The M40 Gun Motor Carriage (GMC) was developed to replace the successful M12 155mm GMC built of the older M3 Chassis with the new vehicle built on the M4A3 chassis using the new HVSS suspension, this configuration first seeing service as the M4A3E8. The M40 was armed with the newer 155mm M1 gun with the engine moved midships and the large open rear area used to mount the M1 gun.

The M40 was first used in the closing months of WWII but was most notably used as the mainstay of US Artillery during the Korean War.

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