Cromwell tank
The Cromwell tank, officially Tank, Cruiser, Mk VIII, Cromwell (A27M), 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 (the Rolls-Royce Meteor) 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 Tank, Cruiser, Mk VIII, Centaur (A27L) design. The Centaur tank 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 those fitted with a 95 mm howitzer, which were used in support of the Royal Marines during the amphibious invasion 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 was 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 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 (BRC&W). 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. Creation of the 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: They removed the  supercharger from a Merlin Mk. III to downgrade the performance to a suitable level for tank use, reversed the direction of engine rotation to match tank transmissions, and fitted the resulting engine to a Leyland-built Crusader. 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: These early design designations of Cromwell I, II, and III are not to be confused with the later production designations of Cromwell I, II, etc. which were production variants of the A27M. 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. 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 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 hp to 30 hp. 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 (mild steel ) 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. 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. Rover engine production. Rolls was at this time having trouble meeting demand for the Merlin, let alone the Meteor. Meanwhile, Rover was having troubles developing Frank Whittle's Power  Jets W.2 jet engine design 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 lab to develop their own versions of the design. Whittle had, during the same period, contacted Rolls for help delivering some of the required parts that Rover proved unable to produce. A solution to both their problems was offered by Ernest Hives, a Rolls board member, who had met Whittle and was fascinated by the jet engine (Rolls-Royce's major product was piston aero engines). Hives 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. Rover set up production at their Tyseley factory, and an additional line was set up by Morris Motors in Coventry. Production began in November 1942. That month, new names were 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 a few months later, in 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. Possible cancellation, and armaments trouble. To increase production of Meteor engines Rover and Morris required machine tools from the US, which took time to arrive. In the interim, Centaur production continued, to avoid closing Cromwell tank production lines. The Cromwell had originally been intended to mount the high  velocity QF 6-pounder tank gun as primary armour piercing (AP) armament with a few mounting the Ordnance QF 95 mm howitzer to fire high explosive and smoke shells as close support tanks. The earlier introduction of US M3 Grant and M4 Sherman tanks placed a dual purpose 75 mm gun into British and Commonwealth service. The 75 mm could fire a more effective HE shell than the 6-pounder at the cost of a reduction in armour-piercing performance. The 6-pounder firing solely AP shells was a retrograde step. Once the Vickers 75 mm HV gun was seen  to be too big for the Cromwell turret, work was begun in December 1942 on the Ordnance QF 75 mm (a development of the 6-pounder that fired US ammunition) for fitting to British tanks. Mark IV Cromwells were delivered with 75 mm guns from November 1943. To maintain the capability to take on Axis tanks, production was to be split: Noting the problems with the medium velocity 75 mm dual purpose weapon, Vickers had already commenced development of a high velocity 75 mm gun that would fire American 75 mm ammunition but at a much higher velocity. While Cromwell  development had been underway, Soviet forces rejected the US Sherman tank that was to be provided through the third protocol of lend-lease. This led to a surplus in Sherman tank manufacturing capacity, and significant pressure was placed for the Cromwell programme to be cancelled in favour of US-produced Shermans. This would otherwise see a significant proportion of Sherman tank assembly lines closing. A complete move to Sherman tanks was not acceptable to British forces who would then be dependent on the US for tank production. At the same time, Cromwell with the Meteor engine and a HV weapon  was shown to have superior power "and" armament, while US efforts to produce the Sherman replacement, the T20 Medium Tank, were not receiving sufficient attention. The impact of ceasing tank manufacture in Britain would keenly be felt by workers and the war economy at home. A compromise was achieved with a reduction in British tank production during 1943 and 1944, with an increase in consumption of Sherman tanks, the remainder being delivered in parts as spares. Centaur production bore the brunt of this reduction, having only been continued to maintain factories producing Cromwell hulls while the number of Meteor engines  was inadequate. It had already been arranged that Centaur production would be phased out when Meteor engine production increased. The list of machine tools required for the increase in Meteor output was also agreed, allowing Cromwell manufacture to scale. At the same time as negotiations with the US, problems were being encountered with the use of the Vickers 75 mm HV gun in the Cromwell, with a larger turret ring being required. This was now expected to be introduced in mid 1944, leaving the majority of Cromwells with the medium velocity gun similar to the Sherman. Design of the high  velocity variant was split to a separate specification. Intended as just another version of Cromwell, the new A34 version eventually needed significant re-engineering leading to production of the A34 Comet, which used a high velocity gun firing 17-pounder ammunition from a gun by a smaller cartridge down a shorter barrel. In the interim, the A27M version started. Early trials. The first real field test of the design was carried out in August–September 1943, when examples of the Centaur and Cromwell were tested against Shermans (the diesel-engined M4A2 and multibank petrol-engined M4A4) in Exercise Dracula , a long trip around Britain. The Shermans proved to be the most reliable by far, requiring 420 hours of specialist fitter attention over a total distance travelled of with 199 defects. This corresponds to 0.03 hours per mile. In comparison, the Cromwells drove with 367 defects and required 814 hours, or 0.07 hours per mile. The Centaur managed only with 297 defects, due to constant breakdown, and required 742 hours, or 0.087 hours per mile. The Cromwell and Centaur were given additional time to work out these problems. The Cromwell problems were mostly related to oil leaks and brake and  clutch failures, an observer noting that these were well-known and should already have been corrected. The crews expressed their love for the design and especially its speed and handling. The Centaur was largely dismissed, with one observer expressing his hope that units were being equipped with it only for training purposes. The same reviewers unanimously supported the Sherman. A similar test in November demonstrated the Cromwell was improving, while the underpowered Centaur fared no better than in the first test. Alongside Cromwell production, Centaur production design also allowed for the later conversion to the Meteor engine. A small number  were retro-fitted for trials as Cromwell III and Cromwell X. As the Cromwell proved itself, larger numbers were fitted with the Meteor engine on the production line as Cromwell III and IV (not to be confused with the earlier Cromwell III design project). Final specification. The production model design was finalised on 2 February 1944 when Leyland released specifications for what they called the "Battle Cromwell". This included a number of minor changes to the basic design, including of extra armour below the crew compartment, the introduction of an all-round vision cupola for the commander, seam welding all  joints to waterproof and strengthen the tank, and standardising on the A27M version with Meteor engine and Merritt-Brown transmission. The Cromwell Final Specification was applied part way through the production of Cromwell III and IV, changing the appearance and specification of both vehicles. The specification was later improved toward the end of the war with the Cromwell VII, resulting in an upgrade programme. Centaur and Cavalier never met the requirements to enter front-line service. Most were used for training, although a few notable exceptions were used in action. Production. Total A27 production consisted of 4,016 tanks, 950  of which were Centaurs and 3,066 Cromwells. In addition, 375 Centaur hulls were built to be fitted with an anti-aircraft gun turret; only 95 of these were completed. Production was led by Leyland Motors on Centaur, and Birmingham Railway Carriage and Wagon Company on Cromwell. Several other British firms also built Centaur and Cromwell tanks, however, as the numbers required were greater than any one company could deliver. Companies contracted to build the tanks included English Electric, Harland and Wolff, John Fowler & Co., LMS Railway, Metro-Cammell, Morris Motors and Ruston-Bucyrus. Production of Cromwell and Centaur was split  into two different groups. Cromwell was to be built by BRC&W and Metro-Cammell while Centaur was to be built by Leyland, English-Electric, Harland & Wolf, John Fowler & Co., LMS, Morris, Ruston-Bucyrus. Nuffield also switched production to Centaur when Cavalier completed. To increase Cromwell production capacity, English Electric switched from manufacturing Centaur to Cromwell, but remained tooled for Centaur. This resulted in a number of Cromwells being built with Centaur hulls. By January 1943, when production started, Leyland had become the production and design lead for A27 series including subcontractors producing components. Records show that John Fowler & Co. also  produced both varieties. Vauxhall produced two Cromwell pilot models —with a turret similar to that of the Churchill— in the expectation that they would build Cromwells once production of Churchill was terminated in 1943, but Churchill production was extended and Vauxhall withdrew from the Cromwell programme. Design. Hull. The frame was of riveted construction, though welding was used later. The armour plate was then bolted to the frame; large bosses on the outside of the plate were used on the turret. The suspension was of the Christie type, with long helical springs (in tension) angled back to keep the hull  sides low. Of the five road wheels each side, four had shock absorbers. The tracks were driven by sprocketed wheels at the rear and tension adjusted at the front idler, this being standard British practice. Some variants were produced with tracks; later, 15.5-inch tracks were used. As with previous Christie-suspension cruiser tanks, there were no track return rollers, the track being supported instead on the tops of the road wheels, known as the "slack-track" design. The side of the hull was made up of two spaced plates, the suspension units between them, and the outer plate having  cutouts for the movement of the road-wheel axles. The gearbox had five forward and one reverse gears. The first gear was for "confined spaces, on steep inclines or...sharp turns". The transmission was the new Merrit-Brown Z.5, which offered differential steering without clutching or braking, a major advance on previous designs. It gave the Cromwell superb manoeuvrability. The Meteor engine delivered 540 hp at 2,250 rpm giving the Cromwell speed as well as manoeuvrability. This was the maximum rpm, which was limited by governors built into the magnetos. Fuel consumption on "pool" petrol (67 octane) was between 0.5  and 1.5 miles per gallon depending on terrain. The driver sat on the right in the front of the hull, with the hull gunner on the left, separated by a bulkhead. The driver had two periscopes and a visor in the hull front. The visor could be opened fully or a small "gate" in it opened; in the latter case, a thick glass block protected the driver. A bulkhead with access holes separated the driver and hull gunner from the fighting compartment. A further bulkhead separated the fighting compartment from the engine and transmission bay. The engine compartment drew cooling  air in through the top of each side and the roof and exhausted it to the rear. To allow fording through up to deep water, a flap could be moved to cover the lowermost air outlet. Air for the engine could be drawn from the fighting compartment or the exterior; it was then passed through oil bath cleaners. It was modified so that the exhaust fumes were redirected so that they were not drawn into the fighting compartment, a problem found when tanks were drawn up together, preparing to advance. In June 1944, the Cromwell saw action during Operation Overlord , the Allied invasion of Normandy. It had a mixed reception by crews, being faster, with a lower profile and thicker frontal armour plate than the Sherman tank, but also being smaller and more cramped. Cromwell had of frontal armour compared with on the glacis of the early Shermans, though it was unsloped and hence less effective in head-on combat. On later Cromwells this was further increased, first to , then to . Turret and armament. Following British tank doctrine of the time, the vehicle was designed to fire on the move. The turret offered hydraulically powered turret traverse motors with proportional  speed control. Later vehicles fitted an all-round view cupola for the commander to identify and track targets. Both gunner and commander had rotating and pivoting Vickers Gundlach tank periscopes, while fixed episcopes were fitted in the cupola. There was a 7.92 mm Besa machine gun mounted co-axially to the main armament, operated by the gunner. A second was gimbal mounted in the front of the hull, with 45 degrees horizontal and 25 degrees vertical movement. Sighting was by a No. 35 telescope, which was connected through a linkage to the mounting. In the top of the turret was  a 2-inch "bombthrower" angled to fire forward. Thirty smoke grenades were carried for it. Early models of the Cromwell were equipped with the QF 6-pounder (57 mm). Using the new armour-piercing discarding sabot round, which became available in quantity in early 1944, this gun could penetrate over 100 mm of steel armour at ranges on the order of , making it effective against all but the most heavily armoured tanks. However, British tankers had long complained about this weapon's lack of a useful high explosive (HE) round for attacking soft targets like trucks, anti-tank guns and  infantry defences. A HE shell had been introduced for the 6-pounder, but it was described as being largely useless—the calibre of the gun was simply too small to carry a useful load of explosive. This was not entirely accidental; British tank policy of the time suggested that different models of the same tank, carrying different specialised weapons, was a better solution to this problem than a single weapon that attempted to do all things. Experience with the US M3 75 mm gun suggested this thinking was wrong, that a single gun could be used in a "dual purpose