US Army infantry tank design started with the light tank, T1 during the 1920s, which developed into a series of experimental designs which did not enter production.
The T2 concept, starting five years later, incorporated several design lessons from the T1, but used a new suspension system copied from the British Vickers six-ton tank.
The first prototype was delivered in 1933.

The Defense Act of 1920 had defined tanks to be used in support of the infantry.
Through the 1920s a number of theorists outlined an independent role for the tank that required it to move at high speed into the rear areas, a modern version of the cavalry.
The British referred to these designs as "cruiser tanks", but similar high-speed designs were developed under a variety of names.
As the Defense Act limited tank development to the infantry, the United States Cavalry began tank development under the name "combat car".
In keeping with the high-speed role, the new T5 combat car introduced the new vertical volute spring suspension (VVSS) system, which proved clearly superior to the Vickers leaf spring system.

This led to a second prototype of the T2, the T2E1, in April 1934, adopting the VVSS from the T5.
The T2E1 was armed with one .30 cal (7.62 mm) and one .50 inch (12.7 mm) Browning machine gun mounted in a fixed turret; another .30 cal Browning was mounted on the hull front.
The T2E1 was selected for production in 1935 as the M2, which mounted only the M2 Browning in a small one-man turret, and the .30 cal in the hull.

After only 10 units were delivered, the Infantry Branch decided to switch to a twin turret configuration in the M2E2, with a .30-caliber (7.62 mm) machine gun in a second turret.
These early twin-turret tanks were given the nickname "Mae West" by the troops, after the popular busty movie star.
The twin-turret layout was inefficient, but was a common feature of 1930s light tanks derived from the Vickers, such as the Soviet T-26 and Polish 7TP.
Further refinements to the M2A2 produced the A3 model, which incorporated a modified suspension system that reduced the tank's ground pressure.
The weight increased to 10 tons.

Following the Spanish Civil War, most armies, including the U.S. Army, realized that they needed tanks armed with cannon and not merely with machine guns.
The Cavalry had already opted for a single, larger turret on its nearly identical M1 combat car.
In December 1938, OCM No.
14844 directed that a single M2A3 be removed from the assembly line and modified with heavier armor and weapons, to meet the standards of the U.S. Infantry.
This vehicle, after conversion, was re-designated as the M2A4.
It was equipped with an M5 37 mm main gun, 1 inch (25 mm) thick armor, and a seven-cylinder gasoline engine.
Other upgrades included improved suspension, improved transmission, and better engine cooling.
Production of the M2A4 began in May 1940 at the American Car and Foundry Company, and continued through March 1941; an additional ten M2A4s were assembled in April 1942, for a total production run of 375 M2A4 light tanks.
The US Army sent out press photos still showing the M2A4 being assembled in July 1941 after the assembly line had been changed over to the M3.
US Army infantry tank design started with the light tank, T1 during the 1920s, which developed into a series of experimental designs which did not enter production. The T2 concept, starting five years later, incorporated several design lessons from the T1, but used a new suspension system copied from the British Vickers six-ton tank. The first prototype was delivered in 1933.
The Defense Act of 1920 had defined tanks to be used in support of the infantry. Through the 1920s a number of theorists outlined an independent role for the tank that required it to move at high speed into the rear areas, a modern version of the cavalry. The British referred to these designs as "cruiser tanks", but similar high-speed designs were developed under a variety of names. As the Defense Act limited tank development to the infantry, the United States Cavalry began tank development under the name "combat car". In keeping with the high-speed role, the new T5 combat car introduced the new vertical volute spring suspension (VVSS) system, which proved clearly superior to the Vickers leaf spring system.
This led to a second prototype of the T2, the T2E1, in April 1934, adopting the VVSS from the T5. The T2E1 was armed with one .30 cal (7.62 mm) and one .50 inch (12.7 mm) Browning machine gun mounted in a fixed turret; another .30 cal Browning was mounted on the hull front. The T2E1 was selected for production in 1935 as the M2, which mounted only the M2 Browning in a small one-man turret, and the .30 cal in the hull.
After only 10 units were delivered, the Infantry Branch decided to switch to a twin turret configuration in the M2E2, with a .30-caliber (7.62 mm) machine gun in a second turret. These early twin-turret tanks were given the nickname "Mae West" by the troops, after the popular busty movie star. The twin-turret layout was inefficient, but was a common feature of 1930s light tanks derived from the Vickers, such as the Soviet T-26 and Polish 7TP. Further refinements to the M2A2 produced the A3 model, which incorporated a modified suspension system that reduced the tank's ground pressure. The weight increased to 10 tons.
Following the Spanish Civil War, most armies, including the U.S. Army, realized that they needed tanks armed with cannon and not merely with machine guns. The Cavalry had already opted for a single, larger turret on its nearly identical M1 combat car. In December 1938, OCM No. 14844 directed that a single M2A3 be removed from the assembly line and modified with heavier armor and weapons, to meet the standards of the U.S. Infantry. This vehicle, after conversion, was re-designated as the M2A4. It was equipped with an M5 37 mm main gun, 1 inch (25 mm) thick armor, and a seven-cylinder gasoline engine. Other upgrades included improved suspension, improved transmission, and better engine cooling. Production of the M2A4 began in May 1940 at the American Car and Foundry Company, and continued through March 1941; an additional ten M2A4s were assembled in April 1942, for a total production run of 375 M2A4 light tanks. The US Army sent out press photos still showing the M2A4 being assembled in July 1941 after the assembly line had been changed over to the M3.
M2 light tank