FV4005 was a British Cold War prototype tank that had the largest gun ever fitted to a tank. A fearsome weapon that was superfluous as soon as it was developed, it nevertheless was the apex of the race to build ever bigger tanks with thicker armour and increasingly powerful guns.

Development: British Tank Development Before FV4005

Britain had invented the tank as a trench breakthrough weapon during the First World War, and had continued to lead the world in tank development and theory throughout the 1920s, only for investment in the army to plummet during much of the 1930s.

At the outbreak of the Second World War, British tanks had three different overall purposes:

• Light tanks - except for some reconnaissance use soon proved obsolete.
• Cruiser tanks - were highly mobile but thinly armoured, intended to charge through enemy lines and cause maximum mayhem and disruption as quickly as possible.
• Infantry tanks - slow, heavily armoured tank that provided infantry support.

At the outbreak of war some of these tanks were extremely capable vehicles, particularly infantry tank Matilda II. During the war tank development proceeded at an incredible pace; effectively a new generation of tanks superior to those that came before were created every year. When France fell and the British army was evacuated from Dunkirk, virtually all of Britain's tanks had been abandoned. The decision was made that in order to make up for this, rather than concentrate on tank development which would result in improved tanks at a later date, Britain would instead make as many existing tank models as possible as soon as possible to replenish lost numbers, and only then restart development. This essentially meant that for the rest of the war, Britain's tank development was a year behind that of Germany and other nations.

It should be said that there were also two other key reasons for British tank's poor performance: transport logistics and engine size. In the years leading up to the Second World War there was a high tax on road vehicles with large engine sizes. This killed demand for powerful engines, meaning Britain's motor industry had no experience or capacity in making them when large, powerful engines were needed to power tanks. This meant that for much of the war, Britain's tanks were underpowered, resulting in them either being very slow, or if mobile, lightly armoured.

The logistic issue was that the more powerful a tank's gun is, the larger it is. The larger the gun, the larger the turret needed to fit it, and the larger the turret ring needed to attach the turret to the tank's hull. If a tank is going to be transported by rail, the turret ring width is limited, which in turn limits the size of the gun that the tank can use. Also, the more powerful and armoured a tank, the heavier it is. Britain is an island and for a tank to be used in combat, it needs to be shipped, with most dockside cranes limited to carrying no more than 30 tons. With both weight and size limited, British tanks were constrained in ways that German and Russian tanks were not.

The experience of being forced to fight the war with poorly performing tanks led the British army to resolve that in any potential upcoming war, Britain would have the best tanks in the world.

A New Threat

When Germany was defeated at the end of the Second World War in Europe, the Soviet Union displayed their latest tank in the Allied Berlin Victory Parade on 7th September 1945 in for the first time, unveiling the IS-3¹ heavy tank to the world. The IS-3's design, bigger, more heavily armoured and more powerful than any Western tank, was a shock to the British military. They concluded that they quickly needed to upgrade, and especially upgun, their own tanks to deal not only with this existing Soviet heavy tank, but any potential Soviet successor vehicles - which in theory would be built with even thicker armour.

Talking Cents

At the war's end, Britain's new tank was the Centurion. This had been designed in 1943 as a tank that would, from the outset, be capable of carrying Britain's highly-effective 17-pounder gun, and thus be able to meet any other Second World War tank on an equal footing. Improved lorry logistics during the war meant that it was becoming possible to transport tanks by road, and that the tank's performance would not need to be limited to the width and weight requirements. With the war raging, priority remained producing the existing tank types and spares for repairs in the required numbers to outproduce the Axis powers, which meant that when the Second World War ended only a few prototypes had been produced, with these on their way to Germany in May 1945 just as the war ended. This tank was originally designed to be a cruiser tank, mobile and armed with the most powerful Allied anti-tank gun, but as it was powered with a Rolls Royce Meteor engine, derived from the famous Merlin aircraft engine, it was powerful enough to allow it to have the heavy armour of an Infantry tank. It was therefore considered to be a Heavy Cruiser tank.

As the cruiser tank concept had largely been a failure during the Second World War, the Centurion - affectionately nicknamed the 'Cent' by its crews - was also unfairly considered to be an inevitable failure by the General Staff, who began planning its replacement.

Son of a Gun?

With the Iron Curtain descending, and tensions between the USSR and the West rising, work in Britain began on designing a new generation of tanks. These would be bigger, stronger and even more heavily armed. While the Centurion was potentially a match for the IS-3, Britain believed that the Soviets were starting an arms race, and they would need a tank to deal with a more powerful replacement. This would need a gun capable of destroying heavily armoured tanks at a range beyond which any upcoming Soviet tank heavy tank could return fire and mount it in a new chassis. The Royal Ordnance developed such a weapon, the L4A1 183mm calibre gun, which weighed 2.8 tons but was capable of firing a projectile at 2,350 feet per second that would smash through 6-inches (152mm) of armour plate at 60° at 2,000 yards. It was believed any hit from the gun would immediately disable any enemy tank even if it was not outright destroying it. The ammunition it fired were HESH (High Explosive Squash Head) rounds, which weighed up to 72lb - about the weight of a washing machine - and 30 inches (76cm) long. The ammunition was two piece, so after the explosive round an additional propellant case weighing an additional 68lb and further 68cm long. Together the round was 1.5 metres tall.

In November 1950 two stages of prototypes were ordered. These would determine whether it was possible and/or desirable to ultimately up-gun Britain's Conqueror heavy tank then in development, which was designed to carry a 120mm gun. However as Conqueror was not ready, as an interim measure, prototypes were developed in which the new, giant gun would be mounted on an existing Centurion chassis for initial gunnery trials. This would mean by the time the Conqueror was ready, it should be possible to simply mount the new gun on the new tank as the trials and development process would have already been complete and any issues with the new gun addressed.

FV4005

A Centurion Mark III hull was chosen to use for the tests, as these were readily-available and reliable. The name FV4005 means Fighting Vehicle, the number 4000 referred to the Centurion and this would be the fifth variation of the Centurion².

All The World's A Stage

The first, basic prototype was to see whether it was possible to put an open-mounted gun this size on a tank hull and identify issues. Work began in early 1951 and completed in April 1952. Stage 1 was equipped with an autoloader that held five rounds to assist with the weight. It showed that because of the 87-tonnes of recoil force, it was only possible to fire the gun within a limited arc of 45° at the front of the tank. As well as a concentric recoil system around the barrel's breech, a recoil spade or ground anchor, which looked like a bulldozer blade, would be winched down from the back before firing to dig into the ground to help combat the blast force.

For a tank weapon, the gun barrel was phenomenally long. With firearms, the longer the barrel is, the more accurate the projectile, which is why a rifle is always more accurate than a pistol even if firing identical ammunition. As the gun was intended to be accurate over vast ranges, the barrel needed to be long, however increased barrel length also has issues. The longer the barrel, the heavier it is and therefore the more likely it is that the weight might lead to minute warping or bending, thus affecting accuracy. A long barrel can also potentially affect the vehicle's mobility when traversing trenches or ditches, with tanks with long barrels being known to become embedded in the ground. To mitigate these issues, a barrel cradle was fitted to the vehicle for the barrel to rest in when not in use.

Trials finished by June 1953, with the report stating that when firing without the recoil spade, the front of the 50-ton tank would lift up by 17 inches and back drop by 10 inches and would be pushed back 10 inches. If fired at 90° the whole tank would be pushed back 2 inches sideways. Repeated firing also bent and sheared internal components - essentially firing the main gun caused the tank to shake itself apart.

This led to the Stage 2 of the FV4005, which had the gun encased in a fully-enclosed turret, though the turret was unarmoured, only 14mm thick to keep the tank under 50 tons, and while capable of keeping out heavy rain and hail, offered no protection from enemy forces. It did mean there was no room for the autoloader in the turret, so loading the gun required two loaders.

The Stage 2 went through extensive trials through 1955 and 1956. A better recoil system was developed in addition to the recoil spade, as Stage 1 trials had shown the recoil was still so powerful that the tank was shaking itself apart. Trials in 1955 were satisfactory. The gun's hitting power was huge, but with the projectile's low velocity meant it was susceptible to crosswind affecting accuracy, and it was only capable of firing two rounds a minute, and with only 12 rounds carried on the tank, the decision was taken in 1957 to cancel the project.

During the early 1950s, Britain and other nations around the world developed anti-tank guided missiles, which were able to do the same job at a fraction of the cost, weight and be mounted in much smaller, more manoeuvrable vehicles or even be carried by infantry. There was no longer a need to develop a major weapons platform when a man with a missile could do exactly the same thing but cheaper and more effectively. Meanwhile, Stalin, the biggest supporter of the heavy tank, had died in 1953; his replacement Nikita Khrushchev ordered the end of heavy tank development.

Similarly, advances in technology made smaller guns and new forms of ammunition more effective. The FV4005 Centurion hull was re-purposed and the Stage 2 turret and gun was sent to the Royal Military College of Science in Shrivenham.

Preservation and Restoration

In 1971 the Tank Museum acquired the turret and gun and left it outside the museum to be climbed on by visiting children. In 2007 the turret was mounted on a spare Centurion Mark XII chassis to be used as a gate guardian. In 2023 Joe Hughes led a project to restore the turret with an accurate, running Centurion mark III chassis, using or recreating all the original components³. It was intended to restore the vehicle in time for it to run at Tankfest 2024. An appeal was launched on the Tank Museum's website and within 24 hours, all the funds needed had been raised.