The FV4005 "Doombarn"
The development of the L4 started in 1950, and was aimed at increasing the firepower of the ‘Heavy Gun Tanks’. This was a uniquely British designation that was not governed by tank weight, but the size of the gun. A requirement was formulated for a tank armed with a gun capable of defeating a 60-degree sloped plate, 6 inches (152 mm) thick, at up to 2,000 yards (1,830 meters), a feat impossible even for the powerful 120 mm L1 gun of the FV214 Conqueror. By 1950, Major General Stuart B. Rawlins, Director General of Artillery (D.G. of A.) had concluded that there was no gun available with that level of ballistic performance and an investigation was launched. Initially, the British Military looked at the development of a 155 mm gun that would be standardized with the USA. However, even this lacked the required punch and, as such, 6.5 and 7.2 inch (165 and 183 mm respectively) High-Explosive Squash Head (HESH) shells were looked at.
It was not until December 1952 that the designation of the gun was officially updated to 183 mm. The design of the gun was accepted and was serialized as the ‘Ordnance, Quick-Firing, 183 mm, Tank, L4 Gun’. In reality, only the HESH shell underwent further development and the number of charges was dropped to one. The 183 mm L4 became one of the largest and most powerful tank guns in the world.
The design of the vehicle would be held in limbo, ready to go into production if necessary. This stopgap vehicle would be based on the Centurion of the FV4000 series, with the original turret removed. The vehicle would go through two ‘Stages’ or ‘Schemes’. ‘Stage 1’ was built to test the gun and its mount on the Centurion chassis. The ‘Stage 2’ was a finalized design and would be the production standard. The vehicle was given the designation of ‘Heavy Anti-Tank, SP, No. 1’ – ‘SP’ standing for ‘Self-Propelled’. Officially, the FV4005 was never given the traditional British ‘C’ name such as the FV4101 Charioteer and FV4004 Conway before it.
In total three prototypes were ordered – a single Stage 1, and two Stage 2s. The FV4005 would fill the role of a ‘Heavy Gun Tank’. As such, the vehicle would engage targets from long-range, firing over the heads of attacking lighter tanks.
The Centurion was chosen as the basis for this vehicle and three Mk.3 hulls were removed from service for the prototype development. Other than the removal of the turret and various small additions, the hull would remain mostly unaltered. Armor on the hull remained the same thickness, with about 3 inches (76 mm) at roughly 60 degrees on the front slope. A 650 hp Rolls-Royce Meteor petrol engine, located at the rear of the vehicle, propelled the tank. The Centurion used a Horstmann style suspension, with 3 bogies per side carrying 2 wheels each. The drive sprocket was at the rear with the idler at the front. The driver was located at the front right of the hull.
The Stage 2 was built closest to what a production version of the FV4005 would consist of. As such, a number of changes were made between the two Stages. The biggest change was the design and construction of a fully enclosed turret to the form of little more than a large box. The loading assist for the loader was also deleted, and the concentric recoil system was replaced by a hydropneumatic type.
The turret was welded and fabricated from ½ inch (14 mm) thick steel and was there to protect the crew from small arms fire and shell splinters. As this was intended to be a second line vehicle that would keep out of the range of enemy AFVs, the FV4005 did not need really thick armor. There were two hatches on the roof and one large door on the rear. The roof hatches were two-piece and, in front of them, were two single periscopes installed in the turret roof.
Like the Stage 1, the Stage 2 featured a recoil spade installed at the rear of the vehicle. However, on the Stage 2, a hand-cranked winch was installed on the rear of the vehicle to lower the spade.
Despite the general success of the project, the FV4005 suffered much the same fate as the FV215. The feared Soviet heavy tanks, like the IS-3, which these vehicles were designed to defeat, were not being made in the massive numbers expected, indicating a shift in policy to lighter, more maneuverable, and more lightly armored tanks. The need for ‘Heavy Gun Tanks’ like the Conqueror, FV215 and the FV4005 stand-in, from this perspective, was simply becoming absent. Other changes were also taking place as technology-wise, larger caliber guns with their huge ammunition were becoming obsolete by improved anti-armor performance of smaller guns and by the appearance of a new generation of accurate Anti-Tank Guided Missiles (ATGM).