M3A1. M5A1 (Stuart VI) 6,810 produced. M5 with the turret of the M3A3; this was the major variant in US units by 1943. 75mm Howitzer Motor Carriage M8 1,778 units produced between September 1942 and January 1944. Based on M5 chassis. The gun was replaced with the 75 mm M2/M3 howitzer in open turret and a trailer hook was fitted so an ammunition trailer could be towed. Provided fire support to cavalry reconnaissance squadrons. T6 Armored Recovery Vehicle Armoured recovery vehicle based on the chassis of an M5A1. Project was discontinued in 1943 in favor of the M24 Chaffee-based T6E1. T16 4.5-inch Gun Motor Carriage Self-propelled 4.5-inch gun based on the chassis of an M5. Project was discontinued in 1943. T18 Howitzer Motor Carriage Self-propelled gun based on M3 chassis. 75 mm M1A1 pack howitzer was mounted in a boxy superstructure. The project started in September 1941 and was abandoned in April 1942. Only two were produced, 75 mm Howitzer Motor Carriage M8 was chosen to be produced instead. T27 / T27E1 Mortar Motor Carriage M5A1 with turret replaced by superstructure in which an 81 mm mortar was installed. Also carried .50 (12.7 mm) cal Browning M2HB machine gun. The project was abandoned in April 1944 because of inadequate crew and storage space. T29 Mortar Motor Carriage Design similar to T27, with 4.2 inch (107 mm) mortar. Was abandoned for the same reason. T56 Gun Motor Carriage Self-propelled gun based on M3A3 chassis. The engine was moved to the middle of the hull and a 3-inch (76 mm) gun was mounted in a superstructure in the rear. The project started in September 1942 and was abandoned in February 1943. T57 Gun Motor Carriage Variant of T56 with Continental engine of the Medium Tank M3. Also dropped in February 1943. T81 Chemical Mortar Motor Carriage M5A1-based 4.2 inch (107 mm) chemical mortar carrier. T82 Howitzer Motor Carriage Self-propelled 105 mm howitzer based on M5A1 chassis. Development began in 1943. Two prototypes built and tested in August 1944 at Aberdeen Proving Grounds. Project was discontinued on June 21, 1945. M3 with Maxson Turret Anti-aircraft variant developed in 1942. Was armed with four .50 (12.7 mm) cal. machine guns in a turret developed by Maxson Corp. The project was rejected because of the availability of the M16 MGMC. 155 mm Howitzer Motor Carriage T64 Self-propelled howitzer based on lengthened M5 with 155 mm