The Cromwell Cruiser Tank (A27M), and the related Centaur (A27L) tank, were one of the most successful series of cruiser tanks fielded by Britain in the Second World War.
The Cromwell tank, named after the English Civil War leader Oliver Cromwell, was the first tank put into service by the British to combine a dual-purpose gun, high speed from the powerful and reliable Meteor engine, and reasonable armour, in a balanced package. Its design formed the basis of the Comet tank.
The Cromwell and Centaur differed in the engine used. While the Centaur had the Liberty engine of the predecessor cruiser tank, the Crusader (and the interim A24 Cavalier), the Cromwell had the significantly more powerful Meteor.
Apart from the engine and associated transmission differences, the two tanks were the same and many Centaurs built were fitted with the Meteor to make them Cromwells.
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, within the 7th, 11th and Guards Armoured Divisions.
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 Cromwell tanks. The Centaurs were not used in combat except for those fitted with a 95mm howitzer, which were used in support of the Royal Marines during the invasion of Normandy.
Development – Initial designs
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 the new tank to replace it. The tank was to be fitted with the QF 6 pounder gun and was expected to enter service in 1942.
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 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and powered by its version of the Liberty engine, a V-12 design dating the late days of World War I and now thoroughly outdated.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 I 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 entirely underpowered and 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.
With the start of the war, Rolls-Royce ended car production and set up a design team looking for other ways to use their production capacity. The team formed under the direction of Roy Robotham at Clan Foundry near Belper, north of Derby.
In October 1940 Robotham met with Henry Spurrier of Leyland Motors to discuss British tank design. They decided to attempt to fit a Rolls-Royce Merlin engine to a Leyland tank for testing. They removed the turbosupercharger from a Merlin Mk. III and fit it 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 50mph.
Everyone was so impressed by this display that Leyland arranged to start production of 1,000 examples of the engine as the Meteor. They planned to fit this to BRC&W-built versions of their original A24 submission. However, in mid-1941 Leyland changed its mind, concerned about cooling problems. They instead suggested using a diesel engine of their own design, although this would produce only 350 horsepower (260 kW) compared to over 500 from the Rolls design.
The Tank Board then placed an order directly with Rolls for the Meteor. The resulting design was ordered as the A27. When Leyland suggested that the take be designed to fit either the Meteor or the Liberty, the two versions were given the numbers A27M and A27L, respectively, and the names Cromwell III and Cromwell II. The diesel concept was abandoned.
The first prototype of Meteor powered Cromwell II was delivered in January 1942, several months before the A24 that was supposed to precede it. With nearly 600 hp (450 kW) it proved to be exceptionally mobile when tested. Orders were placed for both versions, as there were concerns about the production rate of the Meteor.
Even when assigned reduced production quotas, BRC&W proved unable to meet demand, and Leyland eventually took over production of both versions.
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, who had met Whittle and was fascinated by the jet engine. 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. The official handover took place on 1 January 1943. 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 Centaur production design allowed for the later conversion to the Meteor engine and many Centaurs were converted to Cromwells before use.
The first real field test of the design was carried out in August 1943, when the Centaur, Cromwell, Sherman M4A2 and Sherman M4A4 were all tested in Exercise Dracula, a 2,300 mile long trip around Britain.
The Sherman’s proved to be the most reliable, by far, while the Centaur proved a complete failure, often arriving at its checkpoints hours later with the sun long gone down. The Cromwell proved better than the Centaur but not up to the standards of the Shermans, so the team was given additional time to work out the problems. A similar test in November demonstrated the Cromwell was improving, while the underpowered Centaur faired no better than the first test.
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 6 millimetres of extra armour below the crew compartment, seam welding all the joints to waterproof the tank, and standardising on the Meteor engine and Merritt Brown transmission.
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. Several British firms besides Leyland contributed to production of the Cromwell and Centaur, including LMS Railway, Morris Motors, Metro-Cammell, Birmingham Railway Carriage and Wagon Company and English Electric. Some variants were produced with 14-inch-wide (360 mm) tracks; later, 15.5-inch tracks were used.
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.
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. 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 Meteor engine delivered 540 hp at 2,250 rpm. 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, separated from the hull gunner 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 4 ft 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.
The Cromwell had revisions to make before service, changing from the QF 6-pounder to the ROQF 75 mm gun, which was an adaptation of the 6-pounder design to fire the ammunition of the US M3 75 mm gun, which gave it a better HE round to use in infantry support.
This meant that the 75 mm used the same mounting as the 6 pounder. 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 than the Sherman tank and thicker frontal armour plate 3 in as against the 2 in (51 mm) on the glacis of the early Shermans, though it was unsloped and hence less effective. On later Cromwells this was increased, first to 3 1⁄4 in, then to 4 in. The 75 mm gun, though able to fire a useful HE shell, was not as effective against armour as the 6-pounder or the Ordnance QF 17 pounder gun.
A derivative of Cromwell, the Cruiser Mk VIII Challenger, was built to take the 17-pounder but only a small number were built. Most 17-pounder armed tanks to see service in the war were the Sherman Firefly variant of the Sherman.
There was a 7.92mm 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. The mounting gave 45 degrees of coverage to the front (it had 25 degrees of vertical movement as well) and 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 “bomb-thrower” angled to fire forward and thirty smoke grenades were carried for it.
The Cromwell was the fastest British tank to serve in the Second World War with a top (ungoverned) speed of 40 mph (64 km/h). However, this speed proved too much for even the Christie suspension and the engine was governed to give a top speed of 32 mph (51 km/h), which was still fast for its time. Thanks to its excellent engine power and Christie parentage the Cromwell was very agile on the battlefield.
The dual purpose 75 mm main gun fired the same ammunition as the US 75 mm gun and therefore it had around the same HE and armour-piercing capabilities as the 75mm equipped Sherman tank. The armour on the Cromwell ranged from 8mm up to 76mm thick overall. However, on all-welded vehicles built by BRCW Co. Ltd, the weight saved by the welding allowed for the fitting of appliqué armoured plates on the nose, vertical drivers’ plate and turret front, increasing the maximum thickness to 102 mm.
These vehicles are identified by their War Department numbers carrying the suffix W, e.g. T121710W. This armour compared well with that of the Sherman, although the Cromwell did not share the Sherman’s sloped glacis plate. The Cromwell crews in North-West Europe succeeded in outflanking the heavier and more sluggish German tanks with superior speed, manoeuvrability and reliability.
However, the Cromwell was still not a match for the best German armour and British tank design would go through another stage, the interim Comet tank, before going ahead in the tank development race with the Centurion tank.
The Centaur was chiefly used for training; only those in specialist roles saw action. The Close Support version of the Centaur with a 95 mm howitzer, saw service in small numbers as part of the Royal Marine Armoured Support Group on D-Day and a number were used as the chassis for combat engineering vehicles such as an armoured bulldozer.
The Sherman remained the most common tank in British and Commonwealth armoured units. Cromwells were used as the main tank in the armoured brigades of only the 7th Armoured Division, although the Cromwell was used in the armoured reconnaissance regiments of the other British armoured divisions (Guards Armoured Division and 11th Armoured Division) in North-west Europe, because of its speed and relatively low profile.
The Cromwell in turn was succeeded by small numbers of the Comet tank, which was similar to the Cromwell, being based on it and shared some components but had a superior gun in the 77 mm gun (a version of the 17 pounder with different ammunition).
The Cromwell was found to be very reliable with excellent speed and manoeuvrability, though it required more maintenance than the Sherman. 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 northern Europe, the Cromwell was used by Allied units of the 1st Polish Armoured Division (10th Mounted Rifle Regiment) and 1st Czechoslovak Armoured Brigade. After the war, the Cromwell remained in British service, and saw service in the Korean War with 7 RTR and the 8th King’s Royal Irish Hussars.
The Cromwell / Centaur had the distinction of being the first tank to go into service with the Greek Army during the re-formation following the Second World War.
Fifty-two Centaur I tanks were donated early in 1946, during the opening stages of the Greek Civil War but they were kept in storage due to the lack of trained personnel. In 1947, the first Greek officers returned from training courses in the United Kingdom and training of tank crews began.
The Centaur saw limited service in the civil war as in 1949 battles were fought on mountains. Centaurs formed the core of the Greek Armour Corps during the 1950s and were retired in 1962, having been replaced by US-built M47s. Finland used the Charioteer version of the Cromwell post war.