerents was prohibited by the government of the then-neutral United States. Canadian millionaire J. K. L. Ross purchased Winchester and returned to Canada with the yacht, where he transferred ownership of the vessel to the Royal Canadian Navy. Renamed Grilse, a pseudonym for Atlantic salmon and converted to a patrol boat, the vessel was deployed as part of Canada's east coast patrol combating the German submarine threat. After the war, she was sold