AT4

The AT4 (also variously AT4 CS, AT4-CS, AT-4CS or just AT-4; an alpha-phonetic word play on the weapon's calibre of 84 mm[citation needed]; "CS" represents "Closed (or 'confined') Spaces" referring to the rocketry being designed to operate effectively from within buildings in an urban environment. ) is a portable one-shot anti-tank weapon built in Sweden by Saab Bofors Dynamics (previously Bofors Anti Armour Systems). In the U.S. and NATO inventory, it replaced the M72 LAW (Light Anti-armor Weapon). Saab has had considerable sales success with the AT4, making it one of the most common light anti-tank weapons in the world. 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, rather than as a weapon system, with the launcher discarded after a single use.




Development
The AT4 is a development of the 74 mm Pskott m/68 (Miniman), adopted by the Swedish army in 1960's. Like the m/68, the AT4 was designed by Försvarets Fabriksverk (FFV) and manufactured at their facility at Zakrisdal, Karlstad, Sweden.

Even before the AT4 had been adopted by Sweden, it participated in a competition for a new anti-tank weapon for the U.S. Army. Runners up were the AT4 and the German Armbrust. Though impressed with the AT4, the US Army saw room for improvement, specifically the sights and slings, which were redesigned. Thereafter, the AT4 was adopted by the U.S. Army as the M136. The Swedish army recognised these improvements and subsequently adopted the Americanized version of the AT4 as the Pansarskott m/86 (Pskott m/86).

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 (MBT). However, the project was canceled due to the dissolution of the Soviet Union and cuts in Western defense budgets.

Operation
The AT4 operates on the principle of a recoilless weapon, meaning that the forward inertia of the projectile is balanced by the mass of propellant gases ejecting from the rear of the barrel. Since the weapon generates almost no recoil, a relatively large projectile can be fired which would otherwise be impossible in a man-portable weapon. Additionally, the barrel can be designed to be very lightweight as it does not have to contend with the extreme pressures found in traditional guns. The disadvantage of this 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 user himself. This makes it difficult to employ in confined areas.

he problem of back blast has been mitigated recently 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.

To fire, the user must first ensure that no friendly troops or equipment are present in the back blast area. If firing from the prone position (i.e. lying on his stomach) he must also place his legs well to the side to avoid burning himself. He then disengages two safeties, cocks a mechanical firing pin and presses a trigger button. Aiming is accomplished via range-adjustable plastic sights, which are concealed beneath sliding covers for transport. Alternatively, the weapon can carry an optical night sight on a removable mount.

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 rocket. The 20mm version is also a recoilless weapon 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 (14.75 pounds)
Bore diameter: 84 mm
Maximum effective range: 300 metres (984.3 feet), although it has been used in excess of 500 meters for area fire.
Penetration: 400 mm of rolled homogeneous armour (RHA) (also see below)
Time of flight (to 250 metres): less than 1 second
Muzzle velocity: 285 metres (950 feet) per second
Operating temperature: -40 to +60°C (-40 to +140°F)
Ammunition: Fin-stabilized projectile with shaped charge warhead