In May of 1941, Marmon-Herrington Company Inc. received an order for an airborne tank. In August, a full sized model of the newly indexed Light Tank T9 was ready. Further development of this project resulted in the M22 airborne tank, referred to as "Locust" by the British. This was the only airborned tank used for its intended purpose in WWII.
Light, low, and fairly long, the Light Tank T9 interested the military as a chassis for a tank destroyer. Unlike the Light Tank T3 chassis, the goal here was not to include a large caliber. The year was 1941, and the 37 mm gun was sufficient to fight most enemy tanks. The American military did not know about the Soviet T-34 and KV-1 or that the Germans were hard at work on tanks with thick, anti-shell armour.
In the fall of 1941, the 37 mm Gun Motor Carriage T42 project was launched. The draft project was ready by October 27th. The initial concept of the vehicle differed little from the Light Tank T9. The biggest difference was in the roomier turret with an open to. This turret contained the same 37 mm M5 gun and a Browning M1919 machinegun. Another machinegun was installed in the hull.
This concept did not stick around for long. Calculations showed that this design would not work. The new turret would need a longer hull, and the suspension had to be lengthened to make the vehicle more stable. On November 7th, 1941, a document was prepared listing improvements in the T42's design. The hull and tracks were to be lengthened by 30 cm and the clearance increased from 28 cm to 35.5 cm. The suspension would also be redesigned.