1944. Tetrarchs did not see any further combat and were deemed obsolete by 1946; the last was retired in 1950. There were several variations on the Tetrarch design, including the Alecto self-propelled gun and the Light Tank Mk VIII but none of these were used operationally by the British Army. Development history Initial development 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 main gun paired with a Besa machine gun, and mounted the two guns in a two-man turret. The tank possessed a maximum of of armour. The prototype weighed approximately and was powered by a Meadows engine. Suspension was on eight road wheels, four per side, with no separate driver or idler wheels and it was capable of a 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. The War Office examined the design and put the prototype through a series of trials during May and June 1938; the model was tested as a possible "light cruiser" since War Office light tank needs were already met by its predecessor, the Mark VI. The War Office then took the view that the tank was not acceptable as a light cruiser because the Nuffield A13 offered better speed and obstacle crossing performance. Despite this, it was decided that it was essential for some Tetrarchs to be produced, and it was suggested that they be brought in at the end of