Cromwell tank
The Cromwell tank, officially Tank, Cruiser, Mk VIII, Cromwell , was one of the series of cruiser tanks fielded by Britain in the Second World War. Named after the English Civil War–era military leader Oliver Cromwell, the Cromwell was the first tank put into service by the British to combine high speed from a powerful, reliable engine and reasonable armour. The intended dual-purpose high-velocity gun could not be fitted in the turret, so a medium-velocity dual-purpose gun was fitted instead. Further development of the Cromwell combined with a high-velocity gun led to the Comet tank.
The name "Cromwell" was initially applied to three vehicles during development. Early Cromwell development led to the creation of the A24 Cavalier. Later Cromwell development led to the creation of the competing Centaur tank. This was closely related to the Cromwell, both vehicles being externally similar. The Cromwell and Centaur tanks differed in the engine used; the Centaur had the 410 hp Liberty engine, the Cromwell had the significantly more powerful 600 hp Meteor; Centaur hulls were converted to Cromwells by changing the engine.
The Cromwell first saw action in the Battle of Normandy in June 1944. The tank equipped the armoured reconnaissance regiments of the Royal Armoured Corps, in the 7th Armoured Division, 11th Armoured Division and the Guards Armoured Division. While the armoured regiments of the latter two divisions were equipped with M4 Shermans, the armoured regiments of the 7th Armoured Division were equipped with Cromwells. The Centaurs were not used in combat except for a few fitted with a 95 mm howitzer, which were used in support of the Royal Marines during the amphibious landings of Normandy.
Development
Initial designs: A23, A24
Development of the Cromwell and Centaur dates to 1940, as the Crusader tank was being readied for service. The General Staff were aware that the Crusader would become obsolete, and in late 1940 they set out the specifications for a replacement tank, expected to enter service in 1942, fitted with the QF 6 pounder gun.Vauxhall responded with the A23, a scaled down version of their A22 Churchill infantry tank. This would have had 75 mm of frontal armour, used a 12-cylinder Bedford engine, carried a crew of five and would have had the same suspension as the A22.
Nuffield submitted the A24, heavily based on its Crusader design and powered by its version of the Liberty engine, a V-12 design dating to the late days of World War I and now thoroughly outdated. Nevertheless, as the design was based on the Crusader, it was expected it could be put into production rapidly.
The final entry was from Leyland and Birmingham Railway Carriage & Wagon. Their design was similar to the Nuffield, but with different suspension and tracks.
The designs were received and examined in January 1941, with Nuffield's A24 being declared the winner on 17 January. Six prototypes of the Cromwell were ordered for the spring of 1942. These arrived four months late, and by this time the design was already outdated. It was put into production anyway, but in service it proved underpowered. Only a small number were built.
Delays in the A24 program led to demands to get the QF 6 pounder into service earlier. This led to a series of up-gunned Crusaders mounting the 6 pounder.
Introduction of Meteor engine
With the start of the war, Rolls-Royce ended car production and set up a design team looking for other ways to use their design capability. The team formed under the direction of W. A. Robotham at Clan Foundry in Belper, north of Derby. They began recovering and refurbishing parts from crashed Merlin engines with the intention of using them for non-aviation purposes.In October 1940, Robotham met Henry Spurrier of Leyland Motors to discuss British tank design. The Tank Board desperately needed a more powerful tank engine to replace the aging Liberty. Robotham and Spurrier decided to attempt to fit a refurbished and re-worked Rolls-Royce Merlin engine to a Leyland tank for testing. Design had three priorities:
- To remove the supercharger and make the engine operate on standard fuel;
- To fit the engine into a current Crusader tank so the engine, and the remaining elements of the tank could be tested under greater load;
- To improve the cooling system such that the larger output engine could be cooled in the same space.
Delivered to Aldershot on 6 April 1941, the test team had trouble timing its runs because it was so fast, estimating it reached. Leyland arranged to start production of 1,000 examples of the engine as the Meteor.
With engine power doubled, it soon became apparent that the additional stresses placed on the Crusader components required significant re-work to increase reliability. Leyland had no spare capacity, and re-work commenced with the help of BRC&W. It was planned to fit this to BRC&W-built versions of their original A24 submission.
Design splits, and production commences: A24, A27L, A27M
Refitting the design of the A24 Cromwell for the Meteor engine was not acceptable to Nuffield, and hence a new specification of tank was created working with Leyland, the A27 Cromwell.In mid-1941, Leyland changed its mind, concerned about cooling problems. This was a major concern for the Tank Board, as cooling issues had been a major problem for the previous generation of Crusader and Covenanter tanks. The Tank board was still committed to the Meteor, but to avoid dedicating all resources into a potentially flawed design, the design was split into three separate vehicles:
- A24 Cromwell I under Nuffield, later known as "Cavalier". This was based on the existing specification of Liberty engine and Wilson steering, working from experience learned with the Crusader.
- A27L Cromwell II initially under English Electric, but design taken over by Leyland, later known as "Centaur". This was to be based on a revised and upgraded Liberty engine from Morris Motors and the newly available Merrit-Brown gearbox as used on the Churchill tank.
- A27M Cromwell III under BRC&W, which carried the Cromwell name through to production and service. This was to be based on the new Meteor engine and the Merrit-Brown gearbox, but was also to be designed such that the Liberty engine could be fitted if problems arose.
While Leyland continued with the Liberty under A27L, the Tank Board continued with the Meteor engine by placing an order directly with Rolls-Royce. Leyland also suggested using a diesel engine of their own design, although this was later abandoned. BRC&W became parent to the Cromwell in September 1941 working with David-Brown RR and Leyland and produced a pilot in January 1942.
Cromwell's cooling system was a new design and put through over nine months of testing in a variety of configurations. This included the development of new fan drives and inlet louvres, which can be seen on the Cromwell's engine deck. The resulting system for a Meteor-powered tank delivered both the necessary cooling performance, and reduced the power lost in driving the cooling system from 90 to 30 hp. ‘To Fred Hardy, the chief development engineer at Rolls Royce Belper, must go the credit for originating the design which finally solved the problems. It was an outstanding piece of engineering’. This made the performance improvement of the Meteor over the Liberty even more pronounced and left room for expected development of the A27.
The first prototype of a Meteor-powered A27M Cromwell was delivered to the Army for trials in March 1942, several months before the A24 that was supposed to precede it, and also prior to the A27L Centaur pilot vehicle which was delivered in June 1942. With nearly it proved to be exceptionally mobile when tested.
Orders were placed for both A27L and A27M versions as there were concerns about the production rate of the Meteor. Design also commenced on a 17-pounder armed version under specification A30, leading to parallel development of the A30 Challenger.
As all of Rolls-Royce's production capacity was engaged in producing the Merlin engine for aircraft, production of the Meteor version was initially based solely on parts recovered from crashed aircraft, with many engines still showing crash damage. Additional sources for manufacturing the Meteor engine were investigated. Even when assigned reduced production quotas, BRC&W proved unable to meet the demand for Cromwell, and Leyland became the design and production parent of both the A27L and A27M versions including subcontracted work.
Engine production
Rolls was at this time having trouble meeting demand for the Merlin, let alone the Meteor. Rover was having trouble turning Frank Whittle's Power Jets W.2 jet engine design into a production engine due to increasing animosity between the engineers at Power Jets and Rover. Things became particularly heated when Whittle learned that Rover had set up a secret project to develop a simpler-to-produce "straight-through" version of the W.2. Whittle had, though Stanley Hooker of RR's supercharger division, been in contact with Rolls for help delivering some of the required parts that Rover proved unable to produce.At the same time MAP was frustrated with Power Jets' complaints about Rover and the lack of a usable engine and had proposed in December 1942 that RR take over Power Jets but were not in a position to force such an event. The solution came in an agreement between Rover and RR. Ernest Hives, the head of Rolls had met Whittle and was fascinated by the jet engine called a meeting with his counterpart at Rover, Spencer Wilks, and the two met late in 1942 at the Swan and Royal pub in Clitheroe. Hives offered to trade the Meteor for the W.2, an offer Wilks jumped at. With approval by the company's boards and the MAP, Rover's jet engine team and production transferred to RR while Rover set up production of the Meteor engine at their Tyseley factory and at an additional line set up by Morris Motors in Coventry.
Production began in November 1942. In August, new names had been given to all three designs; the original A24 Cromwell I became the Cavalier, the Liberty powered A27L Cromwell II became Centaur and the Meteor powered A27M kept the name Cromwell. It would take considerable time for Rover to make ready production lines for the Meteor and it was not until January 1943, that sufficient Meteor engines were available and the A27M Cromwell began production. The official handover of the Meteor and W.2 took place on 1 January 1943.