XM291 Advanced Tank Cannon

The XM291 Advanced Tank Cannon (ATAC) is an American smoothbore cannon that has been in development since 1985. It is intended as the future main armament for main battle tanks. The weapon can fire both 120 mm and 140 mm ammunition by simply changing the barrel. A 120 mm variant with electrothermal-chemical drive technology (ETC) is also in development. To save weight and to enable a better balance, the weapon barrel is made of a composite material.

Development history

U.S. Army Concepts for the ASM Program Heavy Platform (1991)

When NATO found out about the introduction of the T-80 for the Warsaw Pact armed forces and its design in 1983 , they were surprised because they expected a revolutionary design like the one at the introduction of the T-64 , but were disappointed by an evolutionarily advanced vehicle. In order to be able to better assess the threat situation, Soviet main battle tanks were postulated to follow the T-80. These were referred to as the Future Soviet Tank , or FST for short:

FST-1: Designates the T-80U and the T-72B , as a combat value enhancement of established models.
FST-2: Main battle tank with an unmanned turret and a crew of 2–3 men in the hull, blinding laser and immune to anti-tank ammunition from NATO (existing at the time). The potential threat led to the introduction of the M1A1HA with uranium armor.
FST-3: The vehicle was intended to outclass existing main battle tanks such as the M1 Abrams. A cannon with a muzzle energy of 18 MJ was considered necessary to destroy the FST-3.

With the aim of reducing operating costs, the US Army planned in the mid-1980s to develop and build 24 combat vehicles at the same time. The standardization of the components promised cost advantages from this Armored Family of Vehicles Program . However, it quickly became clear that this measure would go beyond budget, so in March 1985 an agreement was reached on a heavy platform (four vehicles) and a medium platform (two vehicles). In February 1990, a light armored gun system was advertised, with the M8 armored gun system winning the competition. The central element of the development program known as the ASM program was the Block III tank, which the FST-3 was to counter. Since the Future Infantry Fighting Vehicle (FIFV) armored personnel carrier version was also to be developed on the basis of the heavy chassis, a division of the heavy chassis into a front- and rear-wheel drive variant was also considered. Ultimately, however, an agreement was reached on a heavy unit tank with a front engine.

In 1985 the development of the XM291 began in order to achieve the required destruction performance compared to the FST-3. At the same time, the US Army started development programs for the battle tank weapon system, which led to the TTB (Tank Test Bed) and CATTB (Component Advanced Technology Test Bed) prototypes. The CATTB was tested from 1987 to 1988 and was able to demonstrate the successful use of the 140 mm XM291 cannon and the XM91 autoloader. One vehicle is still parked at the Aberdeen Proving Ground for testing. The further development of the 140 mm variant was discontinued in 1992 after the collapse of the Eastern Bloc, only the 120 mm version with powder and ETC technology is further improved. In January 2000, a 120 mm L / 55 ETC cannon XM291 achieved a muzzle energy of 17 MJ and thus an important milestone. Further tests were carried out in August 2004 when an M8 AGS equipped with a serial hybrid drive called "Lightning Bolt" fired seven modified M829A2 APFSDS rounds from the ETC cannon. The M129 propellant charge lighter was replaced by a coaxial plasma injector.

technology

Weapon system

The XM291 ATAC was developed by Benet Laboratories and Watervliet Arsenal (WVA), drawing on experience with the 105mm XM35 drawn barrel cannon. Above all, the design of the lock, recoil absorber and smoke evacuator was adopted. In order to allow the M1 Abrams an uncomplicated increase in firepower, the dimensions are comparable to the M256. The lock with tube holder, trunnion and recoil dampers is the same for all versions. The tube retainer and lock can move on 40 in. (1016 mm) long tube return rails to accommodate the recoil forces . A maximum braking force of up to 1,200 kN is achieved. The shutter alone weighs 1,300 pounds (590 kg). The design of the lock was adopted from the XM35 and is called the EX35 there. In contrast to the M256, which uses a simple drop wedge lock, the XM291 uses a screw lock with an interrupted thread, which opens vertically. As a result, the material at the point of contact between the closure and the pipe holder is less stressed than if a conventional drop wedge closure were used, which extends the service life.

The barrel, which contains the barrel and cartridge chamber, can be designed for either 140 mm or 120 mm ammunition, with a barrel change taking an hour. The 120 mm, 55 caliber tube weighs 3,200 pounds (1452 kg) and has a 30 pound (13.6 kg) smoke evacuator between 125 and 160 inches (3175 to 4064 mm) measured from the rear of the pipe . Located 259 inches (6579 mm) from the rear of the tube is the 12.4 pound (5.6 kg) collimator of the field aligner. Despite the larger caliber length, the weapon system is 91 kg lighter than the M256 cannon and thus weighs 3689 kg. Compared to the 120 mm L / 55 from Rheinmetall (M256E1), which weighs 4160 kg, the weight saving is significant. The mass of the 140 mm tube with 47 caliber lengths has not been published, but is likely to be around 40% higher.

The tube is made of a composite material to save weight and allow a better balance of the weapon system. In 1987 and 1988, steel pipes with a shell made of carbon fiber-reinforced plastic , which used bismaleimide as a matrix material, were examined at the Benet Laboratories and in the Watervliet Arsenal . In later years, a steel tube with an MMC jacket was used. Here, 0.14 mm thick silicon carbide fibers are wrapped around the forged tube, and during the process these are coated with aluminum 6061 in a plasma spray process . The volume fraction of SiC is around 47% at the end. The end product is then gradually printed and finally subjected to an autofrettage . To the residual stress to reduce the tube is then heated. For reasons of corrosion protection and to ensure better adhesion, the intermediate layer - i.e. the outside of the steel pipe - is coated beforehand with a 0.25 to 0.5 µm thick layer of nickel, silver and an aluminum-silver alloy with 10% silver .

The tube is then provided with a heat protection sleeve to reduce the influence of wind and weather on the weapon system. As a special feature, the “Dynamically Tuned Shroud (DTS)” concept was tested to reduce the natural vibrations of the weapon. The front part of the heat protection sleeve, which according to the patent is made of thin aluminum, is attached to the smoke evacuator using a clamping ring. The front end is connected to the tube via radial spiral springs. These are attached to the heat protection sleeve with screws, which can be used to set the spring stiffness and thus the vibration behavior. A thin layer of rubber is installed at the transition point between the springs and the ring of the thermal insulation for damping. In 2001 driving tests with the M1A1 were carried out at the Aberdeen Proving Ground. However, no test shots were fired because the system was not robust enough. In later tests with the M256E1, the coil springs were replaced by leaf springs, also in order not to affect the line of sight of the field adjustment system. After test shots, a further improved version without adjusting screws was developed.

In order to examine the precision and vibration behavior of the XM291, shooting tests were carried out before 1990 with the newly developed KE ammunition XM866 and HEAT ammunition XM831. The requirement was that the curvature of the entire barrel should not exceed 0.05 inches (1.27 mm), or 0.01 inches (0.25 mm) on a 25 inch (635 mm) tube length. The deflection due to its own weight is not taken into account. These precision figures are significantly above the usual, previously valid values for tank cannons. During the test shots, the muzzle swung 0.005 inches (0.127 mm) when firing the XM321 HEAT and 0.0015 inches (0.038 mm) in the XM866 KE. This corresponds to a deviation of 0.05 milliradians (0.0028 °) and is negligible compared to the accepted value of 0.25 mil (0.014 °) for tank cannons. However, this is only about the inaccuracy of the pipe, other factors such as the stabilization system and dynamic loads caused by the journey are not included.

Loading machines

Since the two-part 140 mm ammunition can only be transported with difficulty by a loader into the cartridge chamber and the work of a human loader is very difficult when driving quickly off-road, the use of the XM291 ATAC was always planned together with a loading machine. The 120 mm version, which came into focus later, can theoretically also be loaded by hand, as is already common today. The autoloaders designed for the CATTB and the Block III battle tank are briefly described here:

CATTB: The Component Advanced Technology Test Bed was intended to test part of the technology that was to be installed in the Block III main battle tank. At the same time, an increase in combat value for the M1 Abrams should be shown. For this purpose, the Advanced Integrated Propulsion System (AIPS) was integrated into the tub and additional dust aprons were attached to the side aprons. The turret front, sides and roof armor were massively reinforced and the 140 mm XM291 powder cannon with the XM91 automatic loader installed. A better fire control system was considered, but could not be realized within the budget.

The XM91 autoloader works as follows: In the rear of the tower, which had to be extended to the rear because of the longer 140 mm projectiles and which includes the space of the storage basket, there are two drums of the FASTDRAW magazine on the left and right. The drums are separated by an armored wall so that the ammunition bunker in the rear of the tower is divided into two parts. Two blow-out panels are attached to the tower roof for each drum. Due to the honeycomb construction of the drums, they have a high packing density and a low weight. Each drum can hold 17 or 18 cartridges (depending on the source), so there are 34–36 rounds ready. The loader’s space is taken up by a kind of industrial robot . This places the loading cradle on one of the two output windows, moves a gripper into the ammunition container and pulls the ammunition from the magazine into the loading cradle. The loading robot then moves behind the cartridge chamber of the XM291 through lateral movements. The chain fitter now rams the ammunition into the cartridge chamber and the weapon locks. The loading robot moves away to the side, after the shot the cycle starts all over again. The system can achieve a rate of eight to twelve rounds per minute.

Block III tanks: A consortium led by General Dynamics Land Systems (GDLS) received an order from the US Army in December 1990 to develop a next-generation main battle tank. In contrast to the Panzerkampfwagen 2000 , the vehicle was designed as a front-wheel drive with an LV100 gas turbine, a three-man crew and a top-mounted 140 mm XM291 powder cannon. In order to ensure adequate front protection despite the space requirement for the drive train , the hull front was inclined very sharply in order to increase the effective armor thickness. The driver was housed in the classic style in the front of the tub, the commander and rifleman should sit in the tower cage.

Stryker MGS with a 105mm cannon

The exact design of the loading machine is still subject to confidentiality, which leads to disinformation campaigns . For example, a report in the ARMOR magazine of the US armed forces depicted the tank with a full-fledged turret, or claims an ammunition carousel under the turret in addition to the tape loader in the rear of the hull, with no more space for the crew. The following solution, also shown in the magazine, is the most likely: In the rear of the hull there is a multi-storey tape loader that contains the ammunition supply. If the turret is in the 12 o'clock position, the tape loader can load a transfer piece with ammunition, which is located in the middle of the turret cage between the two soldiers. In the report, only two levers are shown, which seems nonsensical, an ammunition drum like the Stryker MGS is more likely. In any turret position, the drum can now turn so that the desired ammunition comes to a stop on the loading arm. For loading, the rear end of the cassette is raised and then pulled axially into the rear of the apex mount with the aid of a loading arm. There the front end of the cartridge pivots up to be in line with the barrel of the gun. Now the cartridge and the propellant charge are pushed into the chamber with a ram and the weapon is locked. The process is now reversed: the empty cassette tilts at the front and is then pushed axially into the drum by the loading arm, where the end of the cassette also swings away. The drum can now turn to the next cartridge and the cycle starts over.

The top mount of the Block III tank looks very similar to the Low Profile Turret of the Expeditionary Tank and the Stryker MGS , as all products are manufactured by GDLS. Presumably the same plans were used, as the M256 is compatible with the M68 cannon in the Abrams and the XM291 in turn had to cope with the installation dimensions of the M256. The Stryker Mobile Gun System uses a Meggitt Defense Systems ammunition drum with ten rounds instead of the tape loader in the rear of the hull. This can load the transfer drum when the tower is at 12 o'clock. The rest should be almost identical, except for the smaller ammunition.

ammunition

The 140 mm ammunition is about 1.5 meters long and divided into two parts. The cartridge has a length of about one meter and is equipped with a burning case with a transfer fuse at the end. The additional propellant charge is about half a meter long and equipped with a burnable case with a case stub made of steel, which contains the actual detonator. When pushed together, the two parts connect with a snap lock, which also enables the ignition charge to be transferred. The 140 mm ammunition can be fired from all NATO cannons of this caliber, such as the NPzK-140 from RGR Armament GmbH, as it was developed as part of the multinational FTMA program. The ammunition has already been standardized and given XM numbers:

XM964 APFSDS: Balancing ammunition , appeared at the same time as the M829A1. The structure should therefore be identical. The muzzle energy is around 23 MJ.

XM965 HEAT: Multi-purpose bullet with shaped charge and fragmentation jacket against semi-hard and soft targets.

XM966 Üb-Mun: Practice ammunition for both types of projectile.

The 120 mm ammunition is standardized according to STANAG 4385 . The 120 mm version can therefore fire the entire range of NATO ammunition of this caliber. These are exemplarily:

M829A3 APFSDS: Current US Army heavy ammunition . As with the 120 mm L / 55 from Rheinmetall, the gain in muzzle energy will be around + 15% compared to the L / 44.

M830 MPAT: A shaped charge multipurpose projectile for light ground targets and slow, low-flying aerial targets.

M865 KE-Ub: Practice ammunition for the bullet

photos

Individual evidence

^ African Armed Forces Journal: The Soviet FST-2 and the Russian T-95: The New Russian Tank Generation Coming into Focus. September 2010 ( page no longer available , search in web archives ) (PDF; 2.5 MB)@1@ 2

↑ ARMOR Magazine: The Resurrection of Russian Armor: Surprises from Siberia. Sept / Oct 1998 ( Memento from September 21, 2012 in the Internet Archive ) (PDF; 4.4 MB)

^ Defense Daily: Armored modernization needed to counter future Soviet tanks; LH procurement cost put at $ 35.2 billion for 1875 aircraft; Army decides to procure NLOS. April 26, 1990 ( Memento from December 19, 2015 in the Internet Archive )

↑ RM Orgorkiewicz: Future Tank Guns. Part I: solid and liquid propellant guns. Janes International Defense Review, 12/1990, p. 1377.

↑ Steven J. Zaloga, Peter Sarson: M1 Abrams Main Battle Tank 1982-92. ISBN 1855322838 .

↑ ARMOR Magazine: Autoloaders, Crew Size, and Ammunition Lethality. Nov./Dec. 1995 ( Memento from September 21, 2012 in the Internet Archive ) (PDF; 3.8 MB)

^ FAS: Electro Thermal Chemical Gun Technology Study. March 1999 ( Memento from September 20, 2012 in the Internet Archive ) (PDF; 922 kB)

↑ BAE Systems / ARDEC: Recent Activities in Electro-Thermal Chemical Launcher Technologies at BAE Systems. May 2006 ( Memento from April 8, 2013 in the Internet Archive )

^ Directory of Federal Laboratory and Technology Resources: A Guide to Services, Facilities and Expertise. Jan. 1993

↑ ^a ^b ^c ^d PROCEEDINGS OF THE SIXTH US ARMY SYMPOSIUM ON GUN DYNAMICS VOLUME I OF II May 1990 ( Memento from March 4, 2016 in the Internet Archive ) (PDF; 10.7 MB)

^ Hilmes, Rolf: Aspects of Future MBT Conception. Military Technology, June 30, 1999.

↑ US ARMY ARMAMENT RESEARCH, DEVELOPMENT AND ENGINEERING CENTER: EFFECT OF SHOT PEENING AND OVERLOAD RESIDUAL STRESSES ON EX35 MULTI-LUG BREECH FATIGUE LIFE. Sept. 1996 ( Memento from April 8, 2013 in the Internet Archive )

↑ ^a ^b ^c ^d Army Guide: ATAC ( Memento from July 6, 2012 in the Internet Archive )

^ Us Future Combat & Weapon Systems Handbook. 2011

↑ ARMY ARMAMENT RESEARCH DEVELOPMENT AND ENGINEERING CENTER: Experimental and Analytical Investigation of a Steel Pressure Vessel Overwrapped with Graphite Bismaleimide. May 1987