Development for this tank started in 1937 by Vickers-Armstrongs privately as the Light Tank Mk VII and nicknamed the Purdah. The trials tested the tank's ability to act as a "light cruiser", but this failed as the A13 cruiser was much better at the task. Thus, it was suggested that the Mk VII be tested as a light tank instead and production to be started for the trials. The Tetrarch was first issued in November 1940 to the 1st and 6th Armoured Division, the 1st had lost most of their equipment in the Battle of France and the 6th was a newly formed unit. While these units were sent to North Africa, the defects in the engine cooling system forced the Tetrarchs to stay behind, until they were taken out of armoured divisions due to the "light tank" concept becoming obsolete. Most of the Tetrarchs were shipped overseas and the Soviet Union compared their role to that of the T-70 light tank, they were mainly used for reconnaissance and for airborne operations.

It was introduced in Update 1.55 "Royal Armour" along with the initial British ground tree. A light tank with a 2-pounder, it fits the British light line of a fast tank with a powerful gun but weak armour. The Tetrarch plays like any other Rank I vehicle in the game. Zip around with high speed to the destination and get a first shot off on the enemy tank (preferably the gunner). The 2-pounder can penetrate most enemy tanks at close range and the 40 mm shells can cause a decent amount of shrapnel that can damage most of the internals at the area of the penetration. The mobility is great with the adequate horsepower to propel the 7 ton tank around. The armour is barely adequate for Rank I, with its flat surfaces encouraging penetration with the cramped interiors making one-hit destruction a worrying situation for the Tetrarch.