Anti-IS QF L4 gun and its variants
In order to meet these requirements, the designers had to find a much more powerful gun than the L1A1. The British didn't bother with the small stuff and went right up to a caliber of 7.2 inches (183 mm). Using such a powerful caliber was no accident. This new gun was based on the 183 mm BL 7.2 inch Howitzer, which dates back to WWI. Initially, the howitzer had a barrel length of 22.4 calibers, but this was extended to 33.1 calibers. Unfortunately, even this extension was not enough to fight Soviet tanks.
In 1950, work started on the QF L4 gun, the most powerful tank gun in the world. The gun weighed a little under 4 tons and had nearly 87 tons of recoil force. In order to clear the fighting compartment of propellant fumes, the gun had a fume extractor fitted. Only one type of shell was planned for this gun: HESH (High Explosive Squashed Head). Not only is the caliber of the L4 stunning, but also the weight of the rounds. The propellant was separate from the shell, but this didn't make the loader's job much easier: the mass of the shell was 72 kg, and the mass of the propellant was 32.8 kg.
On November 9th, 1950, the War Office held a meeting to determine what vehicle this super-powerful gun would be placed on. The meeting resulted in four variants:
- A fully armoured fighting machine (effectively a tank) with a fully rotating turret.
- An SPG with powerful front armour, but a limited traverse angle.
- An SPG with a fully rotating turret, but thin armour.
- An SPG without armour.
Variant 1/2: FV215
The contract to develop the first variant went to Morris and was later transferred to Vickers-Armstrong. The chassis of the heavy FV200 tank was used, with the suspension from the heavy FV214 Conqueror tank. The project had multiple names: Heavy Gun Tank No.2, Heavy Anti-Tank SP No.2, FV215 Heavy Anti-Tank SP No.2 or simply FV215. The index Heavy Gun Tank No.2 was incorrectly interpreted by historians, resulting in a mythical project called FV215B. In reality, all these indices pointed to the same vehicle armed with the 183 mm L4 gun.
This project combined the first and second variants. Theoretically, the turret could rotate fully, but the gun was limited to firing within a 90 degree arc. The turret was placed in the rear in order to prevent the huge barrel from sticking out too far. The ammunition capacity was only 20 shells. The rate of fire of the tank was supposed to reach 6 RPM. but whoever set that requirement was a hopeless optimist. The size of the turret did not allow for a loading mechanism, and loading that quickly by hand was not possible. Aside from the gun, the tank had two machineguns: one coaxial and one AA machinegun on top of the turret.
The 65 ton vehicle was supposed to accelerate to 31.7 kph. In order to achieve this, the tank would have an 810 hp Meteor Mk.12 engine. As for the armour, it kept changing throughout the development process. The thickness of the upper front plate varied between 125 and 152 mm, the sides were 50 mm thick (plus spaced armour). As for the turret, the specification was only for the front, which was 254 mm (10 inches) thick.
The FV215 Heavy Anti-Tank SP No.2 was not meant to be. Morris was supposed to first build a full scale model and then two prototypes: one for mobility trials and one as a target for armour testing. In June of 1954, Vickers-Armstrong, the new owner of the contract, was given the same task. Development of the SPG continued until January of 1957. At that point, the full scale model and 80% of the blueprints were ready. But, the War Office got its own Khrushchev and the development of the FV215 Heavy Anti-Tank SP No.2 was shut down in favour of ATGMs.
Variant 4: FV4005 Stage I
As for the main subject of this article, the FV4005, work on it started a while later. Interestingly enough, the third variant was rejected outright, and designers went to the unarmoured option. This is linked to the fact that the required rate of fire of 6 RPM was unattainable without a loading mechanism. Vickers-Armstrong decided to not reinvent the wheel and use a loading system similar to the one on the 104 mm QF 127/58 SBT X1 AA gun, better known as Green Mace. The SPG with a 183 mm gun and an autoloader was known as FV4005 Stage I. An altered chassis of the Centution Mk.3 served as the base for the design. A huge trail was added to the rear, lowered during firing, and the front plate received a travel lock for the gun.
After trials that primarily tested stability of the vehicle wile firing, this design was rejected. It was decided that an SPG of this size that was completely devoid of armour was excessive, and even an automatic loader doesn't make it worth putting crewmen at such a risk. The fully rotating turret was also rather deceptive, as the powerful recoil limited the firing angle of the gun.
Variant 3: FV4005 Stage II
In July of 1955, specifications for a simpler 183 mm SPG were developed, the FV4005 Stage II. The massive automatic loader was discarded, replaced with two loader crewmen. Since even this variant couldn't carry more than 12 shells, this solution was considered acceptable. The vehicle received a massive turret. The height of the 50 ton SPG was 3.6 meters, making it the tallest vehicle built in Britain.
The turret armour was only 14 mm thick, meaning that it couldn't reliably protect the crew from even a high caliber machinegun. On the other hand, it was better than nothing. The Stage II also had a coaxial machinegun, which improved its chances against enemy infantry. A large turret was added to the rear of the turret to load ammunition. The creators of the FV4005 Stage II designed a system to rapidly supply ammunition from trucks, which somewhat compensated for the small ammunition capacity. The new turret was still installed on the Centurion Mk.3 chassis with a trail and a travel lock for the gun.
In March of 1956, the FV4005 Stage II underwent trials to determine the stability of the vehicle when shooting. 32 shots were made at various elevations in the first round. At an elevation of 0 degrees, the front of the vehicle moved up to 22 cm, and the rear up to 12 cm. The greatest oscillations were reached at an angle of 3 degrees, when the front moved up to 27 cm and the rear up to 19 cm. The trials were performed without a crew, who were replaced by mannequins. The trials showed that shooting does not injure the crew.
As a result of the trials, a list of improvements was composed, futilely. In August of 1957, the FV4005 program was closed. Various theories exist for why the super-powerful tank destroyer program was shut down. In reality, the reason was the same as with the FV215 Heavy Anti-Tank SP No.2. In 1958, the British army received Malkara ATGMs on light Humber Hornet cars. The system was much more compact and mobile, making the 183 mm SPG a relic of the past.
After completion of the trials, both FV4005 prototypes were disassembled. The Centurion Mk.3 hulls were used for other programs and the gun systems ended up in training facilities. The turret of the Stage II spent a lot of time in storage near the Bovington Tank Museum, and was only recently installed on a Centurion Mk.8 chassis. Even in this form, it is of great interest, serving as a epitaph for British tank destroyers. The FV4005 Stage II stands near the eastern entrance to the museum. Perhaps someday there will be funding to move it indoors and restore it.