Australian Cruiser Tank Mk. IV "Lightning"

As the armoured forces of its enemies grew in capabilities, the AC3 Thunderbolt's impressive armament eventually encountered models of heavy and medium tanks it could not effectively fight. In response, a new turret was designed for the AC3 chassis; the resulting tank would become the AC4 Lightning. Armed with a 17-pounder gun in a much wider turret ring, while retaining the armoured protection and speed of its predecessor, the AC4 Lightning became the most capable tank in the republican armed forces. When loaded with experimental Tungsten APDS shot, the AC4 could penetrate any heavy tank in the world save for some super-heavy prototypes. Mass production began in 1944.