In the early days of the war the desirability of reducing the weight of areoplane engines to a minimum, consistent with reliability and efficiency, very soon led designers to consider the advisability of using alloys considerably lighter than cast iron or steel for all possible parts of aero engines. Aluminium alloy crank cases had been used for some years in connection with motor car engines, and it was natural, therefore, that such alloys should come into use for the crank cases of aeroplane engines.