Horstmann suspension

The Light Tank Mk Ia (A4E8 prototype) became the first tank in the world to use the Horstmann design. In this case the spring is outside the track area, leaving room for track return rollers to lie directly over the suspension in a particularly compact layout.
The Light Tank Mk III introduced a slightly modified version with only one bell crank per bogie, causing the spring to lie somewhat angled as a result. This system was used on the Universal Carrier.

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.