In April 1943 the US Ordnance Department and Cadillac begin work on a new light tank with a 75 mm gun to replace the M5 Light Tank. Two pilot models (T24) were delivered in October 1943 by the Cadillac Motor Division. The Ordnance Department immediately ordered 1,000 before service tests had begun and then raised to 5,000 vehicles. First delivered in late 1944. American Car & Foundry and Massey-Harris also produced the M24. It was named after US Army tank pioneer General Adna R. Chaffee