The German employment of armor divisions in the September 1939 German invasion of Poland, and especially in the May–June 1940 defeat of France, dramatically changed U.S. Army attitudes toward tanks and their role. In April 1940 an improvised U.S. armored division, formed from the 7th Cavalry Brigade (Mechanized) from Fort Knox, Kentucky, and the Provisional Tank Brigade from Fort Benning, Georgia, dominated the army’s Louisiana maneuvers. Then, in July 1940 the army created the U.S. Armored Force, led by Brigadier General Adna Romanaza Chaffee Jr., to test the feasibility of tank divisions. In July 1943 the Armored Force was redesignated the Armored Command, and in February 1944 it became the Armored Center, ending the hopes of some that the Armored Force would become a new branch of the army.
The first U.S. light tank introduced after the start of the war in Europe was the M3 series of light tanks. Based on the M2A3, the M3 was designed at Rock Island Arsenal in the spring of 1940 and incorporated lessons learned in the early European fighting. Approved in July 1940, the M3 entered production in March 1941. The M3 saw extensive service in North Africa with the British (who called it the General Stuart) and then the Americans.
The M3 went through three different models, eventually incorporating a gyro-stabilizer for the main gun, a diesel engine, and an allwelded turret and hull (the first being riveted). It also received two jettisonable 25-gallon fuel tanks to increase its range in the desert. The problem with its riveted armor was that even a glancing shot to the hull by an enemy shell could sheer the heads off rivets and send the remainder flying around the inside of the tank, causing serious personnel injuries and/or igniting ammunition or damaging the engine.
The M3 weighed some 27,400 pounds, had a crew of four, maximum 51mm armor, and was armed with a 37mm gun in the turret and 3 x .30-caliber machine guns. The M3A1 version of 1942 eliminated the turret cupola to reduce overall height and also did away with the two sponsoned machine guns, fired remotely by the driver. These had proved of limited use, and doing away with them reduced the tank’s weight and increased its internal storage.
The final version M3A3 entered production in early 1943. Weighing some 31,800 pounds, it had a new all-welded hull that was enlarged by extending the sponsons and increasing the driver’s compartment forward and upward. This extra room allowed for additional ammunition storage and fuel tanks.
Although the M3 in its various models performed well in its primary reconnaissance role, the tank was both undergunned and underpowered. The M3 proved a welcome addition to British armor assets in North Africa in 1941–1942, and its crews there thought highly enough of the reliable M3 to refer to it as “Honey.” The U.S. Army declared the M3 obsolete in July 1943; it remained in the service of other nations through the end of the war and beyond.
The follow-on to the M3 was the M5 series, also designated the General Stuart. The same basic design as the M3, it had twin Cadillac automobile engines as well as the commercial Cadillac hydromatic transmission used in automobiles. Officials of the Cadillac Division of General Motors Corporation suggested this change to the Ordnance Department, which converted a standard M3 in the fall of 1941. Subsequent tests proved satisfactory.
Originally to be the Light Tank M4, the new tank was designated the M5 to avoid confusion with the M4 medium Sherman tank then entering production. Recognizable by its stepped-up rear deck to accommodate its new power plant, the M5 had the same hull as its predecessor, save for a sloping glacis. The M5 had a crew of four, weighed some 33,000 pounds with maximum 67mm armor, and had armament of one 37mm gun and two .30-caliber machine guns.
Superior to the M3, the M5 was not produced in large numbers because of the appearance of its successor, the heavier M24. The U.S. Army declared the M5 to be “substitute standard” in July 1944. In British service both the M5 and M5A1 were known as the Stuart VI.
In May 1941, following consultation with the Armored Force and the Army Air Corps, the Ordnance Department called for the manufacture of an airborne tank of 8 tons, about half the weight of an M5, with carriage dimensions so that it would be transportable either inside or under the belly of a cargo aircraft. Christie, General Motors, and Marmon-Herrington all submitted designs. The Marmon-Herrington design was judged to be best, and the government ordered a test model, designated the T9. Following initial testing, Marmon-Herrington built two other pilot models.
The production model, the M22 Locust, had a rolled plate hull and a cast turret. Four hull brackets facilitated slinging the hull under an aircraft. It also featured an easily removable turret to facilitate air transport. The Locust could also be transported in the hold of a British Hamilcar glider. The M22 was of conventional, although compact, design, but its thin armor gave it limited tactical application. It had a battle weight of 16,400 pounds, a crew of three, a 162- hp engine, a maximum speed of 40 mph, maximum 25mm armor, and mounted a 37mm main gun and one .30-caliber machine gun.
The M22 was a specialized, limited production tank. The follow on U.S. tank to the M5 was the M24 Chaffee. Based in large part on observations of British experience in the Western Desert with the M3 series of light tanks, the U.S. Army determined that its light tanks should mount a 75mm gun. The M5 series could carry the larger 75mm, but only with sharply restricted interior storage space; this forced the design of a new tank.
In April 1943 the U.S. Army Ordnance Department and Cadillac, which had produced the successful M5, began work on a new design that was to make use of the best aspects of the M5, such as the twin Cadillac engines and hydromatic transmission, while incorporating changes based on combat experience. The new design incorporated angled hull surfaces for maximum crew protection, and road wheels on torsion arms provided a smoother ride.
The first of two pilot models, delivered in October 1943, proved so successful that the Ordnance Department immediately ordered production, first for 1,000 vehicles, and then 5,000. At first designated the T24, the new tank was delivered to U.S. units late in 1944, replacing the M5. It was designated the M24 in May 1944.
The all-welded, 40,500-pound M24 had a crew of five, two 110- hp engines that delivered a maximum speed of 35 mph, maximum 25mm armor protection, and mounted a 75mm gun and three machine guns: two .30-caliber (one coaxial with the main gun) and one .50-caliber for antiaircraft protection. This highly successful tank combined a rugged design with high speed, simplicity, reliability, and heavy armament for its size. The M24 was also employed by the British Army, and it continued in U.S. service well after the war. It appeared in a variety of guises, all of which had the same engine, power train, and suspension system. These included howitzer and mortar motor carriages. The M24 could also be easily fitted with a dozer blade when necessary.