The first series; the M1935 were ordered in the late 1930s to replace worn out World War I vintage boats. These ships proved versatile and seaworthy. The vessels could also undertake convoy escort, anti-submarine warfare and minelaying tasks as well as minesweeping. However, the ships were very expensive and complicated to build, and their oil-fired boilers meant they suffered from the fuel shortages in the later years of the war. A total of 69 ships were built in eight different shipyards, between 1937 and 1941. 34 were lost during the war. The general purpose boat of the war for the Kriegsmarine, the M35 was produced with many variants. Some had torpedoes, some were specialized as submarine hunters, some specialized as minesweeper, minelayers. Designer Quibquib