The Medium Tank A6 was designed in an attempt to replace the existing Vickers Medium Tanks Mk I and Mk II but was abandoned because of expense.
In July 1926 the War Office issued a specification for a new medium tank. It was to be armed with two independent machine gun turrets, weigh less than 16 tons, have a main gun capable of penetrating enemy armour at 1,000yds, heavy belly armour for when it crested a hill, fuel tanks outside the hull and to be as quiet as possible. Vickers was selected to develop this tank.
The basic layout of the A6 had the engine and transmission at the rear and the fighting chamber at the front, with the two auxiliary turrets at the very front of the tank and the main turret just behind them. The main turret was circular, with slightly sloped sides. The rear deck then sloped gently down from the back of the turret to the rear of the tank. The tank weighed 17.5 tons, three tons heavier than predicted by Vickers, and this was without the rear machinegun turret originally planned. Engine power had to rise in response, so the 120hp engine of the original plans was replaced with a 180hp model. Two mild steel prototypes were made in just under a year, followed by a third and final prototype.
The first prototype (A6E1) was powered by a 180hp Armstrong-Siddeley V-8 engine. The main turret carried the 3pdr main gun and one .303in Vickers machine gun. The two auxiliary turrets each carried two Vickers machine guns. The main turret had two cupolas, side by side. Suspension was of the box bogie type.
The second prototype (A6E2) was very similar. It was originally built with a 180hp Ricardo CI diesel engine, but was later given a 180hp Armstrong-Siddeley engine.
The third prototype (A6E3) used the Armstrong-Siddeley engine. The auxiliary turrets were redesigned, and only carried one .303in gun each. The main turret only had a single cupola. Suspension was of the Horstman type. In tests during 1937 the A6E3 was given a much more powerful 500hp Thorneycroft RY 12 engine.
In 1930 it was decided to end the direct development of the A6, which was seen as too costly. Vickers moved on to the slightly lighter Medium Tank Mk III, while the three A6 prototypes were used for a series of experiments that continued until 1938.
Medium Tank, A6
Production: Three prototypes
Hull Length: 21ft 6in
Hull Width: 8ft 9in
Height: 9ft 2in
Weight: 17.4 tons
Armament: One 3pdr QF gun, five Vickers .303in machine guns (three on A6E3)