The Christie Medium Tank M1921 was a greatly modified version of the earlier Christie Medium Tank M1919, and was a turretless tank designed to be operate with or without its tracks.
The M1919 was Christie's first attempt at a wheel or track tank. It had four main road wheels, which could be used alone without tracks. A two wheel bogie was carried on the middle of each side, and could be raised for trackless running or lowered when tracks were in use. The M1919 carried a circular turret armed with a 57mm gun and coaxial machine gun, and a second machine gun in a domed turret on top of the main turret.
The M1919 was delivered to the Aberdeen Proving Grounds in February 1921, and underwent tests until 21 April 1921, when the programme was suspended at Christie's request, so that he could make some modifications to the design. The Ordnance Committee agreed to fund these changes on 15 June 1921, and the modified vehicle was returned to the Aberdeen Proving Grounds on 28 March 1922, this time as the Christie Medium Tank M1921.
The M1921 was a significantly different vehicle to the M1919. The turret had been removed, and a larger hull structure installed. The combination gun mount from the turret had been installed in the front of the hull, and two more machine guns were carried on the front corners of the hull. The crew was increased from three to four, with the two gunners in the nose and the driver and command in the centre. Fuel capacity was increased.
The suspension was also modified. The rear drive wheels were unchanged, and remained un-sprung, with holes for the track teeth to engage. The front wheel was mounted on coil springs installed in the sides of the front hull. The two-wheel bogie was replaced with two larger road wheels (still smaller than the main wheels) carried on a single pivoting bogie.
The M1921 underwent tests from March/ April 1922 until 24 October 1922. During this period it drove 341.5 miles, with 161 of those on tracks. It then went to Camp Meade for another 66 miles of tests. These tests showed that the M1921 was unreliable, difficult to manoeuvre and inefficient in combat due to the small fighting compartment. The sole prototype was sent to the Automotive Museum at the Aberdeen Proving Grounds on 10 July 1924.
Over the next few years Christie worked on a number of amphibious designs, before returning to tank design with the Christie M1928, the first design to use his famous 'Christie Suspension'.
Hull Length: 18ft 2in
Hull Width: 8ft 6in
Height: 7ft 1in
Weight: 14 tons
Engine: Christie 6-cylinder 120hp water-cooled
Max Speed: 14mph on wheels
Armament: One 57mm gun, three machine guns