M3 (Lee I/Grant I).
Riveted hull, high profile turret, gasoline engine. 4,724 built.
M3A1 (Lee II).
Cast (rounded) upper hull. 300 built.
M3A2 (Lee III).
Welded (sharp edged) hull. Only 12 vehicles produced.
M3A3 (Lee IV/Lee V).
Twin GM 6-71 diesel variant of welded hull. Side doors welded shut or eliminated. 322 built.
M3A4 (Lee VI).
Stretched riveted hull, 1 x Chrysler A-57 Multibank engine, made up of 5 4.12 litre 6-cyl L-head car engines (block upwards) mated to a common crankshaft, displacement 21 litres, 470 hp @ 2700rpm. Side doors eliminated. 109 built.
M3A5 (Grant II) .
Twin GM 6-71 diesel variant of riveted hull M3. Despite having the original Lee turret and not the Grant one, was referred by the British as Grant II. 591 built.
The United States also developed medium tanks, the need for which was clearly revealed in the 1940 Battle for France. Although U.S. observers during the Spanish Civil War had reported that a low silhouette, a 360-degree traverse turret, and a powerful engine were more important features than armor protection, the earliest U.S. medium tanks hardly met these criteria. The M2 medium tank with its 37mm gun entered limited production in August 1939. An improved model, the M2A1, was introduced the next year. Weighing some 47,000 pounds, it differed chiefly from the original in having a wider turret, increased maximum armor thickness of 32mm (from 25mm), wider tracks, and a supercharger that delivered 400 hp.
Mass production of the new tank was already under way by American Car & Foundry, and a contract had been signed to produce 1,000 of them at a new Chrysler factory to be built in Michigan (known as the Detroit Tank Arsenal) when the M2 was rendered obsolete by the demonstrated superiority of the heavier-gunned (75mm) German PzKpfw IV in the Battle for France. In August the commander of the Armored Force, Brigadier General Chaffee, met with Ordnance Department representatives at Aberdeen Proving Ground, Maryland, where a consensus emerged in favor of a 75mm gun for the army’s medium tanks. As there was insufficient room in the M2’s small turret for such a large main gun, the army decided in favor of developing an interim AFV that would incorporate the hull, general layout, and mechanical arrangements of the M2 yet mount a limited-traverse 75mm gun on the right side of the hull sponson. At the same time, work would proceed on a new medium tank with a 75mm gun in a turret capable of full traverse. In August the government contract with Chrysler for the M2A1 was canceled and rolled over to the new as-yet undesigned AFV, designated the M3. Only 94 M2s were actually built, and they were used only for training purposes.
The M3 was designed, tested, and rushed into mass production probably faster than any other tank in history. Critical in the large numbers produced was construction of the Detroit Tank Arsenal at Center Line, Michigan, conceived to mass-produce the M2. Following the defeat of France, the United States adopted a new national munitions program that included large numbers of medium tanks. William S. Knudson, president of General Motors and a member of the National Defense Advisory Commission responsible for coordinating U.S. industry with national defense requirements, believed that heavy engineering firms would not be capable of turning out the large volume of tanks required and that this could be met only by the automobile manufacturers. Knudson suggested that a new tank-manufacturing facility be built to employ the mass-production assembly lines used in the automobile industry and arranged for Chrysler to build and operate the plant for the U.S. government. Work commenced on the huge new Detroit Tank Arsenal (1,380 feet by 500 feet) in September 1940 and was completed in only six months.
At the same time, Rock Island Arsenal was working with Chrysler engineers to design the M3. Rock Island consulted with the firms that would build the new tank, as well as with members of the British Tank Commission who had been sent to the United States in June 1940 to acquire U.S.-built tanks for the British Army. The British provided useful input based on actual combat experience against the Germans in the fighting for France.
Beginning in April 1941 three firms produced M3 pilot models, and by August full production was under way at American Locomotive, Baldwin, and Detroit Arsenal. Outclassed when it was built, the M3 was conceived as an interim design. Nonetheless, a total of 6,258 M3s were produced through December 1942 in a half-dozen different models.
The 30-ton Medium Tank M3 was similar in dimensions to the M2A1 it replaced and had the same engine and suspension system. The M3 had a 10-foot, 3-inch silhouette and was powered by a Wright radial 340-hp engine that produced a maximum speed of 26 mph. It had a crew of six, maximum 37mm armor, and mounted a 75mm gun in the right sponson with secondary armament of a turreted 37mm gun and three or four .30-caliber machine guns. The 75mm gun had only a 34-degree traverse, but the 37mm gun in the left-offset turret had full 360-degree traverse. The turret and sponson were cast, but the hull initially was of riveted armor. The M3 also had side doors in the hull.