American 3-inch Gun Motor Carriage T24/T40/M9

3-inch Gun Motor Carriage T40 prototype. This 3-inch self-propelled gun was the rebuilt T24 by Baldwin Locomotive in 1941. The Japanese attack caused this model to be accepted for production, however, the project was terminated in April 1942. The Tank Destroyer Board felt that the vehicle was too slow and the M1918 gun was not available in quantity.

T24 Gun Motor Carriage

The U.S. Army expressed a need for a vehicle capable of stopping and destroying enemy tanks. The new vehicle, dubbed the "Tank Destroyer", would have the same armor protection and general mobility of a standard tank, but would be heavily armed with enough punch to decimate enemy armored formations. Up until 1941, the only vehicles available were modified trucks and half-tracks, which lacked greatly in the mobility, firepower and armor departments.

During the summer of 1941, Baldwin Locomotive Works began development of a vehicle to fill the need for a true tank destroyer. They began with the chassis of an M3 Lee medium tank, added a modified superstructure with an open, hexagonally-shaped top, and armed the vehicle with the M1918 3-inch gun. The Ordnance Department accepted the vehicle for testing at Aberdeen at the end of the summer, designating it the T24 gun motor carriage. However, the extremely high silhouette of the vehicle was thought to detract from its ability to stalk its prey, and gun was found to be lacking in range and accuracy. The T24 was returned to Baldwin for adjustments.

T40/M9 America's First Tank Destroyer

What Baldwin later returned to the Army was basically a somewhat improved T24. Indeed, it was the T24 pilot vehicle, simply modified with a slightly lower superstructure and some minor improvements to the weapon and related systems. The vehicle was accepted for testing at Aberdeen once more, this time under the designation of T40. The Ordnance Department was still far from impressed, but a surprise attack on Pearl Harbor by the Japanese, and the subsequent entry of the United States into the war prompted the vehicle's adoption as the Army's first standardized full-track tank destroyer. It was christened the 3-inch Gun Motor Carriage M9 and a production contract was awarded for 1,000 examples.

However, as the vehicle was not truly up the Army's standards, the contract was cancelled only four months later, in April 1942. The M9 had simply proven too slow, and furthermore, its 3-inch main armament was not available in sufficient quantity. As the vehicle had a basis on the M3 Lee medium tank, the silhouette was also above the minimum for a vehicle intended as an ambush predator. The Tank Destroyer Board finally abandoned the project at the end of the summer of 1942, officially due to the insufficient mobility and speed of the vehicle.

Experimental 3-inch Gun Motor Carriage T24. This 3-inch self-propelled gun was built by Baldwin Locomotive in 1941 and was intended as an anti-tank weapon. Tests showed that it was too tall and was sent back to Baldwin for adjustments.

3-inch Gun Motor Carriage T40 prototype.

3-inch Gun Motor Carriage T40 prototype. 

3-inch Gun Motor Carriage T40 prototype.