The AT4 (also AT-4) 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 AT4 is intended to give infantry units a means to destroy or disable armoured vehicles and fortifications, although it is generally ineffective against current modern main battle tanks (MBT). The launcher and projectile are manufactured prepacked and issued as a single unit of ammunition, with the launcher discarded after a single use.
The AT4 is a development of the 74-mm Pansarskott m/68 (Miniman), adopted by the Swedish Army in the late 1960s. Like the m/68, the AT4 was designed by Förenade Fabriksverken (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 anti-armor 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 armoured 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 far more accurate than previous individual antiarmor weapons against moving targets. Another key requirement was that the AT4 not only be able to penetrate armour, 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.
Even before the AT4 had been adopted by Sweden, it was entered into a US 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 US Viper (for baseline comparison purposes) and the Swedish AT4. The US 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, with the Armbrust coming in second.
Though very impressed with the simplicity and durability of the tested version of the AT4, the US 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 US Army as the Lightweight Multipurpose Weapon M136. 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 US Army version.
Due to the urban combat conditions that US military forces faced regularly during the Iraq War, the US Army Close Combat Systems manager in charge of purchases of the AT4 suspended orders for the standard version of the AT4 and US military forces are now only ordering the AT4 CS (Confined Space) version.
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 inertia 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, the disposable AT4 design greatly reduces manufacturing costs by using a reinforced smoothbore fiberglass outer tube. In a recoilless weapon, the barrel does not need to contend with the extreme pressures found in traditional guns and can thus be made very lightweight. This fact, combined with the almost complete lack of recoil, means that relatively large projectiles (comparable to those found in mortars and artillery systems) can be utilised, which would otherwise be impossible in a man-portable weapon.