M1 Abrams

The M1 Abrams is a main battle tank produced in the United States. The M1 is named after General Creighton Abrams, former Army Chief of Staff and Commander of US military forces in Vietnam from 1968 to 1972. It is a well armed, heavily armored, and highly mobile tank designed for modern armored ground warfare. Notable features of the M1 Abrams include the use of a powerful gas turbine engine, the adoption of sophisticated composite armor, and separate ammunition storage in a blow-out compartment for crew safety. It is one of the heaviest tanks in service, weighing in at close to 70 short tons.

The M1 Abrams entered U.S. service in 1980, replacing the 105 mm gun, full tracked M60 Patton main battle tank. It did, however, serve for over a decade alongside the improved M60A3, which had entered service in 1978. Three main versions of the M1 Abrams have been deployed, the M1, M1A1, and M1A2, incorporating improved armament, protection and electronics. These improvements, as well as periodic upgrades to older tanks have allowed this long-serving vehicle to remain in front-line service. It is the principal main battle tank of the United States Army and Marine Corps, and the armies of Egypt, Kuwait, Saudi Arabia, and since 2007, Australia.

Background
The first attempt to replace the aging M60 series of tanks was the abortive MBT-70, developed in partnership with West Germany. The M60 was itself a gradual evolution of a design starting with the World War II era M26 Pershing, with a very tall profile, and average armor and weaponry compared to the contemporary Soviet designs. The MBT-70 was very ambitious, like many American weapons programs of the 1960s. It had a gun launched missile system, kneeling suspension, a driver housed in the turret, and various other ideas that ultimately proved unsuccessful. Cancellation of this project paved the way for the much more successful M1 Abrams tank, which did not incorporate most of the troublesome innovations tried by the MBT-70.

Development
The XM1 Abrams was designed by Chrysler Defense (in 1979, General Dynamics Land Systems Division purchased Chrysler Defense Division) and is currently produced by General Dynamics Corporation in Lima, Ohio, and first entered US Army service in 1980. It was armed with the license-built version of the 105 mm Royal Ordnance L7 gun.

An improved version of the M1, the M1A1, was introduced in 1985. The M1A1 has the M256 120 mm smoothbore cannon developed by Rheinmetall AG of Germany for the Leopard 2, improved armor, and a CBRN protection system. The M1A2 is a further improvement of the M1A1 with a commander's independent thermal viewer and weapon station, position navigation equipment, digital data bus and a radio interface unit. The M1A2 SEP (System Enhancement Package) added digital maps, FBCB2 (Force XXI Battlefield Command Brigade and Below) capabilities, and an improved cooling system to maintain crew compartment temperature with the addition of multiple computer systems to the M1A2 tank.

Further upgrades include depleted uranium armor for all variants, a system overhaul that returns all A1s to like-new condition (M1A1 AIM), a digital enhancement package for the A1 (M1A1D), a commonality program to standardize parts between the U.S. Army and the Marine Corps (M1A1HC) and an electronic upgrade for the A2 (M1A2 SEP).

During Operations Desert Shield and Desert Storm and for Bosnia, some M1A1s were modified with armor upgrades. The M1 can be equipped with mine plow and mine roller attachments if needed. The M1 chassis also serves as a basis for the Grizzly combat engineering vehicle and the M104 Wolverine heavy assault bridge.

Over 8,800 M1 and M1A1 tanks have been produced at a cost of US$2.35–$4.30 million per unit, depending on the variant.

Design features
Armor
The Abrams is protected by the British designed 'Chobham armor', a further development of the British 'Burlington' armor. Chobham is a composite armor formed by spacing multiple layers of various alloys of steel, ceramics, plastic composites, and kevlar, giving an estimated maximum (frontal turret) 1320-1620 millimeters of RHAe versus HEAT (and other chemical energy rounds) and 940–960 mm versus kinetic energy penetrators. It may also be fitted with reactive armor over the track skirts if needed (as in the Urban Survival Kit) and Slat armor over the rear of the tank and rear fuel cells to protect against ATGMs. Fuel and ammunition are in armored compartments with blowout panels to protect the crew from the risk of the tank's own ammunition cooking off if the tank is damaged. Protection against spalling is provided by a kevlar liner. Beginning in 1987, M1A1 tanks received improved armor packages that incorporated depleted uranium (DU) mesh in their armor at the front of the turret and the front of the hull. Armor reinforced in this manner offers significantly increased resistance towards all types of anti-tank weaponry, but at the expense of adding considerable weight to the tank, as depleted uranium is 1.7 times denser than lead. The first M1A1 tanks to receive this upgrade were tanks stationed in Germany, since they were the first line of defense against the Soviet Union. US-based tank battalions participating in Operation Desert Storm received an emergency program to upgrade their tanks with depleted uranium armor immediately before the onset of the campaign. M1A2 tanks uniformly incorporate depleted uranium armor, and all M1A1 tanks in active service have been upgraded to this standard as well, the armor thickness is believed to be equivalent to 24 inches (610 mm) of RHA. The strength of the armor is estimated to be about the same as similar western, contemporary main battle tanks such as the Leopard 2. In the Persian Gulf War, Abrams tanks survived multiple hits at relatively close ranges from Iraqi Lion of Babylon tanks and ATGMs. M829A1 "Silver Bullet" APFSDS rounds from other M1A1 Abrams were unable to penetrate the front and side armor (even at close ranges) in friendly fire incidents as well as an incident in which another Abrams tried to destroy an Abrams that got stuck in mud and had to be abandoned.

In addition to the advanced armor, some Abrams, are equipped with a Missile Countermeasure Device that can impede the function of guidance systems of semiactive control line-of-sight (SACLOS) wire and radio guided anti-tank missiles (Russian AT-3, AT-4, AT-5, AT-6 and the like) and thermally and infrared guided missiles (ATGM). This device is mounted on the turret roof in front of the Loader's hatch, and can lead some people to mistake Abrams fitted with these devices for the M1A2 version, since the Commander's Independent Thermal Viewer on the latter is mounted in the same place, though the MCD is box-shaped and fixed in place as opposed to cylindrical and rotating like the CITV.

In the chance that the Abrams does suffer damage resulting in a fire in the crew compartment, the tank is equipped with a halon fire-suppression system that automatically engages and extinguishes fires in seconds.

Armament
Main armament
M68A1 rifled gun
The main armament of the original model M1 was the M68A1 105 mm rifled tank gun firing a variety of high explosive anti-tank (HEAT), high explosive, white phosphorus and an anti-personnel (multiple flechette) round. This gun is a license-built version of the British Royal Ordnance L7 gun. While being a reliable weapon and widely used by many NATO nations, a cannon with lethality beyond the 3 kilometer range was needed to combat newer armor technologies. To attain that lethality, projectile diameter needed to be increased. The M68A1's performance in terms of accuracy and armor-piercing penetration is on par with the M256A1 up to 3 kilometers out, but beyond that range the 105 mm projectile lacks the kinetic energy to defeat modern armor packages.

he main armament of the M1A1 and M1A2 is the M256A1 120 mm smoothbore gun, designed by Rheinmetall AG of Germany, manufactured under license in the United States by Watervliet Arsenal, New York. The M256A1 is a variant of the Rheinmetall 120 mm L/44 gun carried on the German Leopard 2 on all variants up to the Leopard 2A5. Leopard 2A6 replaced the L/44 barrel with a longer L/55.

The M256A1 fires a variety of rounds. The M829A2 was developed specifically to address the threats posed by a Soviet T-90 or T-80U tank equipped with kontakt-5 Explosive Reactive Armor. It also fires HEAT shaped charge rounds such as the M830, the latest version of which (M830A1) incorporates a sophisticated multi-mode electronic sensing fuse and more fragmentation which allows it to be used effectively against armored vehicles, personnel, and low-flying aircraft. The Abrams uses a manual loader, due to the belief that having a crewman reload the gun is faster and more reliable.[citation needed] and because autoloaders do not allow for separate ammunition storage in the turret.[citation needed]

The new M1028 120 mm anti-personnel canister cartridge was brought into service early for use in the aftermath of the 2003 invasion of Iraq. It contains 1,098 3/8 inch tungsten balls which spread from the muzzle to produce a shotgun effect lethal out to 600 m. The tungsten balls can be used to clear enemy dismounts, break up hasty ambush sites in urban areas, clear defiles, stop infantry attacks and counter-attacks and support friendly infantry assaults by providing covering fire. The canister round is also a highly effective breaching round and can level cinder block walls and knock man-sized holes in reinforced concrete walls for infantry raids at distances up to 75 meters.

In addition to this, the new XM1111 (Mid-Range-Munition Kinetic Energy) is also in development. Essentially a cannon-fired guided round, it has a range of roughly 12 km and uses a KE warhead which is rocket assisted in its final phase of flight. This is intended to be the best penetrator yet, an improvement over the US 3rd generation DU penetrator (estimated penetration 790 mm).

Secondary armament
The Abrams tank has three machine guns:
A .50 cal. (12.7 mm) M2 machine gun in front of the commander's hatch. On the M1, M1IP and M1A1, this gun is on a powered mount and can be fired using a 3× magnification sight, known as the Commander's Weapon Station (CWS for short), while the vehicle is "buttoned up" with all its hatches closed to protect the crew. On the M1A2 & M1A2SEP, this gun is on a flex mount (seen at right), the Commander having to expose himself to fire the weapon manually. With the forthcoming TUSK addon kit, an M2 or an Mk 19 grenade launcher can be mounted on the CROWS remote weapons platform (similar to the Protector M151 remote weapon station used on the Stryker family of vehicles). The upgrade variant called M1A1 Abrams Integrated Management (AIM) equips the .50 caliber gun with a thermal sight for accurate night and other low-visibility shooting.

A 7.62 mm M240 machine gun in front of the loader's hatch on a skate mount. Some of these have been fitted with gun shields during the ongoing conflict in Iraq as seen in the image at right, as well as night-vision scopes for low-visibility engagements.

A second 7.62 mm M240 machine gun in a coaxial mount to the right of the main gun. The coaxial MG is aimed and fired with the same computer fire control system used for the main gun.
(Optional) A second 12.7 mm M2 machine gun can be mounted directly above the main gun in a remote weapons platform as part of the TUSK upgrade kit mentioned below.

The turret is fitted with two six-barreled smoke grenade launchers (USMC M1A1s use an eight-barreled version). These can create a thick smoke that blocks both vision and thermal imaging, and can also be armed with chaff. The engine is also equipped with a smoke generator that is triggered by the driver. When activated, fuel is sprayed on the engine manifold, creating the thick smoke. However, due to change from diesel as a primary fuel to the use of JP-8, this system is disabled on most Abrams today, because JP-8 causes the tanks to catch fire when sprayed on the manifold. For the US Army in previous years, the Abrams usually maintained the provision for storing an M16 rifle or M4 carbine inside the turret in case the crew is required to leave the tank under potentially hostile conditions; while the crewmen were supplied with the M9 Beretta pistol as a personal sidearm. Considering the current (often dismounted) role of American armored crewmen and contemporary operating environments, though, current US Army crews maintain a rifle or carbine for each crewman. During Iraqi Freedom some crews were also issued M136 AT4 shoulder-fired anti-tank weapons under the assumption that they might have to engage heavy armor in tight urban areas where the main gun could not be brought to bear.

Aiming
The Abrams is equipped with a ballistic fire-control computer that uses data from a variety of sources, including the thermal or daylight Gunner's Primary Sight (GPS), all computing and displaying one of three components of the ballistic solution - lead angle, ammunition type, and range to the target. These three components are determined using a laser rangefinder, crosswind sensor, a pendulum static cant sensor, data on the ammunition type, tank-specific boresight alignment data, ammunition temperature, air temperature, barometric pressure, a muzzle reference sensor (MRS) that determines and compensates for barrel droop at the muzzle due to gravitational pull and barrel heating due to firing or sunlight, and target speed determined by tracking rate tachometers in the Gunner's or Commander's Controls Handles allowing for target speed input into the ballistic solution. The fire-control system uses these data to compute a firing solution for the gunner. The ballistic solution generated ensures a hit percentage greater than 95 percent at nominal ranges. Either the commander or gunner can fire the main gun. Additionally, the Commander's Independent Thermal Viewer (CITV) on the M1A2 can be used to locate targets and pass them on for the gunner to engage while the commander scans for new targets. In the event of a malfunction or damage to the primary sight system, the main and coaxial weapons can be manually aimed using a telescopic scope boresighted to the main gun known as the Gunner's Auxiliary Sight (GAS). The GAS has two interchangeable reticles; one for HEAT and MPAT (MultiPurpose AntiTank) rounds and one for APFSDS and STAFF (Smart Target-Activated Fire and Forget) ammunition. Turret traverse and main gun elevation can be accomplished with manual handles and cranks in the event of a Fire Control System or Hydraulic System failure. The commander's M2 .50 caliber machine gun on the M1 and M1A1 is aimed by a 3x magnification sight incorporated into the Commander's Weapon Station (CWS), while the M1A2 uses either the machine gun's own iron sights, or a remote aiming system such as the CROWS system when used as part of the TUSK (Tank Urban Survival Kit). The loader's M240 machine gun is aimed either with the built-in iron sights or with a thermal scope mounted on the machine gun.

Mobility
The M1 Abrams is powered by a 1500 hp (1119 kW) Honeywell AGT 1500 (originally made by Lycoming) gas turbine, and a six speed (four forward, two reverse) Allison X-1100-3B Hydro-Kinetic automatic transmission, giving it a governed top speed of 45 mph (72 km/h) on paved roads, and 30 mph (48 km/h) cross-country. With the engine governor removed, speeds of around 60 mph (97 km/h) are possible on an improved surface; however, damage to the drive train (especially to the tracks) and an increased risk of injuries to the crew can occur at speeds above 45 mph (72 km/h). The tank for all intents and purposes was built around this engine. The tank can be fueled with diesel fuel, kerosene, any grade of motor gasoline, JP-4 jet fuel, or JP-8 jet fuel; the US Army uses JP-8 jet fuel in order to simplify logistics. The Royal Australian Armoured Corps' M1A1 AIM SA uses diesel fuel; it is cheaper and makes practical sense for Australian military logistics. The gas turbine propulsion system has proven quite reliable in practice and combat, but its high fuel consumption is a serious logistic issue (starting up the turbine alone consumes nearly 10 gallons of fuel). The engine burns more than 1 gallon per mile and 12 gallons per hour when idle. The high speed, high temperature jet blast emitted from the rear of M1 Abrams tanks makes it difficult for the infantry to proceed shadowing the tank in urban combat. The turbine is very quiet when compared to diesel engines of similar power output and produces a significantly different sound from a contemporary diesel tank engine, reducing the audible distance of the sound, thus earning the Abrams the nickname, "whispering death" during its first REFORGER exercise. Honeywell was developing another gas turbine engine with General Electric for the XM2001 Crusader program that was also to be a replacement for the AGT-1500 engine already in the Abrams tank. The new LV100-5 engine is lighter and smaller (43% fewer parts) with rapid acceleration, quieter running and no visible exhaust. It also features a 33% reduction in fuel consumption (50% less when idle) and near drop-in replacement. The Abrams-Crusader Common Engine Program was shelved when the Crusader program was canceled, however Phase 2 of Army's PROSE (Partnership for Reduced O&S Costs, Engine) program calls for further development of the LV100-5 and replacement of the current AGT-1500 engine. Future US tanks may return to reciprocating engines for propulsion, as 4-stroke diesel engines have proven quite successful in other modern heavy tanks, e.g. the Leopard 2, Challenger 2 and Merkava.

The Abrams can be carried by a C-5 Galaxy or a C-17 Globemaster III. The limited capacity (two combat-ready in a C-5, one combat-ready tank in a C-17) caused serious logistical problems when deploying the tanks for the First Gulf War, though there was enough time for 1,848 tanks to be transported by ship.

Combat history
As the Abrams entered service in the 1980s, they would operate alongside M60A3 within the United States military, and with other NATO tanks in numerous Cold War exercises. These exercises usually took place in Western Europe, especially West Germany, but also in some other countries like South Korea. During such training, Abrams crews honed their skills for use against the men and equipment of the Soviet Union. However, by 1991 the USSR had collapsed and the Abrams would have its trial by fire in the Middle East.

Operation Desert Storm
The Abrams remained untested in combat until the Gulf War in 1991. A total of 1,848 M1A1s were deployed to Saudi Arabia. The M1A1 was superior to Iraq's Soviet-era T-55 and T-62 tanks, as well as Iraqi assembled Russian T-72s, and locally-produced copies (Asad Babil tank). The T-72s like most Soviet export designs lacked night vision systems and then-modern rangefinders, though they did have some night fighting tanks with older active infrared systems or floodlights—just not the latest starlight scopes and passive infrared scopes as on the Abrams. Only 23 M1A1s were taken out of service in the Gulf and one of these losses resulted in crew deaths from Iraqi fire. Some others took minor combat damage, with little effect on their operational readiness. Very few Abrams tanks were hit by enemy fire, and there was only one fatality, along with a handful of woundings as a result.

The M1A1 was capable of making kills at ranges in excess of 2,500 m. This range was crucial in combat against tanks of Soviet design in Desert Storm, as the effective range of the main gun in the Soviet/Iraqi tanks was less than 2,000 meters (Iraqi tanks could not fire anti-tank missiles like their Russian counterparts). This meant Abrams tanks could hit Iraqi tanks before the enemy got in range—a decisive advantage in this kind of combat. In friendly fire incidents, the front armor and fore side turret armor survived direct APFSDS hits from other M1A1s. This was not the case for the side armor of the hull and the rear armor of the turret, as both areas were penetrated at least in two occasions by friendly DU ammunition during the Battle of Norfolk.