 The ships design process started in 1936; the ships were intended for long-range commerce raiding.They were an improvement over previous designs, which suffered from insufficient range to be effective commerce raiders.However, the requirements placed on the design—high maximum and cruising speeds, long range, heavy armament, and armor sufficient to withstand 15 cm shells, all on a displacement no more than 8,000 metric tons—were deemed impossible by the design staff.