The Sisu, built in 1939 at Wärtsilä Hietalahti Shipyard in Helsinki, was a pioneering Finnish icebreaker renowned for its diesel-electric propulsion system, making it one of the first of its kind in the world. Measuring approximately 65.3 meters in length with a beam of 14.4 meters, she displaced about 2,075 tonnes when loaded to her normal draught of 5.1 meters. Her hull featured a rounded midship design, with a 23-degree stem angle, and was divided into eight watertight compartments protected by a continuous double bottom. The hull was reinforced with a 25 mm thick shell plating for icebreaking, supported by transverse frames spaced every 400–450 mm. Sisu's powertrain comprised three Atlas Polar eight-cylinder diesel engines, each producing 1,600 hp, directly coupled to Strömberg generators. These supplied electricity to three DC motors—two for the stern propellers and one for a forward-facing propeller—via a Ward Leonard drive system, providing she with significant maneuverability and icebreaking capability. Her propulsion system delivered a total power output of around 4,005 hp, allowing her to operate efficiently in icy conditions. Designed for a crew of 51 during winter operations, Sisu could accommodate over 100 personnel in the summer when serving as a submarine tender. Her equipment included a towing winch and a bow notch for escorting ships. The vessel's internal layout consisted of engine rooms amidships, with tanks for fuel, lubricants, water, and ballast. Throughout her service, Sisu played a dual role: as a dedicated icebreaker ensuring navigation through the Baltic's winter ice, and as a submarine tender for the Finnish Navy during summer months. She participated in wartime operations during the Winter War and Continuation War, operating in the Gulf of Finland and the Baltic Sea, and was damaged in 1943 after striking a Soviet mine. After her decommissioning in 1975, she was renamed Louhi and served mainly as a depot ship until her final decommissioning in 1986, when she was scrapped. Her technological innovations and versatile service record highlight her significance in Finnish maritime history.

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