most German anti-tank weapons. The thickness of the M10's armor ranged from . The lower hull, being modified from that of a standard M4A2 or M4A3 Sherman tank, had armor on the sides and rear, and a floor. The rounded, cast transmission cover was thick. In a departure from its M4 Sherman parent, the M10 lacked the extra -inch floor plate under the driver's and assistant driver's stations that provided them additional protection from mines. The glacis plate was thick, sloped at 55 degrees from the vertical. The sides and rear of the upper hull were thick, sloped at 38 degrees from the vertical. The rear upper hull plate was used for storage of the vehicle's pioneer and maintenance tools: a axe, a crowbar, a mattock handle and head, a double-sided sledgehammer, and a track tensioning wrench. The sides and rear of the upper hull featured angled extensions or covers over the upper run of track. These extensions often got in the way of fitting "duckbill" extended end connectors, used to reduce ground pressure on soft ground, and were often removed, along with the front fenders, by maintenance units. The hull roof plate ranged from thick over the driver's and assistant driver's stations and turret ring, to thick over the engine compartment. The manually rotated turret of the M10 was a pentagonal shape. The sides were sloped 15 degrees inward from the vertical and were thick. The rear of the turret was also 1 inch thick. The partial roof on the front third of the turret opening was thick. The triangular cast gun shield sported the thickest armor on the vehicle, . It was sloped at 45 degrees from the vertical and horizontal. The M10 and M10A1 were mechanically identical except for their power plants. The M10 used the General Motors 6046, a twin engine formed from two Detroit Diesel 6-71 inline engines mated to a single output. The tandem engine produced at 2,100 rpm. One advantage of the GM 6046 was that the engines could be disconnected at will from the output and run independently. If one of the engines was damaged or destroyed, it could be disconnected and the other engine used to move the vehicle. The engine of the M10A1 was the Ford GAA, an 8-cylinder derivative of an ill-fated V-12 aircraft engine project. It produced at 2,600 rpm. When tested side by side in September 1943,