125mm Smoothbore Cannon Co-Axial .50 Cal Machine Gun Optional Pintle mounted .50 Cal Machine Gun, 20mm Autocannon or GPMG
Or
165mm AT Gun Optional Pintle mounted .50 Cal Machine Gun or 20mm Autocannon
Adopted after tankers complained that the large size of the Mk.2 (P.400) gun made reloading time consuming and not fit for a main battle tank. Other improvements include thicker, more sloped armour, a larger space for crew and a drive system that doesn't force crewman to remove two wheels to get to one inner damaged wheel.
An anti tank variant was also adopted that has proved just as effective against highly reinforced bastions. It uses a deadly 165mm cannon that can destroy most armoured vehicles from extremely long ranges. The extreme length of the gun is no downside as the gun can collapse onto itself and move back into the turret slightly, shortening the length of the vehicle considerably. The gun can then be extended again quickly for combat.