Editing Rolls-Royce Meteor (section)

===Engine design===

{{main article|Cromwell tank#Development}}

Development started with the use of recovered Merlin engine parts from crashed aircraft.  They were unsuitable for re-use in aircraft, but the Rolls-Royce chassis division had begun collecting and refurbishing them in the hope of finding a use.  Robotham was approached by Henry Spurrier, of Leyland Mechanization and Aero, to ask about help with tank powerplants.  Based on Spurrier's requirement, the first prototype Meteor engine (and subsequent production of Mark 1 engines) was assembled on the basis of recovered Merlin parts.

The major change for tank use was to reverse the direction of engine rotation.  Automotive gearboxes ran the opposite way to an aircraft propeller and changing direction required modification of the camshaft lobes (most Merlins were "right-hand tractor", i.e. the propeller rotated clockwise when viewed from the rear).<!-- from Merlin article under variants -->  For the Meteor, the Merlin [[supercharger]], reduction gear and other equipment were removed from its crankshaft, greatly simplifying its construction.  Many aircraft-specific parts were deleted, such as the propeller reduction gear and the aircraft-style starter. That meant the dimensions of the engine became similar to the [[Liberty L-12|Nuffield ''Liberty'']] engine, and it would fit into the space for the Liberty Mark VI version in the [[Crusader tank]]. It retained the Merlin dual ignition system — each cylinder had two [[spark plug]]s, driven from separate [[ignition magneto|magnetos]].

[[File:Crusader tank III.jpg|thumb|A Crusader tank, similar to as used in trials]]

On 6 April 1941, the first Merlin prepared for tank use was despatched to Aldershot in a modified Crusader tank, which was tested on the Army standard speed course behind Farnborough.<ref>{{cite web|url=http://www.rrec.org.uk/History/Clan_Foundry_Belper.php |title=Rolls-Royce Enthusiasts' Club – Clan Foundry Belper |publisher=RREC |access-date=2010-12-01}}</ref> A "maximum revolution recorder" recorded "something in excess of {{convert|50|mph}}". 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. Some spectators by the course took fright, running away and leaping over a hedge. 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.{{sfn|Robotham |1970|pp=150,151}} So the concept was proved, surpassing all expectations.

The engine was commissioned for use in the new [[Cromwell tank]] and changes were made to the Cromwell development programme to accommodate it. To enable fitting it in-line with a [[David Brown Ltd.|Merrit-Brown]] gear (and steering) box, the engine was lowered.  A new flat sump was created, the oil pumps changed and the crankshaft lined up with the new gearbox.  The new engine had cast pistons, rather than forged ones, and was de-rated to around 600&nbsp;bhp (447&nbsp;kW), running on lower-[[octane rating|octane]] [[pool petrol]] instead of high-octane [[avgas|avgas (aviation fuel)]]. [[British Thomson-Houston]] (BTH) magnetos were changed for Simms units.