Panzer III
The Panzer III was intended to fight other tanks; in the initial design stage a gun was specified. However, the infantry at the time were being equipped with the PaK 36, and it was thought that, in the interest of standardization, the tanks should carry the same armament. As a compromise, the turret ring was made large enough to accommodate a gun should a future upgrade be required. This single decision later assured the Panzer III a prolonged life in the German Army.