The Cromwell tank

How the jumping tank came about

Discussions about World War II tanks are usually dominated by comparisons of the American Sherman and the German Tiger or the Panther. Less popular tanks such as the British Churchill and the Cromwell don’t get as much attention, even though they are just as interesting. In today’s article we take a closer look at the Cromwell and try to shed some light on its significance.

The Cromwell tank, officially Tank, Cruiser, Mk VIII, Cromwell A27M, was designed to address the British Army's need for a faster and more mobile tank that could keep up with their infantry units. Based on their experiences of World War I and training exercises in the interwar period, British military theorists believed that the future of armored warfare required armor to be broken up into different roles. The infantry needed a slower, more heavily armored tank, the “infantry tank,” for protection, while a new, fast-moving type of “cruiser tank” was also necessary. The new tank was supposed to take the role of cavalry: it was to be used for breaking through enemy lines and to exploit the breakthrough by pursuing and surrounding the enemy. This new type of armor even used the same terminology as the cavalry; for example, exiting the tank was called “dismounting,” and the surviving crewmen of a destroyed tank were referred to as “dishorsed” or “unhorsed.”

True to this principle, the Cromwell was faster and more agile than British infantry tanks such as the Valentine and the Churchill, but it had lighter armor and a less powerful gun compared to heavier tanks like the German Tiger and Panther. The latter two were more mechanically complex, which made them harder to maintain in the field, whereas the Cromwell was easier to repair and had fewer mechanical problems - though it still fell behind the Sherman in that regard. In comparison with the Sherman, its closest match in the American arsenal, the Cromwell had better mobility, but the Sherman was more heavily armed and armored.

Nuffield started developing the Cromwell I, which eventually saw service in relatively low numbers as an interim solution under the name A24 Cavalier, with the old Liberty engine and using many parts from the Crusader. Although the design was new and up to date, the old engine was too weak for the heavy armor of the Cromwell I, and the vehicle was generally underwhelming.
 
The next stage of development was the A27L Cromwell II, which became the Centaur. It was a transition between the Cavalier and the eventual, definitive version of the Cromwell, with almost every component but the engine in common with the latter. The power of the Liberty engine still wasn’t enough to run the tank as expected. By this time, production was transferred to the Leyland Factory, which previously also submitted a design for the tender together with Birmingham Railway Carriage & Wagon.

Unbeknownst to the developers, Rolls-Royce was already at work creating a new, redesigned version of the Merlin fighter engine, made for non-aerial use. The Merlin engine was used in the Spitfire, the legendary interceptor that was crucial to saving the United Kingdom during the Battle of Britain in the summer of 1940. Rolls-Royce was known for the quality and reliability of its engines, and the Merlin was no exception. With its raw power, high degree of reliability, and compact and lightweight design, the Merlin engine was suitable for use in tanks, although it needed to be heavily adapted for the job. The tank-based version of the Merlin, the Meteor, was a V12 water-cooled gasoline engine. The tank design did not require the raw horsepower of the Merlin engine, so the Meteor’s output power was reduced to around 557–660 hp. This meant that the new motor could run on lower-octane petrol; it was also made more reliable through the use of cast pistons as opposed to the forged ones in the Merlin.

Let’s take a look at the structure of the tank. The frame of the Cromwell’s hull was made of riveted beams, with the armor plates bolted to them. Later versions used welding; the weight saved by this construction method allowed the armor to be thickened by 30 mm. Welding also improved armor integrity, since welded plates have fewer weak points than bolted-on or riveted armor. The latter two are likely to take heavy damage if the bolted or riveted areas are hit.
 
The suspension was of the Christie type. It was named after its inventor, American engineer J. Walter Christie, and used long helical springs angled back to keep the hull low. The five road wheels on the vehicle each had four shock absorbers, which made the vehicle easy to drive on uneven terrain and allowed a higher top speed.

True to a British vehicle, the driver sat in the right side of the driver’s compartment, rather than the left usual in most countries. The driver and the hull gunners next to him were separated from each other by bulkhead, and both of them were separated from the fighting compartment behind them by another one, an arrangement that was far from common. The tank’s mobility was enhanced by a transmission that allowed the driver to move the two tracks at different speeds without using steering clutches or breaks. While the Cromwell was faster and had a lower profile than the taller-than-average Sherman, it was also more cramped, with 64 mm of frontal armor compared to 51 mm on the glacis of early Shermans. (It should be noted that the Shermans’ armor was sloped, which increased the effective armor thickness and therefore deflected the projectiles more effectively.) 123 Cromwells were later produced with additional armor on the front hull, which increased its protection to 101 mm. The Cromwell was also equipped with a little charging engine nicknamed “Tiny Tim,” which was used to charge the radio with the push of a button even when the main engine was off.

The turret was of a hexagonal shape and was made of cast-hardened steel with a thickness of 76 mm at the front and 50 mm at the sides, making its armor 25 mm thicker both on the front and the sides than the one on the Panzer IV. The gunner operated both the main gun and a 7.92 mm Besa machine gun, and had his own periscope and main visor. Initially, the Cromwell was equipped with the QF 6-pounder gun, which was effective against tanks, but couldn’t do serious damage to soft targets like unarmored vehicles or groups of infantry. It was soon swapped for the ROQF (Royal Ordnance Quick-Firing) 75 mm gun which could fire both American and French-made ammunition. This gun was more versatile; it was able to fire high-explosive shells for attacking soft targets and also armor-piercing rounds against armored targets. Changing the gun was rather easy since both the 6-pounders and the new ones used the same mounting.

The Cromwell was designed to fire on the move, with hydraulic turret traverse motors and proportional speed control for better handling over acceleration. The commander had an all-round view cupola and gunner and commander both had rotating Vickers Gundlach tank periscopes. The turret also had a 2-inch "bombthrower" for firing forward-angled smoke grenades. While the high-explosive shells were useful against unarmored targets, the new ROQF 75 mm was not as effective against armored targets as its predecessor, the 6-pounder. Nevertheless, its improved versatility made the ROQF 75 mm the standard weapon on the Cromwell throughout the war.
 
The tank was initially kept on British soil for training purposes until the Normandy landings in June 1944, where it saw its first action. The Cromwell was primarily used in the armored brigades of the 7th “Desert Rats" Armoured Division and the armored reconnaissance regiments of the Guards Armoured Division and the 11th Armoured Division. The Cromwell was also used by the 1st Polish Armoured Division and the 1st Czechoslovak Armoured Brigade.

During the Battle of Normandy, the Cromwell struggled and suffered high losses in the narrow lanes and thick hedgerows of the local bocage country, where it couldn’t bring its mobility to bear against prepared German ambush position. However, the tank's mobility and speed proved to be its strengths once the terrain became more favorable after the breakout from Normandy and during the rapid push across France. One of the most impressive showcases of its “talents” occurred during Operation Market Garden. A squadron of Cromwells crossed a bridge over a canal and went over a hedge where they were ambushed by four German 88 mm flak guns. These fearsome weapons could easily put a shell through a Cromwell. Now under enemy fire, the Brits wheeled around in a semi-circle, trying to avoid the attack of the 88s while finding their way back over the hedge to the bridge. When going over the hedge back again they realized that the bridge was hundreds of yards away now. The only way back would be in front of the enemy lines; that meant suicide, so they decided on a daring action: making use of the high speed of the 28-ton tank, they tried to jump over the canal.

The first tank driver was very skilled and stepped on the clutch while mid-air to let the motor run freely, letting him hit the ground running. After landing and re-attaching the clutch, he was in gear again and could roar off to a safe distance. The driver of the second tank was not so smart: he forgot to press the clutch mid-air, and landed with the gears still in contact with the engine. The impact made the gears scream, and the motor couldn’t keep the tank running. However, the tank was still being carried forward by its momentum, so the vehicle stood up on its nose and catapulted forward everything it had in the back compartment, including spare parts and fuel cans. Luckily, the momentum had stopped there and the tank landed back on its tracks and could roll on to follow the first one. The third tank was slower than the other two. The crew was afraid they might not make the jump, but it still seemed like the best idea in the moment. They revved the engine and accelerated as much as they could, but still didn’t have enough speed to take them all the way through the canal. They landed on the very edge. It took them a few moments to climb up the bank and rush after the other two. The crews later went back to measure the canal and found out that they had jumped over 20 feet (6 meters) of water.

The tank was praised for its speed and reliability, and had a low profile that made it difficult to spot. The standard 75mm gun was effective against most German armored vehicles but was unable to penetrate the frontal armor of heavier tanks like the Tiger and Panther. A new turret was designed for the Cromwell chassis that could house the powerful QF 17-pounder gun that was also carried by the Sherman Firefly (Read our earlier article – The M4 Sherman). This new design led to the A30 Challenger tank, which was produced in low numbers and much too late in the war to make a significant impact.

Most of the Cromwells were used up in the war or were sold for scrap. Some of the remaining ones were used by Israeli forces in the 1948 Arab-Israeli War, while others were deployed in the Korean War by the British, where all were captured or destroyed. Several Cromwells are on display throughout the world today, showcasing the tank's historical significance. You can see them even on our tours visiting the Tank Museum in Bovington, the Pegasus Bridge Memorial in Normandy or in the Bastogne Barracks in Belgium.

The Cromwell was eventually replaced by the Centurion. The latter “inherited” the Meteor engine, but was otherwise redesigned to be an all-around tank that could fill the role of any other tank in the army.  Newer technology meant that the new vehicle could be as fast as a light tank, have the firepower of a super-heavy tank and the armor of a heavy tank, while still only weighing as much a medium. This new concept was called “universal tank or main battle tank” (MBT) and is still followed in tank design today. The Centurion’s development finished just after World War II ended, and it became one of the most successful tanks ever designed, with some of its derivatives still in service today. With such a fundamental shift in tank design after the war, one might say that the Cromwell was the last cruiser tank to see significant service.

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