By the Mark V, the design was more or less optimised and it was the final development of in the form of the Light Tank Mk VI which was chosen for the British Army expansion programme in expectation of war.

Following the activities of the Experimental Mechanized Force in the late 1920s, the British Army identified a need for two light tracked vehicles; one to carry a machine gun for the infantry and one with a turret for the Royal Tank Corps.

[2] The Carden-Loyd tankette became the infantry vehicle, at the same time Carden privately developed a number of light, two-man tank designs.

The Mark VII was a small machine gun-armed vehicle with a 59 hp (44 kW) Meadows engine which gave it a maximum speed of 35 mph (56 km/h).

Considered a reconnaissance vehicle and a mobile machine gun position, the Mark VI was the final stage of development of the Carden-Loyd series of tankettes.

The bevelled turret was replaced by a cylindrical design but still carried a single 0.303 Vickers machine gun.

The track was tensioned by a rear idler—which, being set at the same height as the drive sprocket, was new in British tank designs—and returned over three rollers.

[3] The Mark IA tanks sent to India in 1931 for trials received modifications to improve engine cooling in the hotter climate and various means were experimented with to reduce the heat for the crew as well.

The Mark II used a 66 hp (49 kW) Rolls-Royce engine which was, along with the Wilson preselector gearbox and transmission, on the right-hand side of the tank.

This design, invented by Sidney Horstmann and exclusively used on lightweight vehicles, was also used up to the Light Tank Mk VI.

Power came in the form of a Henry Meadows six-cylinder petrol engine, producing 88 hp (66 kW), coupled with a four-speed preselector gearbox.

They were sent to the North-West Frontier of India and took part in the 1936-1939 Waziristan campaign against the fiercely independent Pashtun tribesmen that inhabited that mountainous region.

They were led by the religious leader Mirzali Khan and deployed guerrilla tactics of ambush and were not drawn into a decisive battle with the well trained and numerically superior British troops.

This unusual level of co-operation between manufacturer and user led to rapid resolution of problems and implementation of improvements.

It also had a three-man crew but a larger turret to accommodate a radio set and had an 88 hp engine for higher speed, despite the heavier weight.

Buyers included Finland, Lithuania, Latvia, Argentina, Belgium, Switzerland, the Dutch East Indies and China.

Armed with a French 13.2 mm Hotchkiss machine gun, they were designated Char Léger de Reconnaissance Vickers-Carden-Loyd Mod.1934 T.15 by the Belgians.