One trend seen in World War II was the usage of older, lighter tank chassis to mount larger weapons in fixed casemates, as self-propelled guns, tank destroyers or assault guns. For example, the Soviet T-34 could mount an 85 mm gun in the turret, but the same chassis could carry the much more effective 100 mm gun in a fixed casemate as the SU-100, the successor of the SU-85. Likewise, the obsolete German Panzer II light tank, too vulnerable for a direct fire role, was modified to take a powerful 75 mm PaK 40 gun in an open-topped, fixed casemate as the Marder II self-propelled artillery piece.