The Medium Tank Mk III followed on from the Medium Tank A6 and was designed to replace the earlier Medium Tanks Mk I and Mk II, but like the A6 it was considered to be too expensive and was abandoned in favour of the lighter A9, which became known as the Cruiser Tank Mk I.
The A6 had been developed in 1928-30. It had a circular main turret mounted close to the front with two auxiliary machine gun turrets at the very front of the tank. It was powered by a 180hp Armstrong Siddeley V-8 engine, and in its final version armed with one 3pdr gun and three Vickers machine guns. Although it was seen as a promising design, the A6 was heavier than expected and was judged to be too expensive.
In 1930 work moved on to the Medium Tank Mk III. In layout this was very similar to the A6, with the engine and transmission at the rear, auxiliary turrets at the very front and the main turret just behind them. It differed in having a large extension at the back of the otherwise circular turret to carry radio equipment. The commander's cupola was modified, the gun mountings improved, new steering brakes were developed and the weight was reduced. Three prototypes were produced, but in the harsh economic conditions of the early 1930s the Medium Mk III was still seen as being too expensive. Work moved onto a lighter model, originally designated as the Medium Tank Mk IV, but that eventually became the A9 Cruiser Tank Mk I.
Medium Tank Mk III
Production: 3 prototypes
Hull Length: 21ft 6in
Hull Width: 8ft 10in
Height: 9ft 8in
Weight: 16 tons
Engine: 180hp air-cooled Armstrong-Siddeley V-8
Max Speed: 30mph
Armament: One 3pdr QF gun, three Vickers .303in machine guns (one in main turret, two in auxiliary turrets)