HMCS St. Julien was a Battle-class naval trawler built for the Royal Canadian Navy during World War I. Launched on June 16, 1917, by Polson Iron Works in Toronto, the vessel was part of a fleet of twelve trawlers designed to counter the German U-boat threat in the western Atlantic. These ships were modeled after British North Sea trawlers, optimized for anti-submarine patrols and escort duties along Canada's east coast. The St. Julien displaced approximately 320 long tons (around 330 tonnes), measuring 130 feet (40 meters) in length overall, with a beam of 23 feet 5 inches (7.14 meters) and a draught of 13 feet 5 inches (4.09 meters). Powered by a steam-powered triple expansion engine driving a single shaft, the vessel generated 480 indicated horsepower, reaching a top speed of about 10 knots (19 km/h). Armament on the St. Julien included a single QF 12-pounder 12 cwt naval gun mounted forward, intended as the smallest effective weapon against surfaced U-boats, complemented by a small complement of depth charges for anti-submarine warfare. The ship was commissioned into active service on November 13, 1917, and was assigned to patrol and escort duties out of Sydney, Nova Scotia, during the 1918 shipping season. Its operational role was critical in safeguarding Atlantic shipping lanes during the war. Following the war, the St. Julien was decommissioned from military service in 1920 and transferred to the Department of Marine and Fisheries. It was converted into a lightship, designated Lightship No. 22, with a lighthouse beacon installed at the foremast head and a foghorn atop a lattice tower. The vessel served as a navigational aid until 1958. After its decommissioning as a lightship, it was sold and renamed Centennial, remaining in service until 1978. The HMCS St. Julien holds maritime significance as part of Canada's early anti-submarine efforts in WWI and later as a navigational aid vessel, exemplifying the versatile use of wartime ships in peacetime maritime operations.

This description has been generated using GPT-4.1-NANO based on the Vessel's wikidata information and then modified by ShipIndex.org staff.