The prototype of the Light Tank Mk VII ( A17 ) , nicknamed ' Purdah ' , was first developed in 1937 by Vickers @-@ Armstrongs as a private venture , and was intended to be sold either to the British Army or to foreign militaries . It was to be the latest in a series of light tanks produced by the company . The tank was designed to overcome the shortcomings of insufficient armament in earlier light tanks that were fitted only with machine guns . Vickers @-@ Armstrong installed on the Mk VIIs a 2 @-@ pounder 40 @-@ millimetre ( 1 @.@ 6 in ) main gun paired with a 7 @.@ 92 @-@ millimetre ( 0 @.@ 312 in ) Besa machine gun , and mounted the two guns in a two @-@ man turret . The tank possessed a maximum of 14 millimetres ( 0 @.@ 55 in ) of armour . The prototype weighed approximately 16 @,@ 800 pounds ( 7 @,@ 600 kg ) and was powered by a 165 @-@ horsepower ( 123 kW ) Meadows engine . Suspension was on eight road wheels , four per side , with no separate driver or idler wheels and it was capable of a 40 miles per hour ( 64 km / h ) top speed . The Mk VII design relied on an unusual steering method and a mechanical system incorporated into earlier Vickers models . The front wheels could be steered to allow for gentle turns by bending the tracks . For sharper turns , the system returned to the conventional method of braking one track to turn the tank ; the dual system of turning was designed to lessen mechanical strain on the MkVII and reduce its power wastage . The suspension system was also a new design that relied on struts with pockets of air for springing and cushions of oil for damping , and each of the wheels was independently sprung .