Germany began developing its heavy armored cars well before the outbreak of WWII. Germany's early six-wheel armored cars were based on 6x4 truck chassis, and their off-road mobility was limited. These vehicles soon gave way to an expanding series of eight-wheel-drive eight-wheel-steer vehicles fitted with a variety of armament. In time, these too were supplanted by even larger armored cars incorporating refinements based on lessons learned from the vehicles' field experience, such as heavier armor, armament, and an air-cooled engine.