The 140mm smoothbore Advanced Tank Cannon (ATAC) System consists of the XM291 gun, the XM91 autoloading system and a family of 140mm ammunition.
The ATAC System was expected to be the main armament of the US Army's future Block III MBT, a key part of the projected Armored Systems Modernisation.
The ATACS is being installed in the Component Advanced Technology Test-Bed (CATT-B). This is based on an M1A1 Abrams chassis and, in addition to the ATAC System, has Advanced Integrated Propulsion System (AIPS), hydropneumatic suspension, Standard Army Vetronics Architecture, Rockwell Multi-sensor Target Acquisition Sensor, CDC ADA based fire control system, lightweight track, modular armour, advanced chemical agent alarm, NBC collective protection system and a Vehicle Integrated Defense System with countermeasures, threat sensors and smoke.
Prior to being installed in the CATT-B, the ATAC System has been installed in a modified M1 turret on a standard M1 chassis. This also features the Benet Laboratory designed automatic loader, modified M1A1 fire control electronics, Rockwell Multi-sensor Target Acquisition Sensor (qv), standard M1 gunner's primary sight and a new fire control computer. In this vehicle the gunner is on the right, as in the M1, while the tank commander is on the left in the space normally occupied by the loader.
The XM291 gun is a solid propellant tank gun with an integral mount and recoil mechanism that fires two-piece (projectile and charge) ammunition with twice the muzzle energy of the standard 120mm M256 gun installed in the current M1A1 and M1A2 Abrams MBTs. The ordnance is fitted with a thermal sleeve, fume extractor and is 91 kg lighter than the standard 120 mm M256 ordnance.
By means of a simple tube change, which takes one hour to accomplish, the system can also fire 120 mm one-piece conventional and advanced ammunition.
During operation of the XM91 autoloading system, developed by the US Army's Benet Laboratory, the selected ammunition type is identified, the telescoped cell containing that cartridge is moved to the loading port and the loading door is opened. The rammer mechanism then moves forward and grasps the rim of the stub base, the round gripper mechanism which holds the cartridge in place is released and the inner cell moves forward.
Docking of the inner cell with the breech occurs on full extension and the round is seated in the gun. The ram head and the inner cell then retract to their original position and the loading door is closed. The downloading sequence is similar and an ammunition re-arm port is provided at the rear of the autoloader for that procedure.
The ammunition transfer mechanism has been developed by Martin Marietta with the ready use bustle-mounted magazine holding 17 120mm or 140mm rounds, with the hull magazine holding 22 140 mm two-piece rounds as components or 33 single-piece 120 mm rounds.
Automatic loading takes place at the rate of 8 to 12 rds/min, with the rammer being provided by Brunswick Defense (qv).
The ATAC System family of ammunition consists of three cartridges: the XM964 kinetic energy (KE) cartridge; the XM965 chemical energy (CE) cartridge; and the XM966 training cartridge for both rounds.
Each cartridge consists of a forward and rear component. The rear component, which is identical to all three cartridges, consists of a stub base and primer assembly (similar to that of a standard 120mm cartridge), a combustible side wall, an ignition system and propellant.
The forward component houses the appropriate projectile, partially telescoped within the primary propelling charge, and propellant in a combustible cartridge case which also contains a relay charge at its base for the transfer of ignition from the rear component. A snap joint joins the two components allowing cartridge removal from the breech. The cartridges offer a muzzle energy that is double that of the standard 120mm system.
Switzerland has successfully carried out firing trials of a new Swiss designed and built 140mm smoothbore tank gun installed in a Leopard 2 MBT of the Swiss Army.
Switzerland has a total of 380 Leopard 2 MBTs designated the Panzer 87 (Pz 87 Leo), of these 380, 35 came direct from Krauss-Maffei of Munich and the remainder were manufactured under licence by Swiss industry with final deliveries being made in 1993.
The Leopard 2 is armed with a German Rheinmetall 120mm smoothbore gun which fires two types of ammunition, Kinetic Energy (KE) Armour-Piercing Fin-Stabilised Discarding Sabot - Tracer (APFSDS-T) and Chemical Energy (CE) High Explosive Anti-Tank Multipurpose Tracer (HEAT-MP-T). Both of these ammunition types have a semi-combustible cartridge case and all that remains after firing is the short case stub.
In the late 1980s, k + w Thun (Swiss Federal Armament Works Thun) started a development programme to demonstrate the feasibility of a more powerful gun, not only to upgrade the Leopard 2 but also to be used as a fortress weapon.
At the same time, the weapon was to be used to prove the anticipated performance of the ammunition and to integrate the gun and its associated ammunition into existing MBTs with minimal costs being involved.
The experimental ammunition for the 140mm smoothbore tank gun was developed by the Swiss federal ammunition factories in co-operation with partners of other nations.
First ballistic verification of the Swiss 140mm smoothbore gun under live conditions took place in the Summer of 1988 with the first projectiles being fired from the weapon installed in a Leopard 2 MBT taking place in the Autumn of 1989.
To ease handling, the ammunition is in two parts. The main propellant charge has a steel bottom and a combustible container with about 10 kg of propellant, and one part with either a KE projectile plus an additional 5 kg of propellant or a Multipurpose (MP) round which would probably not require the additional charge. The propellant will be optimised for the KE projectiles.
The KE projectile has a long rod penetrator of conventional material, not depleted uranium as used in US projectiles of this type, and a sabot with a plastic driving band. The first experimental MP round is a shaped charge with an additional strong fragmentation effect.
The chamber of the Swiss 140 mm smoothbore gun is somewhat shorter than the NATO layout but in order to keep the volume within the present international trend it has a larger diameter.
According to k + w Thun, its 140 mm smoothbore gun and projectiles can be adapted within a short space of time, if required to do so by international standardisation of the chamber.
Development efforts on the ammunition side have been concentrated on analysis of the terminal ballistics of KE projectiles with various designs (length, diameter, weight and velocity) against several types of test target. At the same time, the effect of the MP rounds was also investigated in static tests.
Trials so far have shown that both types of ammunition will penetrate around 1,000 mm of steel armour, which is a significant increase in penetration over current in-service 120 mm projectiles.
It is stressed that the Swiss 140 mm smoothbore gun is at present a research gun and has not yet been fully developed, and given the reduced threat since the weapon was conceived, it is not likely to be deployed in the near future.
Under contract to the BWB, Rheinmetall has built six prototypes of a 140mm smoothbore gun and its associated APFSDS-T ammunition for trials purposes.
This development contributes to the international Future Tank Main Armament (FTMA) programme, as defined in the quadrilateral MoU between France, Germany, UK and the USA.
The new 140mm smoothbore gun is called the NPzK-140 and is fitted with a vertical sliding breech mechanism, thermal sleeve and a fume extractor.
If the threat changed in the future, the German Army would have the option for a firepower improvement programme for the Leopard 2. The installation of a 140 mm gun would probably require the installation of a new turret fitted with an automatic loader to handle the separate loading 140 mm ammunition.
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