By 1990, the L/44 was not considered powerful enough to defeat future Soviet armour, which stimulated an effort by Rheinmetall to develop a better main armament.

The LAHAT, developed in Israel, is a gun-launched anti-tank guided missile which has received interest from Germany and other Leopard 2 users.

The Israelis also introduced a new anti-personnel munition which limits collateral damage by controlling the fragmentation of the projectile.

[14] The new tank concept also had improved armament, a 152-millimetre (6.0 in) missile-launching main gun, designed to fire the MGM-51 Shillelagh anti-tank missile.

[17] This program grew into the Leopard 2; the first prototype of the new tank was delivered in 1972, equipped with a 105-millimetre (4.1 in) smoothbore main gun.

Tanks armed with versions of Rheinmetall's gun produced under licence include Japan's Type 90[33] and South Korea's K1A1.

[35] The appearance of new Soviet tanks such as the T-80B during the late 1970s and early 1980s led to the development of new technologies and weapons to counter the threat posed to Western armour.

[40] On 29 October 1991, the governments of Switzerland, the Netherlands and Germany agreed to cooperate in the development of a modernization program for the Leopard 2.

In response, Rheinmetall started the development of a larger 130 mm tank gun, financed entirely using internal funding.

[46] The Rh-130 Future Gun System has a chrome-lined smoothbore barrel (initially L/51,[47] revised to L/52[48]) with a vertical sliding breech mechanism, increased chamber volume, no muzzle brake, a thermal sleeve, and a muzzle reference system (MRS) enabling it to be boresighted on a more regular basis without the crew needing to leave the platform.

The 130 mm is designed to equip the Main Ground Combat System (MGCS), a joint effort between Germany and France to produce a successor to the Leopard 2 and Leclerc, possibly to be launched between 2025 and 2030.

[50][51][52] In July 2020, Rheinmetall unveiled a testbed tank for the gun in a new turret, mounted on a Challenger 2 hull.

[53][54] In June 2022, Rheinmetall unveiled the Panther KF51 concept tank based on a Leopard 2 chassis and a redesigned turret hosting the new gun.

[48] The M256 is an American variant that uses a Rh-120 L44 gun tube and combustible cartridges with an American-designed mount, cradle and recoil mechanism.

Originally, the Leopard 2 was outfitted with the DM23 kinetic energy penetrator,[56] based on the Israeli 105 mm M111 Hetz which itself was a licensed copy of the American M735 round.

[64][65] The public appearance of the K276 armour-piercing fin-stabilized discarding sabot (APFSDS), the first 120 mm ammunition with self-sharpening penetrator, was during the release ceremony of K1A1 prototype in 1996.

An immediate improvement, known as the M829A1, was called the "Silver Bullet" after its good combat performance during the Gulf War against Iraqi T-55, T-62 and T-72 tanks.

[69] In 1998, the United States military introduced the M829A2, which has an improved depleted uranium penetrator and composite sabot petals.

[70] In 2002, production began of the ($10,000 per round) M829A3, using a more efficient propellant (RPD-380 stick),[71] a lighter injection-molded sabot, and a longer (800 mm) and heavier (10 kg / 22 lb) DU penetrator, which is said to be able to defeat the latest versions of Russian Kontakt-5 explosive reactive armour (ERA).

A further improved M829A4 round with a segmented penetrator to defeat Relikt has entered a full-rate production in December 2015.

[56] However, it has been found that the DM12's armour-killing abilities are limited by the lack of blast and fragmentation effects, and that the round is less valuable against lightly armoured targets.

The cap allows the round to impact and embed itself in concrete, exploding inside the target and causing more damage.

[2] 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 armour) or direct attack (to engage enemy helicopters).

[81] 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.

[84] In April 2024, the British Ministry of Defence announced that a statement of intent had been signed with Germany for the development of an Enhanced Kinetic Energy (EKE) armour-piercing round for both Challenger 3 and Leopard 2 tanks, as a joint venture between Rheinmetall and BAE Systems.

For example, the Leopard 2 armed with the 44 calibre long gun, has been sold to the Netherlands, Switzerland, Sweden, Spain, Austria, Denmark, Finland, and other countries.

[95] Although the South Korean K2 Black Panther is equipped with a CN08 120 mm L/55 main gun and is often misunderstood as a licensed product of the German counterpart due to its similar appearance of the gun barrel, it is indigenously developed by Agency for Defense Development (ADD) and WIA (Now Hyundai WIA), a Korea-based powertrain company affiliated with Hyundai Kia Motors Group.