As completed, the M4 Sherman origins of the M40 could clearly be identified, particularly at the sloping glacis plate at front. Running gear included six road wheels to a hull side with the drive sprocket at front and track idler at rear. The crew numbered eight and included the driver, commander, and up to six of the gunnery crew. All told, the vehicle weighed some 40 tons with 12mm of armor protection and its 155mm main gun barrel. Dimensions included a length of 29 feet, 10 inches, a width of 10 feet, 4 inches and a height of 8 feet, 10 inches. Power was served through a Continental R975 EC2 gasoline engine of 340 horsepower. This provided the vehicle with a maximum road speed of 24 miles per hour and a range of 105 miles. Suspension was through the same Horizontal Volute Spring Suspension (HVSS) arrangement seen in the Sherman M4A3 model.
The 155mm main gun fired a 95lb explosive shell out to 25,175 yards. It sat atop a complex recoil mechanism and structure that allowed for the necessary elevation. Onboard storage allowed for twenty of the massive 155mm shells to be carried so the M4A1 tractor served to tow an M23 ammunition trailer.
The T89 Howitzer Motor Carriage (detailed elsewhere on this site) was a related M40 development though mounting an even more powerful 203mm howitzer system. The vehicle was standardized in November of 1945 - missing out on action in World War 2 - and was designated as the M43 Howitzer Motor Carriage in service. These chassis was convertible back to M40 forms if needed.
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