It was a result of co-operation between Leyland Motors and Rolls-Royce who between them in 1941 had suggested that a specialised de-rated version of the Merlin aero-engine would be highly suitable for use in armoured fighting vehicles.

While unsuitable for re-use in aircraft, the Rolls-Royce chassis division had begun collecting and refurbishing them in the hope of finding a use.

For the Meteor, the Merlin supercharger, reduction gear and other equipment were removed from its crankshaft, greatly simplifying its construction.

It retained the Merlin dual ignition system — each cylinder had two spark plugs, driven from separate magnetos.

The officers with stopwatches at each end of the run were meant to signal each other by dropping handkerchiefs, but were so nonplussed that neither got a timing.

The corporal driving kept his foot down, and failed to take a corner on the run-off section at the end, decapitating a telegraph pole and spreading coils of wire in all directions.

The new engine had cast pistons, rather than forged ones, and was de-rated to around 600 bhp (447 kW), running on lower-octane pool petrol instead of high-octane avgas (aviation fuel).

It would deliver only 350 hp (260 kW), but Leyland was concerned with the problem of sufficient cooling for the Meteor within the confines of the tank engine bay.

Hives took the problem to the Ministry of Supply, telling Lord Beaverbrook that he already had his hands full making Merlin aero engines, and Rolls-Royce would want £1 million to its credit and 'no interference' to make tank engines, The Beaver telegrammed back:[6][7] OHMS Ministry of Supply to W. Hives Nightingale Road Rolls-Royce Derby The British Government has given you an open credit of one million pounds.

The Meteor was initially produced by Rolls-Royce but manufacturing capacity was severely limited due to the demand for Merlin engines.

Because weight saving was not so important for a tank engine, some of the Merlin's more expensive light-alloy components were replaced with cheaper, steel versions.

[8] Many of these rejected parts while not meeting strict standards for airworthiness, were perfectly adequate for use in ground vehicles where the crew or operators were not subject to the inherent hazards involved in flight.

In this role, Rover continued the development and production of the Meteor Mk IVb and various derivatives, including the Meteorite V8 and the M120 V12.

Replacing the earlier Liberty L-12 licence-built by Nuffield and used in the Crusader, the Meteor engine in the Cromwell tank provided almost twice the performance in virtually the same 1,650-cubic-inch (27.0 L) displacement.

W. A. Robotham was surprised and pleased when in 1963 Duncan Sandys said "I regard the adoption of the Meteor tank engine as the absolute turning-point in the history of British tank development", at the opening of the Rolls-Royce aero engine factory at East Kilbride.