Rheinmetall 120 mm gun

The Rheinmetall 120 mm gun is a smoothbore tank gun designed and produced by the West German Rheinmetall-DeTec AG company, developed in response to Soviet advances in armor technology and development of new armored threats. Production began in 1974, with the first version of the gun, known as the L/44 as it was 44 calibers long, used on the German Leopard 2 tank and soon produced under license for the American M1A1 Abrams and other tanks. The American version, the M256, uses a coil spring recoil system instead of a hydraulic system. The gun has also been exported to South Korea and Japan for their indigenous tank designs, as well as other nations that have procured the Leopard 2 and the M1 Abrams. The 120 mm gun has a length of 5.28 m, and the gun system weighs approximately 3317 kg.

By 1990 the L/44 was not considered powerful enough to deal with the future Soviet armour, which stimulated an effort by Rheinmetall to develop a better main armament. This first revolved around a 140 mm tank gun named Neue Panzerkanone 140 ("new tank gun 140"), but later turned into a compromise which led to the development of an advanced 120 mm gun, the L/55, based on the same internal geometry as the L/44 and installed in the same breech and mount. The L/55 is 1.3 m longer, giving an increased muzzle velocity to ammunition fired through it. As the L/55 retains the same barrel geometry, it can fire the same ammunition as the L/44.

This gun was retrofitted into German and Dutch Leopard 2s, and chosen as the main gun of the Spanish Leopard 2E, the Greek Leopard 2HEL, and South Korean K2 Black Panther battle tank. It has been tested on the British Challenger 2 as a potential replacement for its current weapon, the rifled L30 120 mm cannon. This test however has been stopped due to the characteristics of the Challenger 2.

A variety of ammunition has been developed for use by tanks with guns based on Rheinmetall's original L/44 design. This includes a series of kinetic energy penetrators, such as the American M829 series, and chemical energy anti-tank warheads. Recent ammunition includes a wide range of new anti-personnel rounds and demolition munitions, giving tanks armed with the L/44 and its derivatives greater versatility on the modern battlefield. The LAHAT, developed in Israel, is a gun-launched missile which has received interest from Germany and other Leopard 2 users, and is designed to defeat both land armour and combat helicopters. The Israelis also introduced a new anti-personnel munition which limits collateral damage by controlling the fragmentation of the projectile.

Background
Worried about the inability of the 105 mm L7 tank gun then in use across NATO forces to penetrate new Soviet armor, Rheinmetall began development of a new tank gun in 1965. The first instance of a larger Soviet tank gun was witnessed on the chassis of a modified T-55 in 1961. In 1965, the Soviet Union's T-62 made its first public appearance, armed with a 115 mm smoothbore tank gun. The Soviet decision to increase the power of its tank's main armament had come when, in the early 1960s, an Iranian tank commander defected over the Soviet border in a brand-new M60 Patton tank, which was armed with the British Royal Ordnance L7. Despite the introduction of the T-62, in 1969 their T-64 tank was rearmed with a new 125 mm tank gun, while in 1972 Nizhny Tagil began production of the T-72 tank, also armed with the 125 mm gun. For example, at the fighting at Sultan Yakoub, during the 1982 Lebanon War, the Israeli government claimed to have destroyed nine Syrian T-72s with the Merkava main battle tank, armed with an Israeli production version of the American M68 105 mm tank gun (which in turn was based on the British L7). Whether or not true, the Soviets test-fired a number of Israeli M111 Hetz armor-piercing discarding sabot rounds at Kubinka, finding the 105 mm round was able to perforate the T-72's sloped front section plate but not its turret armor. In response, the Soviets developed the T-72M1. This led Israel to opt for a 120 mm tank gun during the development process of the Merkava III main battle tank. This case is similar to the American decision to replace the M68 105 mm tank gun with Rheinmetall's 120 mm gun in 1976; the introduction of the T-64A had raised the question within the armor community whether the new ammunition for the existing gun caliber could effectively deal with the new Soviet tank.

In 1963 Germany and the United States had already embarked on a joint tank program, known as the MBT-70. The new tank carried a three-man crew, with the driver in the turret, an automatic loader for the main gun, a 20 mm autocannon as secondary armament, an active hydropneumatic suspension and spaced armour on the glacis plate and the front turret. The new tank concept also had improved armament, a 152 mm missile-launching main gun, designed to fire the MGM-51 Shillelagh anti-tank missile. However, the German Army was interested in a tank gun which could fire conventional ammunition. Although there were attempts to modify the 152 mm tank gun to do so, the process proved extremely difficult, and the Germans began development of the future Rheinmetall 120 mm gun instead.



In 1967 the German Ministry of Defense decided to re-open a Leopard 1 improvement program, known as the Vergoldeter Leopard ("Gilded Leopard"), later renamed the Keiler ("Wild Boar"). Krauss-Maffei was chosen as the contractor, and two prototypes were developed in 1969 and 1970. This program grew into the Leopard 2; the first prototype of the new tank was delivered in 1972, equipped with a 105 mm smoothbore main gun. Between 1972 and 1975 a total of 17 prototypes were developed. The new 120 mm gun's ten-year development effort, which had begun in 1964, ended in 1974. Ten of the 17 turrets built were equipped with the 105 mm smoothbore gun, and the other seven were equipped with the larger 120 mm gun. Another program aimed to mount the 152 mm missile-gun was also developed in an attempt to save components from the MBT-70, but in 1971 the program was ended for economic reasons. Instead, the Germans opted for Rheinmetall's 120 mm L/44 smoothbore tank gun.

Design features
Rheinmetall's L/44 tank gun has a caliber of 120 mm, and a length of 44 calibers (5.28 m). The gun's barrel weighs 1190 kg, and on the M1 Abrams the gun mount weighs 3317 kg, while the new barrel (L/55) is 55 calibers long, 1.30 m longer. The bore evacuator and the gun's thermal sleeve, designed to regulate the temperature of the barrel, are made of glass-reinforced plastic, while the barrel has a chrome lining to increase barrel life. Originally the gun had a barrel life of between 400 and 500 rounds, but with recent advances in propellant technology the average life decreased to 260 rounds. In some cases, barrels have had to be replaced after firing only 50 projectiles. The gun's recoil mechanism is composed of two hydraulic retarders and a hydropneumatic assembly.

Rheinmetall L44 120mm
Production of the German Leopard 2 and the new 120 mm tank gun began in 1979, fulfilling an order for the German Army. Although the American M1 Abrams was originally armed with the M68A1 105 mm gun (a version of the L7), the United States Army had planned to fit the tank with a larger main gun at a later date, and the tank's turret had been designed to accommodate a larger 120 mm gun. The larger gun was integrated into the M1A1 Abrams, with the first vehicle coming off the production line in 1985 The gun, known as the M256, was based on the L/44 tank gun, although manufactured at Watervliet Arsenal and modified to increase the resistance of the barrels to fracture and fatigue. Tanks armed with versions of Rheinmetall's gun produced under licence include Japan's Type 90 and South Korea's K1A1. The gun had made a huge turn in technological history.

Rheinmetall L55 120mm


The appearance of new Soviet tanks such as the T-80B during the late 1970s and early 1980s demanded the development of new technologies and weapons to counter the threat posed to Western armor. The T-80B had increased firepower and a new composite ceramic armor. The T-72 also went through a modernization program in an attempt to bring it up to the standards of the T-80B. In 1985 the new T-72B version entered production, with a new laminate armor protection system; its turret armor,designed primarily to defeat anti-tank missiles, surpassed the T-80B's in protection.

The German government began the development of the Leopard 3, although this was canceled after the fall of the Soviet Union. On 29 October 1991, the governments of Switzerland, Netherlands and Germany agreed to cooperate in the development of a modernization program for the Leopard 2. Part of this program included the introduction of a longer 120 mm tank gun, a cheaper alternative to a brand new tank gun, increasing the maximum range of the gun by an estimated 1500 m. Although the gun is longer, allowing for a higher peak pressure from the propellant, the geometry remains the same, allowing the gun to fire the same ammunition as that fired from the shorter version. The longer barrel allows ammunition to attain higher velocities; for example, with new kinetic energy penetrators ammunition can reach velocities of around 1750 m/s. The new barrel weighs 1347 kg.

The longer tank gun has been retrofitted into the Leopard 2, creating a model known as the Leopard 2A6. Both the Spanish Leopard 2E and the Greek Leopard 2HEL, as derivatives of the Leopard 2A6, use the 55 caliber-long tank gun.

Ammunition


A variety of rounds have been developed for Rheinmetall's tank gun. For example, a long line of armor-piercing discarding sabots was developed by Rheinmetall. Originally, the Leopard 2 was outfitted with the DM23 kinetic energy penetrator, based on the Israeli M111 Hetz. The DM23 was eventually replaced by the DM33, which was also adopted by Japan, Italy, Netherlands and Switzerland. The DM33 has a three-part aluminum sabot and a two-part tungsten penetrator, and is said to be able to penetrate 560 mm of steel armor at a range of 2000 m. The DM43 is a further development of this round, co-developed between Germany and France. The introduction of the longer barrel came hand in hand with the introduction of a new kinetic energy penetrator, the DM53. Weighing in at 8.35 kilograms with a 38:1 length to diameter ratio and with a muzzle velocity of 1750 m/s, the projectile has an effective engagement range of up to 4000 m. A further development, called the DM63, improved upon the round by introducing a new temperature-independent propellant, which allows the propellant to have a constant pattern of expansion between ambient temperatures inside the gun barrel from -47 C to +71 C. The new propellant powders, known as surface-coated double-base (SCDB) propellants, allow the DM63 to be used in many climates with consistent results. The new ammunition has been accepted into service with the Dutch and Swiss, as well as German, armies.

The United States developed its own kinetic energy round using a depleted uranium penetrator known as the M829, followed by improved versions. An immediate improvement, known as the M829A1, was called the "Silver Bullet" after good combat performance during the Gulf War against Iraqi T-55s, T-62s and T-72s. The M829 series centers around the depleted uranium penetrator, designed to penetrate enemy armor through kinetic energy and to shatter inside the turret, doing much damage within the tank. In 1998 the United States military introduced the M829A2, which has an improved depleted uranium penetrator and composite sabot petals. In 2002, production of the M829A3 began, which is said to be able to defeat the latest versions of Russian explosive reactive armor.

Both Germany and the United States have developed several other rounds. These include the German DM12 multi-purpose anti-tank projectile (MPAT), based on the technology in a high explosive anti-tank (HEAT) warhead. However, it has been found that the DM12's armor-killing abilities are limited by the lack of blast and fragmentation effects, and that the round is less valuable against lightly armored targets. The United States also has a MPAT type projectile, known as the M830. This was later developed into the M830A1, which allows the M1 Abrams to use the round against helicopters. The M1 Abrams can use the M1028 canister round, which is an antipersonnel munition, packed with over 1,000 tungsten balls. The United States Armed Forces accepted a new demolition round, called the M908 Obstacle Defeating Round, based on the M830A1 MPAT, but with the proximity fuse replaced by a hardened nose cap. The cap allows the round to impact and embed itself in concrete, then exploding inside the target and causing more damage.

The Israeli Army introduced a new round known as the Laser Homing Anti-Tank (LAHAT) projectile. Using a semi-active laser homing guidance method, the LAHAT can be guided by the tank's crew or by teams on the ground, while the missile's trajectory can be selected to either attack from the top (to defeat enemy armor) or direct attack (to engage enemy helicopters). Furthermore, the missile can be fired by both 105 mm and 120 mm tank guns. The LAHAT has been offered as an option for the Leopard 2, and has been marketed by both Israel Military Industries and Rheinmetall to Leopard 2 users. Israeli Merkavas make use of a round known as the APAM, which is an anti-personnel munition designed to release fragmentation at controlled intervals to limit the extent of damage. Fragments are shaped to have enough kinetic energy to penetrate body armor.

Poland has introduced a series of projectiles for Rheinmetall's tank gun, including an armor-piercing penetrator target practice round (APFSDS-T-TP), a high-explosive round, and a high-explosive target practice (HE-TP) projectile. The ammunition is manufactured by Zakłady Produkcji Specjalnej Sp.

Operators
Due to tank sales, Rheinmetall's L/44 tank gun has been manufactured for other nations. For example, the Leopard 2 armed with the 44 caliber long gun, has been sold to the Netherlands, Switzerland, Sweden, Spain, Austria, Denmark, and other countries. Egypt had manufactured 700–800 M1A1 Abrams by 2005, and in 2008 requested permission to build another 125 tanks; their M256 main guns (the US version of the L/44) were manufactured by Watervliet Arsenal. The M1A1 has also been exported to Australia, while the M1A2 Abrams has been exported to Saudi Arabia and Kuwait.

The Leopard 2A6 and its longer L/55 main gun have been exported for use by the Canadian Army, and the Netherlands upgraded part of its original fleet of Leopard 2s with the more powerful armament. The British Army has tested Rheinmetall's longer gun, possibly looking to replace the current L30A1 120 mm L/55 rifled main gun on the Challenger 2. Two Challenger 2s were modified to undergo firing trials. World Industries Ace Corporation is also producing the L/55 under license for the K2 Black Panther.