The Christie suspension is the name of a suspension system developed by American engineer J. Walter Christie (1865–1944) for military vehicles, especially tanks. This system allowed for considerably longer movement than the leaf spring system, which was commonly used at the time. Aside from faster maneuverability, the Christie suspension used individual road wheels with tyres that allowed a tank to be used without treads.
thumb|A T3E2 tank with Christie suspension system crossing an obstacle during tests in 1936.
History
J. Walter Christie, an American engineer and inventor, envisioned a lightweight tank with long range capabilities and high speed that were designed to penetrate enemy lines and attack their infrastructure and logistics. His first prototype of 1919 could be driven on its wheels to get to the desired point and have its tracks quickly fitted on at its destination. This prototype, designated as the Christie Model M1919, was delivered to the U.S. Army for testing, which was then approved on 8 June 1920. Christie later proposed another modification to add coil suspension to the front wheels of the tank and removed the turret, relocating it to the nose of the tank. The modified tank, designed M1921, debuted in 1922 but was rejected this time as it was deemed unsafe and unreliable due to lacking in maneuverability and internal space. These tanks, known as the Christie M1931, were designated as Convertible Medium Tank T3, with four given to the cavalry for testing. These prototype tanks were labelled as "agricultural tractors" during the sale, and were shipped turretless to the USSR. The Soviets inspected and reverse engineered Christie's prototypes, leading to the creation of the BT series of light tanks. The system was eventually scrapped in favour of a torsion bar suspension system which was introduced on the T-34/85. Like the earlier deal with the Soviets, the prototype tank was labelled as a farm tractor and shipped to Britain, with other parts that had to be dismantled being shipped under the label "fruits."
thumb|Earlier models of the T-34 medium tank featured Christie suspension, until it was replaced by torsion bar suspension in later models.
Although the Christie suspension system was never actually sold to Poland, Polish designers managed to create their own form of suspension system based on technical sketches that were obtained from Christie's company. This new system was used in the development of the 10TP cruiser tank that never made it past the prototype stage. This allowed for vertical movement of the wheels, enabling the tank to go at higher speeds on rough and rugged surfaces. Another feature of the Christie suspension was the wheels, which were fitted with rubber tyres and could function as regular road wheels without the need for treads, allowing a tank with damaged treads to have its treads removed and still be functional.