Events in Western Europe rapidly demonstrated that the M2 was obsolete, and it was never used overseas in combat; it was, however, used for training purposes throughout the war.

Some features of the M2 series, especially the suspension and powertrain, provided the basis for later, important U.S. tank designs including the M3 Lee, M4 Sherman and other armored fighting vehicles.

Initially designated the T5, the redesigned model (with a 350 hp R-975 radial engine) was re-designated as the M2 Medium Tank in June, 1939.

[4] After the first 18 units had been produced at Rock Island Arsenal and evaluated by the Army, the upgraded M2A1 specification was approved with a redesigned turret and a more powerful engine.

Many components were common or used a similar design, including the tracks and vertical volute spring suspension which, with slight modifications, were later used on the M3 and M4 medium tanks.

[8] This armament configuration was an intermediate between the sponson-mounted weapons of the Mark VIII Liberty tank of World War I vintage, and the combination of turreted cannon, coaxial machine gun and glacis-mounted machine gun that was almost universal in World War II medium tanks.

[4][11] Events in Europe made it obvious that the M2 was obsolete, and the government modified the contract two weeks later, before production began.

The U.S. Army fielded the M2 and M2A1 with the 67th Infantry Regiment (medium tanks) and, subsequently, the 1st Armored Division's 69th Armored Regiment during intensive training maneuvers in the United States in 1941, and the M2 design continued to prove useful in a basic training role for tank crewmen.