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.
The M3 underwent a half-dozen modifications, the most important of which was the introduction of gyro-stabilizers on both heavy guns, permitting accurate fire while under way. Both guns were fitted with periscope sights, and the turret could be traversed by power or by hand. The British used the standard M3 version in North Africa, naming it the “Lee” for U.S. Civil War Confederate General Robert E. Lee. Beginning with the M3A3, the “rivet popping” during battle that plagued the Lee in fighting in North Africa was eliminated with the introduction of an all-welded hull. At the same time, the side doors were either welded up or eliminated.
The British placed special orders for M3s from U.S. manufacturers under the “Cash and Carry” arrangement, a U.S. program whereby the United States would sell war materials to belligerents provided they could pay cash for the purchase and transport the materials in their own vessels. The M3s had slightly longer cast turrets, did away with the cupola, and had other modifications. These M3s saw extensive service in North Africa. The British knew this version of the M3 as the Grant after U.S. Grant, the Union general of the U.S. Civil War and 18th president of the United States. Some 200 of these Grants arrived in the Middle East early in 1942, and for the first time in the war the British had a tank superior in firepower to any Axis tank. They gave the British a quantitative as well as qualitative edge. The M3’s main gun could outrange the German tanks and fire AP shells against enemy tanks and HE shells in an infantry close-support role. A total of 167 Grants constituted the bulk of AFVs in the British 4th Armored Brigade in the important Battle of Gazala beginning in late May 1942. Two authorities have described the M3 as “at that time, the most important new addition to the British armoury.”
The passage by Congress of Lend-Lease legislation in March 1941 made U.S. weapons and war supplies of all kinds available on a lease/loan basis to countries fighting the Axis powers. This allowed the British to obtain the standard M3 version for service in North Africa. By June an additional 250 M3 tanks had arrived for Eighth Army in Egypt, and by the time of the Battle of El Alamein at the end of October, a total of 600 M3s had been delivered under both “Cash and Carry” and Lend-Lease. By June 1942 U.S. personnel were stationed at a maintenance facility near Cairo to assist the training of their British counterparts in the M3 and then the M4. Although most M3s were shipped to the Middle East, some were also sent to Britain for training and special conversions. When M4s began to replace M3s in North Africa, the remaining M3s were sent on to Burma to replace obsolete Matildas, Stuarts, and Valentines. The M3 appeared in a variety of variants, and its chassis was used in the development of gun motor carriages, including the M12, which mounted a 155mm gun. The U.S. Army employed it as a heavy bombardment weapon in European fighting in late 1944 and early 1945, including the taking of Köln (Cologne).
In October 1941, when the M4 Sherman became the U.S. standard medium tank, the army reclassified the M3 as “substitute standard.” In April 1943, when the M4 came into full service, the M3 became “limited standard,” and in April 1944 it was declared obsolete.
Even while design work was being carried out on the M3 tank, the Armored Force Board drew up specifications for its successor. These called for a 75mm gun, but unlike the M3, the new medium would carry the heavier gun in a full-traverse turret. In April 1941 the Armored Force Board decided to employ the straightforward approach of utilizing the M3 medium chassis, power plant, transmission, suspension, and other parts where possible while introducing a new cast or welded hull top and new central turret. A pilot model, designated T6 and employing the same hull side doors as the M3, underwent testing at Aberdeen Proving Ground in September 1941. The next month the T6 was redesignated Medium Tank M4.
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