In September Vickers, given the order to build a prototype, proposed a first design based on the Vickers A1E1 Independent, with the fighting compartment in front and the engine compartment at the back. There would be a central two-man turret with a 3-pounder and a coaxial machine-gun; it was intended to house the commander and a special observer, with a cupola each. In the front of the hull were to be placed two secondary machine-gun turrets, each with a twin Vickers machine gun. A third machine-gun turret was intended to be mounted at the back of the vehicle, behind the main turret, which would be armed with an anti-aircraft (AA) weapon. A crew of seven men was needed. Maximum armour would be and basis armour , limiting the weight to fourteen tons. Riveted plates were used. The total fuel supply would be : ten in a small tank inside, gravity feeding the engine; the remainder in external tanks on the fenders. Two engine options were indicated a engine would allow for a speed of and a engine would raise this to .