The T21 light armored car was a Studabaker design produced to the same specifications that produced the Ford M8 light armored car, but only one pilot vehicle was constructed before the project was cancelled.
In July 1941 the US Army began work on a new design for a vehicle that could serve as a light tank destroyer and an armoured car. These vehicles were to carry a 37mm Gun M6 and a bow machine gun. They were to be adaptable for other purposing, including as a mortar carrier, multiple gun carriage or cargo carrier. In March 1942 the bow machine gun was replaced with a coaxial gun to be carried in the turret. On 22 October 1941 it was decided to order two six wheeled pilot vehicles, one from Ford (the T22) and one from Fargo (the T23).
On 10 December 1941 the Ordnance Committee recommended ordering four pilot vehicles instead, two from Ford and two from Fargo. The extra vehicles would be four wheeled vehicles – the Ford T22E1 and Fargo T23E1. Soon after this, presumably because they were aware of the potential for very large orders for the winning design, Studebaker offered to build a similar armoured car at their own expense. This vehicle would have all of the same military capabilities as the Ford and Fargo designs, but with independent suspension. On 29 January 1942 the military accepted this offer, and designated the Studebaker vehicle as the 37mm Gun Motor Carriage T43. On 12 March the designation was changed to the Light Armored Car T21.
Studebaker produced a six wheeled vehicle, with a large gap between the first and second pairs of wheels. Large sponsons filled the gaps between the wheels. As with the Forge and Fargo designs the engine was mounted at the rear. On the T21 the engine cover was split into two (left and right), with hinges at the narrow front end. Ventilation ports were built into the top of the engine covers. The T21 was powered by a Hercules JXD six-cylinder inline engine which provided 112hp to the five speed manual transmission. Only the rear four wheels were powered.
The 37mm gun was carried in an open topped turret, made from cast steel. The turret had sloped sides and a largely circular plan with a flat front to hold the gun. The driver’s compartment was in front of the turret, and had armoured shields to the front and sides, each with direct vision ports for use when the vehicle was closed up for action. Frustratingly none of the pictures of the T21 show the roof of the driver’s compartment when the shields are raised, but it must have had an armoured roof. Both the Ford and Fargo vehicles had a large sloped glacis at the front of the vehicle. In contrast the T21 had a stepped nose, with a gently sloping top section leading to a smaller ‘V’ shaped nose.
The prototype of the T21 was delivered to the General Motors Proving Ground for government tests on 22 May 1942. By this point the T22 had already been accepted for standardization as the Light Armored Car M8, so the chances of the T21 being ordered into production were already slim. These disappeared during the tests. The gap between second and third gears was found to be too large, reducing the vehicle’s responsiveness at low speeds, while the gap between fourth and fifth was too small, reducing the usefulness of fifth gear. There were also some clutch failures, which were blamed on over-speeding, suggesting that the clutch wasn’t robust enough for combat operations. The driver’s compartment was unsuited for a tall driver.
The T21 then went to the Special Armored Vehicle Board for further tests in October-November 1942, after which the board recommended ended the development of the T21. The project was officially cancelled on 21 January 1943.