Raeder's intention to fight a commerce war against Britain was the basis for Plan Z,[1] which included twelve ships of the P-class design.[2] The design work on the new ships proceeded in parallel with work on the O-class battlecruiser design.[5] Experiments were conducted on at least nine different design proposals between March 1938 and December 1939. The designs varied somewhat in terms of dimensions as well as armament; some of the designs featured three 28 cm triple turrets.[3]