AT4

The AT4 (also variously AT-4, AT4 CS, AT4-CS, or AT-4CS)^[6] is an 84-mm unguided, portable, single-shot recoilless smoothbore weapon built in Sweden by Saab Bofors Dynamics (previously Bofors Anti-Armour Systems). Saab has had considerable sales success with the AT4, making it one of the most common light anti-tank weapons in the world.

The designation "CS" represents "confined space" referring to the propellant charge being designed to operate effectively within buildings in an urban environment.^[7] It is intended to give infantry units a means to destroy or disable armored vehicles and fortifications, although it is not generally sufficient to defeat a modern main battle tank (MBT). The launcher and projectile are manufactured prepacked and issued as a single unit of ammunition with the launcher discarded after a single use.

Development

The AT4 is a development of the 84-mm Pansarskott m/68 ^[8] (Miniman), adopted by the Swedish Army in the late 1960s. Like the m/68, the AT4 was designed by Försvarets Fabriksverk (FFV) and manufactured at their facility at Zakrisdal, Karlstad, Sweden. FFV began research in a replacement for the m/68 in 1976, deliberately designing an individual antiarmor weapon that would not be able to defeat the heavy armour protection of MBTs (main battle tanks) in frontal engagements, believing that to be counterproductive. The AT4 was designed as a weapon to engage medium to light armored vehicles from any direction, MBTs from the sides or rear, and as an assault weapon against buildings and fortifications. FFV also had the design goal of a weapon that was simple to use, rugged and was far more accurate than previous individual antiarmor weapons against moving targets. Another key requirement was that the AT4 not only be able to penetrate armor, but also have a devastating beyond-armour effect after penetration. FFV and the Swedish Army began the first evaluation firings of the prototype AT4s in the spring of 1981 with 100 tested by early 1982.^[9]

Even before the AT4 had been adopted by Sweden, it was entered into a U.S. Army competition for a new anti-tank weapon mandated by Congress in 1982 when the FGR-17 Viper failed as a replacement for the M72 LAW. Six weapons were tested in 1983 by the US Army: the British LAW 80, the German Armbrust, the French APILAS, the Norwegian M72E4 (an upgraded M72 LAW), the U.S. Viper (for baseline comparison purposes) and the Swedish AT4. The U.S. Army reported to Congress in November 1983 that the FFV AT4 came the closest to meeting all the major requirements established to replace the M72 LAW,^[10] with the Armbrust coming in second.^[11]

Though very impressed with the simplicity and durability of the tested version of the AT4, the U.S. Army saw some room for improvement, specifically the addition of rear and front bumpers on the launch tube and changes to the sights and slings. After these changes, the AT4 was adopted by the U.S. Army as the Lightweight Multipurpose Weapon M136.^[12] The Swedish army also recognized these improvements and subsequently adopted the Americanized version of the AT4 as the Pansarskott m/86 (Pskott m/86), with the addition of a forward folding hand grip to help steady the AT4 when being aimed and fired. The forward folding grip is the only difference between the AT4 adopted by Sweden and the U.S. Army version.

Due to the urban combat conditions that US military forces in the last several years have been facing regularly, the US Army Close Combat Systems manager in charge of purchases of the AT4, suspended orders for the standard version of the AT4, and are now ordering only the AT4 CS version.^[13]

Operation

The AT4 may be considered a disposable, low cost alternative to a Carl Gustav recoilless rifle. The AT4 took many of its design features from the Carl Gustav, which operates on the principle of a recoilless weapon, where the forward inertia of the projectile is balanced by the mass of propellant gases ejecting from the rear of the barrel. But unlike the Carl Gustav, which uses a heavier and more expensive steel tube with rifling,^[14] the disposable AT4 design greatly reduces manufacturing costs by using a reinforced smoothbore fiberglass outer tube. Since recoilless weapons generate almost no recoil, a relatively large projectile can be fired which would otherwise be impossible in a man-portable weapon.

In the system originally developed by FFV for the Carl Gustav, a plastic blowout plug is placed at the center rear of the shell casing containing the projectile and propellant, which itself is enclosed in the AT4 outer tube. When the gases build up to the correct pressure level, the blowout plug disintegrates allowing the proper amount of gases to be vented to the rear, balancing the propellant gases pushing the projectile forward.

The AT4 uses a unique method developed earlier by FFV and adopted for the AT4: the spring-loaded firing rod is located down the side of the outer tube, with the firing pin at the rear side of the tube. When released, the firing pin strikes a primer located in the side of the casing's rim. Additionally, as the shell casing absorbs the majority of the firing stresses, the launch tube can be designed to be very lightweight as it does not have to contend with the extreme pressures found in traditional cannons.

The disadvantage of the recoilless design is that it creates a large back blast area behind the weapon which can cause severe burns and overpressure injuries both to friendly personnel in the vicinity of the user and sometimes to the users themselves, especially in confined spaces. The back blast may also reveal the user's position to the enemy.

The problem of back blast has been recently solved with the AT4-CS (Confined Space) version, specially designed for urban warfare. This version uses a saltwater countermass in the rear of the launcher to absorb the back blast; the resulting spray captures and dramatically slows down the pressure wave, allowing troops to fire from enclosed areas. It should be noted that the AT4-CS version also reduced its muzzle velocity from the original 290 mps to 220 mps as part of its effort to be user safe in a confined space, making the AT4-CS version less effective.

To fire, the gunner first removes the safety pin located at the rear of the tube, which unblocks the firing rod. He then takes a firing position ensuring that no one is present in the back blast area. If firing from the prone position (lying on his stomach) he must also place his legs well to the side to avoid burning himself. Then the gunner moves back the front and rear sight covers, allowing the sights to pop up into their firing positions. The AT4 sights are iron sights and were originally developed for the cancelled Viper, and are similar in concept and use to those on assault rifles.^[15] He then removes the first of two safeties by moving the firing rod cocking lever (located on the left side) forward and then over the top to the right side. The gunner takes aim, while at the same time holding down the red safety lever located in front of the cocking lever, and then fires by pressing forward the red firing button with his right thumb. Both the red safety lever and firing button must be pressed down at the same time to fire the AT4. The red firing button has resistance similar to the trigger pull of an assault rifle, so the gunner does not have to jab at the firing button which could throw his aim off.

After firing, the AT4 is discarded. Unlike the heavier Carl Gustav, the AT4 outer tube is built only to take the stress of one firing; it is not reusable and cannot be reloaded like the Carl Gustav.

The AT4 can mount an optical night sight on a removable fixture. In U.S. military use, the launcher can be fitted with the AN/PAQ-4C, AN/PEQ-2, or the AN/PAS-13 night sights.

The AT4 requires little training and is quite simple to use, making it suitable for general issue. However, as the cost of each launcher makes regular live-fire training very expensive, practice versions exist which are identical in operation but fire reloadable 9mm or 20mm tracer ammunition. Both practice cartridges are unique to their respective weapons, with their trajectory matched to that of the live round. The 20mm version also has a recoilless weapon effect with same high noise and back blast as the AT4 firing and is favored by the Swedish army because of the added realism of the back blast as compared to the "plonk" sound of the 9mm round (similar to the sound of a finger tapping on an empty can).

Specifications

• Length: 101.6 cm (40 in.)
• Weight: 6.7 kg (14.77 pounds)
• Bore diameter: 84 mm
• Maximum effective range: 300 metres (328 yards), although it has been used in excess of 500 meters (547 yards) for area fire.
• Penetration: 400 mm (15.7 inches) of rolled homogeneous armour (RHA) (also see below)
• Time of flight (to 250 metres, or 273 yards): less than 1 second
• Muzzle velocity: 285 metres (950 ft) per second
• Operating temperature: -40 to +60°C (-40 to +140°F)
• Ammunition: Fin-stabilized projectile with HEAT warhead

Projectiles

There are several different projectiles for the AT4. Note that since the AT4 is a one-shot weapon, these projectiles are preloaded into the launcher tubes.

HEDP 502 (High Explosive Dual Purpose)^[16]

For use against bunkers, buildings, enemy personnel in the open and light armor. The projectile can be set to detonate on impact or with a slight delayed detonation. The heavier nose cap allows the HEDP projectile to penetrate light walls or windows and then explode, or "skipped" off the ground for an air-burst. For use against light armor, there is a smaller cone HEAT warhead with 150 mm (5.9 inches) of penetration against RHA.

HP (High Penetration)

Extra high penetration ability (up to 500 mm (19.7 inches) to 600 mm (23.6 inches) of RHA.)

AST (Anti Structure Tandem-warheads)

Designed for urban warfare where a projectile heavier than the HEDP AT4 is needed. Two warheads, first one a HEAT with a shallow cone resulting in less penetration but a wider hole, and a second follow through high-blast warhead. It has two settings: one for destroying bunkers and one for mouse holing a building wall for combat entry.^[17]

HEAT (High Explosive Anti-Tank)

The AT4 HEAT can penetrate up to 420 mm (16.5 inches) of RHA with beyond-armour effect.^[18]

AT8 (Bunker Busting)

A version of the AT4 where the standard HEAT projectile is replaced with the bunker busting warhead developed for the SMAW. No orders placed.^[19]

AT12 (130mm Frontal Engagement Version)

In the early 1990s, there were tests of a tandem charge 130-mm version (Bofors AT 12) that would be able to penetrate the front armor of any modern main battle tank. However, the project was canceled due to the dissolution of the Soviet Union and cuts in Western defense budgets.

Users

•  Argentina: Argentine Marines.^[20]
•  Brazil^[21]
•  Croatia^[21]
•  Denmark: Designated PVV M/95 (Panserværnsvåben Model 1995).^[22]:93
•  Estonia^[23]
•  France: Designated ABL (Anti Blindé Léger) by the French Army.^[24]
•  Georgia^[21]
•  Iraq: American forces supplied the Iraqi military with AT4 weapons.^[25]
•  Ireland: Called the SRAAW (Short Range Anti Armour Weapon) by the Irish Defence Forces.^[22]:139
•  Kazakhstan^[21]
•  Kyrgyzstan^[21]
•  Latvia^[26]
•  Lebanon: Roughly 1,000 pieces purchased.^[27]
•  Lithuania: Lithuanian Armed Forces.^[28]
•  Netherlands^[29] (Replaced by Pzf-3)
•  Poland^[30]
•  Sweden: Designated Pansarskott m86.^[21]
•  Taiwan^[21]
•  Ukraine^[21]
•  United Kingdom: Small quantities of AT4 and HP projectiles purchased.^[2]
•  United States: Designated M136 AT4 in USMC and United States Army service, beginning in early 1987.^[31] The AT4 was used in the U.S. invasion of Panama, the Afghanistan War, the Gulf War, and the Iraq War.^[1] Over 300,000 have been built locally, under license by ATK.^[2]
•  Uzbekistan^[21]
•  Venezuela: The AT4 has been in the Venezuelan arsenal since the 1980s.^[21][32] In 2009, it was reported that AT4 weapons sold to Venezuela had been captured from FARC insurgents in Colombia, leading Colombia to accuse Venezuela of selling the weapons to the insurgents, and heightening tensions between the two countries.^[32][33]

See also

• Urban Assault Weapon
• LAW 80
• APILAS
• M141 Bunker Defeat Munition

References and notes

External links

• AT4 - Saab Bofors Dynamics video of various AT-4 versions
• AT4 Information Page - Modern Firearms
• Swedish article on AT4 translated to English
• M136 AT4 - Global Security
• AT4 article with early photos and press releases and ads
• U.S. Army field manual 3-23.25
• Brazilian newspaper recorded a AT-4 at Rocinha slum (translated to English)
• Official site for the AT4, covering the different versions of AT-4