Tank A1E1, Independent (E1949.331)
The Independent has a number of unusual features; the nearside rear machine-gun turret is capable of firing in the anti-aircraft role by exrta elevation of the gun. An American design of Inertia starter is incorporated and there is a pointer device, driven off the turret ring, that shows the tank commander which way the main turret is pointing in relation to the direction of the tank.
It is claimed that, in order to improve steering, sections from the barrel of a 16 inch naval gun were used to create exrta strong steering brakes. Walter Wilson's modifications to improve steering resulted in a major rebuild of the rear end, a change of drive sprockets and a strengthening axle between the sprockets.
Precise Name: Tank, Independent
Other Name: A1E1
The Independent was a remarkable machine. Fitted with five turrets, it was considered to be a ‘land battleship’. The concept of a tank with multiple turrets influenced designers overseas, notably in the Soviet Union, where the multi-turreted T28 and T35 saw limited service during the German invasion in 1941.
The Independent originated in 1922 with a War Office specification for a heavy tank. This called for a tank with a low silhouette; a rear mounted engine and the ability to cross a trench 9 feet (2.8 metres) wide. It was to be armed with a three-pounder gun mounted in the nose and two machine guns fitted to side sponsons. This was, essentially, an updated version of the World War I Mark V tank.
Vickers were invited to design a tank to the War Office specification. However they also produced an alternative design with a dome shaped turret for the three-pounder, surrounded by four smaller turrets, each of which was fitted with a machine gun. Both designs were submitted to the War Office in March 1923.
Eventually, in September 1926, the War Office decided to adopt the Vickers design. The new tank was to be used for ‘independent action’ and to ‘work in conjunction with cavalry’. The prototype was delivered in October 1926, so construction work had clearly started well before the order was officially announced. The engine, a 350hp air-cooled Armstrong Siddeley V12, was ordered in August 1926. The drive train used a Swiss Winterthur gearbox. This had oil operated synchromesh which did not need a clutch and drove two compound epicyclic gears inside the track sprocket wheels.
The steering was quite advanced. The epicyclic gears were hydraulically operated and servo assisted. Large radius turns used a steering wheel while tight turns were made with a lever operated clutch and brake mechanism. The Independent was only 9 feet wide to fit within the railways’ loading gauge. It also had a relatively long length of track in contact with the ground, and this combined with the narrow distance between the tracks might have made it difficult to steer. The test reports do not mention any problems with the steering.
The Independent was well armoured by contemporary standards. The armour around the crew compartment was 28mm thick and varied between 13mm and 8mm elsewhere. In its original form the Independent weighed 29 tons and could reach 20 mph (33kph) on roads. Its fuel consumption was about a gallon per mile, although the engine also burnt about 4.5 gallons of oil per hour!
The new tank took part in a fire power demonstration for a conference of the Prime Ministers of British Dominions in November 1926. It was described as Britain’s latest and most secret heavy tank. After extensive trials numerous minor faults were found. The rubber tyred return rollers were changed to steel ones and the brake linings altered to use a new material developed by Ferodo. The new brakes were so effective that the stresses that they set up were found to be causing the suspension to separate from the hull.
There were difficulties with the transmission and W.G. Wilson was called in to revise the design. Following his advice the transmission was rebuilt in 1928. Simple, two speed, epicyclic gears were mounted inboard of the drive sprockets. The gears were connected to the sprockets by flexible couplings. These changes increased the weight to 31.5 tons.
The excessive oil consumption of the engine was never resolved and after much development work the whole project was finally abandoned in 1935. The Independent was then retired to the Royal Tank Corps at Bovington Camp where it allegedly formed part of the Camp’s defences in the summer of 1940. It found its way to the Tank Museum in 1949.
The A1E1 Independent was, in many ways, a ‘white elephant’. Tanks with multiple turrets proved to be a tactical liability as it was impossible for the commander to direct the fire of more than one turret. The Independent compared unfavourably with the Vickers Medium Tank (see E1949.330); the Medium Tank carried a similar armament but weighed 19 tons less. The War Office appeared to be uncertain about its role: was it a prototype of a new heavy tank or merely an experimental programme? In either case it was a very expensive project. The engine cost £27,000 and whole programme swallowed up £150,000.
Summary text by Mike Garth