 The turret front armor was 76.2 mm thick, angled at 30 degrees from the vertical, giving an effective thickness of .The opening in the front of the M4's turret for the main gun was covered by a rounded thick rotor shield.Early Shermans that had a periscopic sight for the main gun mounted in the turret roof possessed a small thick mantlet that only covered the hole where the main gun barrel protruded; the exposed barrel of the coaxial machine gun was vulnerable to bullet splash or shrapnel and a small armored cover was manufactured to protect it.