In 1934–35, at the request of the Cavalry, three prototype tanks, the T2, T2E1, and T2E2 were produced. Under the terms of the National Defense Act of 1920, tanks were restricted to infantry units. To get around the Defense Act, these tanks were called "combat cars". The M1 series entered service in 1937. The T2, inspired by the British Vickers 6-Ton, was standardised as the M1 Combat Car. The T2E1, a single-turret tank armed with three machine guns, was standardised as the Light Tank M2A1. The T2E2, a two-turret tank with two machine guns, was standardised as the M2A2.