Complex sentence: The Firefly's secondary armament was the standard.30 inch (7.62 mm) coaxial machine gun in the turret; the hull-mounted machine gun was removed to increase ammunition storage for the main gun.
Split into simpler sentences: The Firefly's secondary armament was the standard.30 inch (7.62 mm) coaxial machine gun in the turret. The hull-mounted machine gun had been removed to increase ammunition storage for the main gun.