[i] [ii] Leyland Motors, under the direction of the Fighting Vehicles Research and Development Establishment (FVRDE) at Chertsey, was asked to develop an opposed-piston two-stroke diesel of similar design to those previously produced by Napier[iii] and Tilling-Stevens, the latter's Commer TS3[iv] engine being particularly highly regarded.

[vi] One of the reasons the L60's unusual configuration was chosen was so as to obtain as compact a power plant as possible so allowing the height of the vehicle to be kept as low as was practicable, a requirement for the Chieftain's design philosophy which was also seen in the recumbent driver's position.

Scavenging, necessary in a large two-stroke diesel for evacuating the cylinders of exhaust gases, was performed by a Roots blower.

The requirement for an easily changeable engine pack was the result of a British Army analysis of previous tank battles that concluded that a likely future tank battle would last no longer than two hours and so the most demanding requirement expected for any tank engine during wartime would be for it to be run at full power for this total amount of time only and so it would then be advantageous for it to be removed from the vehicle after the battle and exchanged for a fresh engine within a minimum of time.

Sundance had been preceded by "Dark Morn", "High Noon", and the initial "Fleetfoot" engine development programme -the person responsible for the choosing of code names apparently being an admirer of Western film.

Initially, due to unfamiliarity with the two-stroke engine's different exhaust note and power band compared to a four-stroke engine, and with the resulting difficulty in choosing the correct gear required for the particular driving task, trainee drivers tended to under-rev the engines and use inappropriate gear selections, leading to great difficulty climbing gradients, and when the Chieftain Mk 1 was first introduced some drivers had difficulty climbing the vehicle onto the trailers of Thornycroft Antar tank transporters.

The engine was mated with a Merritt-Brown TN12[xiv] triple-differential epicyclic gearbox providing "regenerative" steering, a derivative of the system first used on the Churchill tank.