Tank guns: The path beyond 120 mm

It is generally accepted that there are three key criteria in tank design, the so-called ‘iron triangle’ of firepower, protection and mobility. In this article our interest is firepower, the current state of tank armament and its potential future evolutionary path. Central to this purpose is understanding how we got to the current state of play as regards tank armament.

Western Cold War efforts

Both the US and the British would introduce heavy tanks with large guns in response to the threat of the IS-3 (ИC-3; ENG: Iosif Stalin 3), a late–Second World War Soviet heavy tank and its successors in the 1950s. The US commenced work on the M103 heavy tank project at the end of 1950s, with the vehicle entering service in 1957 and its most significant feature was the 120 mm M58 L/60 gun. Only 300 of these tanks were ever built, with the vast majority going to the US Marine Corps (USMC); the tank was withdrawn by 1974.

Britain decided to use the US 120 mm gun for its own heavy tank programme, producing it as the 120 mm L1 tank gun. This would become the main armament of the FV214 Conqueror tank, which entered service in 1955 with only 185 built, before the vehicle was retired in 1966. Britain also had another heavy tank programme in the works, one which was predicated on the use of an absolutely extraordinary gun system, the 183 mm L4 gun. The only ammunition nature developed was high explosive squash head (HESH), a two-piece round, with its performance objective being penetration of 152 mm of armour with a 60° slope at 1,829 m. No other gun was capable of this performance at this time and it was believed that any hit on a target tank would lead to destruction or total disablement.

The L4 gun was initially to be mounted on the FV4005 vehicle, described as a heavy self-propelled anti-tank Gun, with a limited traverse. The eventual aim was to have the gun mounted on the FV215 heavy tank though in the end it was decided to end the programme and opt for anti-tank missiles as the most effective solution for long-range target engagement.

Arguably the most significant Western tank armament development of this period was based on the British 20-pounder gun used in the Centurion Mk 3. This was the 105 mm L7 rifled gun, which would become the dominant Western tank gun of its era. The US would adopt the L7 and modify it to become the M68, further increasing its market dominance. The L7/M68 105 mm guns were effective systems, but as the Cold War drew on, it was clear that threat armour was advancing in terms of protection and firepower, and so a response was necessary.

An unconventional solution adopted by the US was the M81 152 mm rifled gun and the MGM-51 Shillelagh gun-launched anti-tank guided missile (GLATGM) installed on the M60A2 tank and also on the M551 Sheridan light tank, however results were less than satisfactory. Less adventurous solutions were being considered, including in Britain where the search for a follow-on to the L7 led to the development of the EXP-14 110 mm gun; this would have employed a semi-combustible cartridge case with a metallic stub, with an autoloader being considered as a part of the armament package. In the end, Britain decided on the 120 mm L11 rifled gun, using two-piece ammunition for its Chieftain tank. Britain would remain wedded to the 120 mm rifled gun and two-piece ammunition for decades, with the L11 of the Chieftain superseded by the 120 mm L11A5 on Challenger 1, and then later the L30A1 120 mm L55 on Challenger 2.

The 1960s and 1970s saw numerous efforts at collaborative tank programmes amongst NATO nations, though the end results were never encouraging. That being said, one thing to emerge from these collaborative efforts was a weapon that became the de facto NATO tank armament solution, which then spread globally. This was the Rheinmetall 120 mm smoothbore gun with the original L44 variant of the gun entering service with the Leopard 2 in 1979. It was then selected as the M256 by the US for the M1A1 variant of the Abrams that was produced from 1986, with the original M1 produced from 1978 to 1985 equipped

with the M68 105 mm gun. The indigenous French 120 mm CN-120-26/52 gun designed for the Leclerc main battle tank (MBT) was built around 120 × 570 mm rounds to have commonality with the German gun. The Korean K2 Black Panther tank, as used by the Republic of Korea (ROK) and Poland, mounts a CN-08 120 mm; this Korean-designed weapon was built around the standard NATO 120 × 570 mm round.

Beyond the standard 120 mm L/44 gun, Rheinmetall would go on to develop the longer L55 variant initially for the Leopard 2A6, with the latest variant being the L55A1 as used on the current Leopard 2A8 and Challenger 3.

Soviet and Russian developments

Soviet tank armament developments explored both conventional and unconventional solutions. A proposed heavy tank design that featured a 130 mm gun and an autoloader was halted, although the latter option would become a feature of next-generation Soviet tanks. Instead, in the early 1960s, the T-62 was introduced, which represented a change in tank armament direction since the vehicle featured the smoothbore 115 mm U-5TD (2A20) gun. Then came the T-64A with a 125 mm 2A26 (D-81T) smoothbore gun with a carousel autoloader. Various improvements were made to the 2A26, resulting in the 2A46 family, with the 2A46-1 introduced on the T-64B.

Among the improvements introduced by the new 2A46 series was the ability to launch the 9K112 Kobra gun-launched anti-tank guided missile (GLATGM) developed by KBP to allow accurate engagements at extended ranges. Soviet GLATGM developments would provide capability for

, as well as for earlier models such as the T-55 and the T-62 with the 9K116-2 Sheksna system. In parallel, improvements were made to the 2A46 gun to extract increased performance. It should be noted that Soviet technology provided the basis for current Russian and Ukrainian GLATGM systems, as well as Chinese weapons in this category.

 

At the end of the Soviet period, a number of future tank programmes featured a significant increase in firepower. The first of these was Obiekt 292 undertaken by the Kirov Plant in what was then Leningrad, and which was based on the T-80 platform. The hull was a T-80U, with the turret being a T-80BV. The vehicle was equipped with an LP-83 152 mm smoothbore gun and autoloader. Allegedly the intention had been to develop a rifled 152 mm gun, but resources were not available to pursue this approach. A single Obiekt 292 vehicle was completed in September 1990 and tested in 1991, with the LP-83 said to have delivered 50% more muzzle energy than the standard 2A46 125 mm tank gun of the era. With the collapse of the Soviet Union, the Obiekt 292 programme made no further progress.

The Nizhny Tagil tank plant, later Uralvagonzavod (UVZ), was commissioned to design a new tank for the Soviet Army at the end of the 1980s as Obiekt 195, often referred to as the T-95. It was significantly heavier than Soviet tanks of the time and was equipped with a 2A83 152 mm L55 smoothbore gun and autoloader – a different design to the Obiekt 292 gun. The collapse of the Soviet Union saw all work halted on the programme in the early 1990s, but in the early 2000s, UVZ began working on the programme once more, but official support for the project ended by the late 2000s, although UVZ did try to continue the programme as a private venture for a little while.

Another Nizhny Tagil programme was Obiekt 187, which featured improved protection and mobility compared to other Soviet tanks of the 1980s. It also featured a new gun, the 2A66 125 mm L48 smoothbore, which had more impressive performance than the standard 2A46 tank gun. In parallel with Obiekt 187, Nizhny Tagil also worked on a lower-risk tank design in the form of Obiekt 188, which would eventually go into production as the T-90. The T-90 in turn would also see the arrival of more capable GLATGMs in the form of the 9M119M Invar and 9M119M1 Invar-M.

There were a number of other Soviet-era large tank gun programmes that entered the testing phase, including the 130 mm M-65 L60 rifled gun that emerged in the 1950s. This gun system would emerge once more at the end of the 1970s in an improved version becoming part of the Obiekt 795 testing programme. This programme would also see the arrival of an early version of the 2A82 125 mm smoothbore gun.

However, it was the arrival of the UVZ T-14 Armata tank prototype in 2015, previously known as Obiekt 148, which can be said to have acted as a catalyst to recent Western tank developments. Advanced in conception and equipped with a 2A82-1M 125 mm gun offering higher performance than the 2A46 family, and capable of handling longer ammunition, the Armata represented a major advance in Russian tank capability. However, actually fielding significant numbers of these tanks appears to be beyond Russian industrial capabilities at this time.

MGCS: The way ahead?

The Franco-German Main Ground Combat System (MGCS) is a collaborative defence programme intended to meet future armour needs. Inevitably, multinational collaborative programmes are complicated, highly politicised and industrially complex. This complexity is demonstrated by the fact that there are two choices for the main gun of the MGCS tank variant, one of French origin and one of German origin; both would appear to be viable options, but there can only be one winner!

The irony is that one might suggest that both of these options can trace their lineage back to a NATO programme that got underway in the Future Tank Main Armament (FTMA) programme in the late 1980s that involved France, Britain and Germany with the objective of developing a 140 mm NATO standard smoothbore tank gun. The US would later join this NATO effort, although major British involvement would cease at a later date.

This was the era of programmes such as the US Advanced Tank Cannon (ATAC) that developed the XM291 gun designed in both 140 mm and 120 mm calibres. Elsewhere, Germany had worked on a Leopard 2 upgrade, which was the multi-stage Kampfwertsteigerung (KWS) programme. Under KWS 1 the Rheinmetall 120 mm L44 smoothbore gun was replaced by the new Rheinmetall 120 mm L55, operating at higher pressures, providing increased performance. The KWS 2 programme integrated enhanced protection features (which would be used on the Leopard 2A5). While the far more ambitious KWS 3 would see a new turret fitted with the 140 mm NPzK smoothbore gun, an autoloader and a reduced crew of three, in the mid-1990s, the KWS 3 upgrade was cancelled. On the other hand, as we shall see, France continued with serious 140 mm tank gun work through the 1990s and beyond.

Meanwhile in Germany, Rheinmetall adopted a two-track approach to tank gun development. Following the development of the Rheinmetall 120 mm L55 gun, the next step was to design improved ammunition to take advantage of the increased performance, and this saw the development of the DM73 armour-piercing fin-stabilised discarding sabot (APFSDS) round that was said to offer an 8% performance boost over the previous generation DM53 and DM63 APFSDS rounds. Even more performance could be extracted from the L55 gun and this would be achieved by a new APFSDS round, the KE2020Neo, designed to offer a 20% performance improvement over current standard APFSDS 120 mm rounds.

Rheinmetall then decided to look at possible solutions for a next-generation tank gun that would significantly surpass 120 mm L55 performance. The first evidence of their efforts in this direction was the display of a new 130 mm gun system at the 2016 Eurosatory exhibition. This particular system had been used as a firing demonstrator to explore the performance parameters of the new gun. The key objective was to have a gun system that delivered a round on to the target that had over 50% more energy than the equivalent 120 mm round. Other factors that influenced weapon design were finding the most effective combination of system weight, recoil force and barrel length. The gun system is also integrated with an autoloader, while new ammunition types are being developed such as a next-generation kinetic energy (KE) munition and a programmable multi-purpose high-explosive (HE) munition.

Rheinmetall has developed the KF51 Panther tank as an upgrade for the Leopard 2 family; Hungary is the first customer and will use the 120 mm L55A1 gun along with an autoloader system. The turret will also be able to support the integration of the 130 mm L51 gun as part of an upgrade programme at a later date. Meanwhile in Italy, a new joint-venture, Leonardo Rheinmetall Military Vehicles (LRMV), has been formed, which will use the KF51 as the basis for developing a new tank for the Italian Army, with the 130 mm gun part of the programme.

 

The other solution for the MGCS is from KNDS, based on French work on future tank armaments both nationally and in connection with FTMA. By the mid-1990s, a 140 mm smoothbore gun system had been integrated with a specially modified Leclerc turret with autoloader, which potentially could have paved the way for a future Leclerc modernisation programme. However, the size of the ammunition, being more than 50% longer, as well as heavier than a standard 120 mm APFSDS round, would make it complex to offer as a simple upgrade. This would eventually lead to work on developing a more dimensionally efficient ammunition solution and towards maximising gun performance.

By Eurosatory 2022, KNDS was showcasing the 140 mm ASCALON gun for the first time, a system previously rooted in FTMA development. However, at that point it was clear that the 140 mm gun was a work in progress, as KNDS looked at evolving MGCS requirements and both current and future threat assessments. One important element was the evolutionary capabilities of the gun, as the gun shown in 2022 had the capability to accommodate a significant increase in chamber pressure to provide higher projectile velocity and extended engagement range. To take full advantage of this would require ammunition enhancements, something that KNDS was working on in parallel.

By Eurosatory 2024, the ASCALON gun had undergone two years of development work and the 140 mm version was joined by a 120 mm version. Though the ASCALON 120 mm L58 gun can use all existing 120 × 570 mm NATO ammunition, KNDS have a new SHARD APFSDS round which offers a considerable performance increase over current rounds of this type. The 120 mm ASCALON variant can be easily and rapidly upgraded to the 140 mm version. According to media reports, KNDS suggested that the 140 mm gun could, because of its higher muzzle energy, deliver a round with as much as 70% more energy on to the target than a standard 120 mm round. The rounds displayed in 2024 also appeared slightly shorter than those shown in the mid-1990s.

Complicated international programmes like the MGCS future tank programme and the SCAF combat air system are inevitably highly political. MGCS programme timings have already slipped and that inevitably adds uncertainty into the long-term health of the programme. Despite this, both KNDS and Rheinmetall appear capable of providing viable gun solutions for MGCS. In the meantime, upgrading existing tanks by replacing current generation 120 mm gun systems offers a potential market while an MGCS decision remains pending.

 

Both of the guns being suggested for MGCS will have the capability to engage targets at extended ranges, with beyond line-of-sight capabilities mentioned. This opens the way for the adoption of new GLATGMs, presumably one of the reasons why MBDA unveiled the Akeron MBT 120 system at the DSEI exhibition in September 2025. This is a non-line-of-sight missile for smoothbore 120 mm guns, featuring a low-smoke motor and a passive infrared (IR) seeker. The system is ITAR-free (allowing it to be exported without approval by Washington DC) and uses commercial-off-the-shelf components, meaning that an in-service variant of the missile could be rapidly developed to meet customer demand. Other GLATGM solutions are available from or being developed by India, Israel, Türkiye and the Republic of Korea, amongst others.

David Saw