The Christie M1928 was the first armoured vehicle to use the famous 'Christie suspension', and was thus the origin of a large number of later tanks.
Christie's first attempt to produce a tank capable of operation with or without tracks, the Christie Medium Tank M1919/ M1921, had ended in failure, with the M1921 found to be unreliable and hard to manoeuvre.
Christie returned to the drawing board, and came up with a new suspension system, which he installed on the M1928. The new system used four large road wheels on each side of the vehicle. Each wheel was carried on a pivoting arm, which was supported by a large coil spring. Each wheel also had two solid rubber tires (with a gap between them), which added a further level of suspension and also reduced road noise.
Power went to rear drive wheels, which were raised off the ground. When the M1928 was operating without its tracks, chains linked the drive wheels to the rear road wheels to provide power.
The tracks used square shoes, 10in wide and 10in long. Every other shoe had a large tongue on the inside that engaged with rollers inside the drive wheels. The tongues also ran between the twin tires on the road wheels. It took 30 minutes to change between wheel and track running.
The rest of the vehicle was fairly basic. It had the engine at the rear, the fighting compartment in the middle and the drive at the front. There was a pedestal mount for a machine gun in the crew compartment and a mock-up of a gun in the nose, but the M1928 was really produced to demonstrate the new suspension.
The M1928 was originally shown at Fort Myer, Virginia, on 28 October 1928. It then underwent tests with the Tank Board, and on 19 November 1928 managed an average speed of 28mph on a run from Fort Mead to Gettysburg, going one way on tracks and the other on wheels. In ideal circumstances it could reach an impressive 70mph on wheels and 42.5mph on tracks.
The Army was now interested in ordering tanks based on the Christie design, but the order was delayed by a dispute between Christie and the Ordnance Department over the specifications for the new vehicle (this would be typical of Christie's relationship with the Army, and would eventually lose him the contract for later models). In this case the arguments were smoothed over, and Christie received a contract to produce one M1931 tank. This was delivered on 19 January 1931, and after more delays Christie was given a contract to produce seven more tanks on 12 June 1931. These were similar to the M1931, but were given the official specification Convertible Medium Tank T3.
The Soviet Union also ordered two Christie tanks, which became the basis of the massive BT series of tanks, which saw extensive combat during the Second World War.
Hull Length: 17ft
Hull Width: 7ft
Weight: 8.6 tons
Engine: Liberty V-12, 338hp
Max Speed: 42mph tracks, 70mph wheels
Armament: mock-up only