was 18 M2 tanks, and 94 M2A1 tanks, for a total of 112. For combat it was a poor design, with thin armor, inadequate main armament and a high profile. The four sponson-mounted machine guns proved to be completely unnecessary. But it provided important lessons that were used for the later M3 and M4 medium tanks. In particular, the M2's sloped frontal hull armor (glacis plate) was extremely advanced for a 1939 design, and would become a permanent feature of U.S. tank design. Events in Western Europe and on the Eastern Front rapidly demonstrated that the M2 was obsolete, and it was never used overseas in combat; it was used for training purposes throughout the war. Chrysler opened a new tank plant, the Detroit Arsenal Tank Plant, to manufacture the M2, and the US Government contracted in August 1940 for 1,000 vehicles to be produced. As events in Europe made obvious that the M2 was obsolete, the government modified the contract before production began. Instead of M2 medium tanks, the plant would now build 1,000 M3 Grant tanks. Production of the M2 was returned to the Rock Island Arsenal, where 94 M2A1s were eventually built. The M2A1 had slightly better armor and a slightly larger turret than the original M2, since it had the turret from the M3 Light Tank, with gun mantlet armor 2 inches (51 mm) thick. World War II Light tanks M3 Light Tank and M5 Light Tank The M3 Light Tank was an upgrade of the M2 Light Tank. The Battle of France gave momentum to the US tank program because U.S. observers saw how easily British and French light tanks were decimated by the advanced German Panzers, and in July 1940 work began on a new light tank based on the M2 series. The initial upgrade was designated the M3 Light Tank, and it was given thicker armor, modified suspension and a 37 mm gun. Production of the M3 and later the M5 Stuart started in March 1941 and continued until October 1943 with a total of 25,000 produced. An upgrade of the M3, which was initially called M4 but later redesignated the M5, was developed with improved engines and produced in 1942. The M5 featured a redesigned hull and driver's hatches moved to the top. There was the T7 light tank project with thicker armor, volute suspension and better gun. Changes requested in development