Horstmann suspension, also known as Horstman, Vickers-Horstman and rarely Slow Motion, is a type of tracked suspension devised by British tank designer John Carden and worked into a production design by engineer Sidney Horstmann. First used on the A6E3 Medium Tank prototype in 1935, it proved far superior to previous suspensions from Vickers. It was widely used on World War II-era tank designs but in the post-war era was increasingly limited to British tanks as newer systems emerged in other countries. The last tank to use this basic mechanism was the Chieftain, designed in the late 1950s. Horstman Defence Systems remains a tank suspension specialist to this day and makes a range of systems based mostly on torsion systems with hydrodynamic damping. They are also referred to as "Horstman suspensions" although they have no details in common with their earlier designs. History Sidney Horstmann became interested in suspension designs in the 1920s as part of his efforts to improve the ride of the cars being built in Bath by his Horstmann Cars company. This led to a new design using multiple coil springs in suspension, and the creation of the Slow Motion Suspension Company to sell the design to all makers. Horstman Cars went bankrupt in 1929, leaving Slow Motion a going concern. In 1934, John Carden of Vickers-Armstrongs had a "bright idea" for a new type of tank suspension and partnered with Horstmann's Slow Motion to turn it into a working design. At the time, the British Army was testing, largely to their dislike, the A6 series medium tank prototypes. Among their many problems, the Vickers-supplied "box" suspension proved to be very springy and led to the tank rocking for some time after firing the main gun. The new design used two road wheels on a single bogie, each connected to a bell crank with a horizontal coil spring between the crank arms, and double-acting shock absorbers to control recoil. This was fitted to the A6E3 between February and April 1935 and immediately proved to dramatically improve stability. E3 had also been fitted with a more powerful 500 hp Thornycroft RY/12 marine engine in an effort to improve performance, but in testing, this showed no benefit and ultimately only three examples of the Medium Mark III were produced. Several other medium tanks, including the A9 and A14, used the same design. Carden was killed in an air crash in