The World’s Largest Caliber Tank Gun

The threat Soviet heavy tanks posed in Central Europe during the 1950s prompted the development of several measures to counter the threat. One of the most remarkable was Britain’s design of a tank with a 183mm gun, which is still the largest caliber tank gun ever made. The tank that would mount the 183mm gun was named Heavy Gun Tank No. 2 and carried the designation FV 215. It was intended to defeat any successor to the Soviet IS-3, or Stalin, heavy tank, which caused much concern at the time to western armies, although the Arab-Israeli Six Day War of 1967 subsequently showed that it was not as formidable as was earlier thought. Preliminary studies of FV 215 commenced in 1950, and in 1954, Vickers-Armstrongs, which was Britain’s longest established tank manufacturing company, was awarded a contract to build a prototype. However, FV 215 got no farther than a full-sized wooden mock-up as its development was terminated in 1957. On the other hand, the 183mm L4 gun, which was intended to arm the FV 215, was not only designed, but was actually built. Moreover, it was successfully fi red in 1955. Since the FV 215 had not been built, the 183mm gun was mounted instead on the chassis of the contemporary British medium tank, the Centurion. In one case, the installation took the form of an open mounting atop the Centurion hull and incorporated a six-round drum magazine. In another case, the gun was mounted in a tall, slab-sided turret. Both of these experimental installations were given the designation of FV 4005, as if they were part of the Centurion FV 4000 series. The choice of a rifl ed tank gun with a caliber of as much as 183mm was inspired by the high opinion held at the time in Britain of the relative effectiveness of squash head, or high-explosive squash head (HESH), which the U.S. Army subsequently called high-explosive plastic (HEP). HESH ammunition was originally developed in England during World War II by Vickers-Armstrongs for use against concrete fortifi cations. Its use was abandoned toward the end of the war and interest in it only revived some time after its abandonment. The revival came around 1950 with the development by the British army of the Heavy Gun Tank No.1, or FV 214, which preceded the design of FV 215. This tank, which was later called Conqueror, was to be capable of defeating the Soviet IS-3 and for this purpose, a gun of 120mm was considered necessary; however, the British army had not yet developed a gun of this size. In consequence, it made the decision to adopt the 120mm gun, which was being developed at the time for the U.S. T43 (later M103) heavy tank. However, the British army decided to develop its own, and what was then new, type of ammunition. The contemporary U.S. 120mm rifl ed tank guns were derived from an earlier heavy anti-aircraft gun, and like others of their generation, were still designed to fi re full-caliber armor-piercing (AP) and high-explosive (HE) ammunition. But when the British army adopted the U.S. gun, it decided to replace the AP with the armor-piercing discarding sabot (APDS) ammunition, which was already used with the 83.8mm gun of the Centurion medium tanks. The Centurion fi red APDS projectiles with a muzzle velocity of 1465 m/s (4807 ft/s), which was higher than any other tank gun projectile had fi red, making APDS the most effective type of kinetic energy AP ammunition at the time. At the same time, the British army decided to replace the HE, which the U.S. gun was designed to fi re by HESH. It considered the HESH to be relatively more effective and, in particular, more versatile as it could be effectively used against hostile tanks as well as other targets. Since then, HESH has been the standard secondary type of British tank gun ammunition and it is used to this day in preference to the shaped charge-based high-explosive antitank (HEAT) or multipurpose ammunition used in U.S. and other tanks. Once the use of HESH ammunition was satisfactorily established with the 120mm gun of the Conqueror, it was possible to consider its use as more than a complement to kinetic energy armor-piercing ammunition. In fact, in larger caliber, it could make the latter redundant, which led to the idea of developing the large caliber 183mm gun that fi red only HESH. The gun fi red massive, 160-pound projectiles, with a muzzle velocity of 716 m/s (2350 ft/s), that were heavy enough to kill any hostile tank. The choice of the somewhat odd 183mm caliber was driven by other factors. It was the outcome of a simple, metric conversion of 7.2 inches, which was the caliber of the gun/howitzers that formed the equipment of the heavy regiments of the royal artillery during World War II, and was later used for the development of large HESH projectiles. How effective the 183mm HESH would have been in combat will never be known, but the British army retained considerable faith in HESH even after it abandoned further development of the L4 gun. This was illustrated by the British army adopting the heavy Malkara anti-tank guided missile with an even larger, 8-inch (203mm) diameter HESH warhead, in contrast to all other anti-tank guided missiles, which have had shaped charge warheads. Although the development of the 183mm L4 gun was abandoned in the 1950s, at least one example of this remarkable gun has been preserved together with the experimental turret in which it was mounted. Both are now at the British National Tank Museum at Bovington in southwest England, the home of British armor. The turret, along with the gun, has been remounted on a Centurion tank chassis, and work on restoring the FV 4005 confi guration has commenced. The British National Tank Museum, which dates from the 1920s, is the oldest tank museum in the world and has 248 British, U.S., and German tanks, as well as other tanks and armored vehicles. These vehicles will be displayed in new buildings, which are part of the museum’s expansion project, made possible by a fi nancial grant from the National Heritage Fund. Richard M. Ogorkiewicz is a visiting professor at the Defence Academy of the United Kingdom, Shrivenham, England. He received a B.S. and an M.S. from the University of London. He is also a trustee of the British National Tank Museum, has authored three books on armor, and has contributed 78 articles to ARMOR. The World’s Largest Caliber Tank Gun by Professor Richard M. Ogorkiewicz July-August 2008 — 53 Photo courtesy The Tank Museum, Bovington, England