In 1934 Rock Island Arsenal began building a series of Track-or-Wheel convertible vehicles using light and medium tanks chassis. These Combat cars had steering wheels and rubber covers for them. The T4E1 (July 1934) was the first modification of the T4 prototype from which it differs for sponson boxes, squared hatches and a completely new turret derived from the M1 Combat Car one. Although it had a crew of only four members ( a driver, two gunners and a Commander ) it was armed with six machine guns. A .50 caliber and a .30 caliber were mounted inside the turret. Three other .30 caliber were placed at the front of the main body and another one at the rear of the turret, in an anti-aerial position. The Engine was a 7 cylinder Continental that could reach 44 miles per hour on wheels and 30 on tracks.