The FV4005 has what is almost certainly the largest gun ever fitted to a tank. It marks the high point of the race throughout the history of armoured warfare to build bigger and bigger guns that could defeat thicker and thicker armour at longer and longer range. After this point, the advent of guided missiles and more advanced gun ammunition would allow this improvement to continue, but at far lower size and weight.
The vehicle itself originated in the late 1940s. The British Army realised they needed to reliably destroy new Soviet heavy tanks such as the IS-3 and its potential successors well beyond the range that they could return fire, but they had no gun that could hope to do this. They began a project to develop one.
The intention was to mount the resulting weapon on a new, purpose designed vehicle, the Heavy Gun Tank Number 2, or FV215 (some sources call it Heavy Anti Tank Gun SP No.2). There were concerns that the nascent Cold War could turn hot before it was ready in numbers, so a stop gap solution was also to be developed using the in-production Centurion tank hull. This was named Heavy Gun Tank Number 1, or FV4005.
The 183mm Gun L4A1
The requirement for the new gun was to defeat 152mm (6 inches) of armour plate sloped at 60° at 2000 yards. This was beyond any existing gun. The intention was that the round should be powerful enough to disable or ‘disrupt’ a vehicle through any kind of hit, even if it was not physically destroyed. The gun was named the L4A1, and the calibre settled on was 183mm, or 7.2”. It would fire High Explosive Squash Head (HESH) ammunition.
This ammunition was incredibly large and heavy and had to be loaded as a separate projectile and case. The projectile weighed 145lb (65.8kg) and was 29 ¾” (76cm) long. The case, containing the propellant, added 67.75lb (30.7kg) and 26.85” (68cm). It had a muzzle velocity of 2500fps (762m/s).
This requirement for FV4005 was issued in November 1950 and was to be fulfilled in two stages. Stage 1 was described as ‘experimental only, intended to prove the suitability of this type of vehicle as a firing platform and to solve problems connected with the handling of heavy ammunition.’ ‘A small production’ was then planned of Stage 2 vehicles for service use. One Stage 1 and two Stage 2 turrets were ordered from Vickers to be fitted to three Centurion Mark 3 hulls supplied by the Army.
FV4005 Stage 1
The gun mounting fitted to the Stage 1 vehicle could traverse through 360°, but the recoil force meant that firing was only safely possible within a limited arc to the front. According to surviving blueprints, the gun could elevate and depress between -5° and +10°. A load-assist system was fitted, which lined up projectiles and charge for the loader to then ram into the breech. It was fitted with a concentric recoil system around the breech end of the barrel, which required less space than a conventional recoil system.
The hulls on both Stages were fitted with a tripod gun crutch on the front glacis plate which supported the barrel at 2° of elevation when the vehicle was in motion, and a recoil spade, similar in appearance to a dozer blade, on the lower rear. This would be lowered and dig into the ground before firing, helping reduce the proportion of the 87 tonnes of recoil force that acted on the vehicle and its components every time the gun was fired.
FV4005 Stage 2
The Stage 2 vehicles were more representative of the final production configuration of the FV4005. The most obvious change was the fully enclosed turret, protected by a 14mm thick shell, but the gun mounting inside also had some significant differences. It had the same range of motion as Stage 1, but the load-assist system was removed. Instead, a second loader was added to the crew, with each dedicated to loading either projectile or case.
There was space for 12 rounds internally, along with a rail and winch system on the engine deck to allow for speedy reloading from a truck parked behind the vehicle.
Firing trials were conducted in 1955. 150 rounds were fired with ‘satisfactory’ results, although it had the same firing arc restrictions as Stage 1. The concentric recoil system on Stage 1 had suffered some faults during its firing trials. Stage 2 used conventional hydropneumatic recoil cylinders mounted above the gun instead, and this proved much more reliable.
The project was cancelled in August 1957, along with FV215. Although the gun’s hitting power was enormous, due to the large size and relatively low velocity of the projectiles, they were susceptible to crosswinds. This reduced the gun’s practical accuracy at its maximum effective range of 2000m to an unacceptable level. The rate of fire was also too low, at just 2 rounds per minute.
The decision was made that future long range anti-tank capability was to be provided by missiles. The first of these to enter service, Malkara, had one third the weight of a warhead and half the velocity of a 183mm round, but twice the effective range and far greater accuracy. In addition, it could be fired from a small, light wheeled vehicle.
The three Centurion hulls were returned to the Army, and the turrets were distributed to experimental establishments. The Tank Museum’s Stage 2 turret came here in 1970 from the Royal Military College of Science.
In 2007, it was mounted on a representative Mark 12 Centurion hull and placed on display at the Museum exit.