 The M4, M4A1, early production M4A2 and early production M4A3 possessed protruding cast "hatchway" structures that allowed the driver and assistant driver's hatches to fit in front of the turret ring.In these areas, the effect of the glacis plate's slope was greatly reduced.Later Shermans had an upgraded glacis plate that was uniformly thick and sloped at 47 degrees from the vertical, providing an effective thickness of over the entire plate.