The M3 hull was used as the basis for a tank destroyer mounting the 3-inch gun, a reworked World War-era weapon - by removing the turret, sponson gun and hull roof. It was developed in September 1941 but in tests the resulting vehicle was judged to be too tall and the gun mount was not suitable for mass production so the T24 project was cancelled in 1942;

The T40 was the T24 prototype rebuilt by Baldwin Locomotive Works in 1942. The gun mounting was lower than the T24.
The design was standardized with designation M9 GMC with a "limited standard" production of fifty vehicles in April 1942.
Only 28 guns were available and the M9s were not expected to be complete by the time the superior M10 tank destroyer design was in production, so the M9 was cancelled in August 1942.