The AS90 currently serves as the backbone of British self-propelled artillery regiments. Such weapon systems supply the modern land army with a powerful "reach" across miles of terrain and provide accurate results through lethal ammunition types available. Since its inception in the early 1990s, the AS90 has been called to arms in a variety of theaters where the Royal Army has operated. The vehicle continues to provide valuable service even today and has undergone upgrade measures to keep her a viable gunnery platform into the next decade. The "AS90" designation stems from the wording of "Artillery System, 1990".
The original SP70 project of the 1970s sought to provide participating nations with a fully-modern, highly-capable self-propelled gun system to fit a universal NATO 155mm 39 caliber standard. The joint venture included the United Kingdom, Germany and Italy and was formally born in 1973 with the British firm of Vickers Shipbuilding and Engineering developing the turret (designated GBT155). In trials, the SP70 was outgunned in several respects by the competing American-made, proven and readily available M109 self-propelled gun which eventually led to the SP70 project being cancelled in full.
In an effort to shore up the inherent deficiencies in the abandoned SP70 design, Vickers took to creating an all-new private venture self-propelled artillery design that included both an in-house turret and chassis. The main gun itself was based on the 155mm FH70 towed field gun and several automotive components of the Challenger Main Battle Tank were integrated into the hull including a quick-change transmission system (removal in about 1 hour). The first prototypes were completed in 1986. After trials, the new Vickers product was formally adopted by the British Royal Army as the "AS90" (or "AS-90", known more formally as the "Gun Equipment 155mm L131") in 1989 to replace all existing heavy gun systems. First deliveries of the vehicle began in 1992 and some 179 examples were produced until 1995. In 1993, BAe Systems acquired Vickers Shipbuilding and went on to manage the AS90 family for the British Army. The AS-90 replaced the Abbot and M109 self-propelled artillery guns in British Army service and has also covered functions of the towed FH-70 gun system.
Outwardly, design of the AS90 is conventional by modern self-propelled gun standards. The hull is traditional in layout and sports six rubber-tired road wheels to a track side (each road wheel is doubled). The drive sprocket is fitted to the front of the track system (as is the engine) with the track idler at the rear and three track return rollers across the top. The hull sides are vertical panels though the glacis plate is well sloped, nearly horizontal. The boxy turret emplacement is set well to the rear of the hull with the forward-set engine balancing the vehicle's weight. The turret itself features slightly sloped side and front surfaces with entry/exit hatches located along the turret roof panel. "Pioneer" equipment can be stocked along the turret sides. A large access door at the extreme rear center of the vehicle hull allows for entry/exit of the crew and resupply of the 155mm projectiles from an ammunition carrier (the Foden DROPS 8x8 logistical vehicle). The main gun sits at the front center of the turret with its integrated recoil system very noticeable at the gun base. The gun tapers towards the muzzle end and a fume extractor is identified at the midway point of the barrel. The muzzle is capped by a conical double-baffled muzzle brake to content with the inherently violent recoil of such a heavy caliber weapon. The overall AS90 system weighs in at 45 tons. Passive night vision equipment is standard for the crew and hydropneumatic suspension (Hydrogas) for the road wheels allows for strong on road/off road capabilities.
The AS90 is crewed by five standard operating personnel. The driver sits at the front left side of the hull with the engine to his right. The engine consists of a single Cummins VTA 903T 660T-660 V8 turbo diesel, liquid-cooled engine delivering up to 660 horsepower at 2,800rpm. This supplies the vehicle with a top speed of 55 kilometers per hour and a range of370 kilometers. The remaining crew consists of the vehicle commander, a gunner (also known as the gun layer) and ammunition handlers. At least 48 x 155mm L15 series projectiles are carried aboard each vehicle system and 31 of these are within reach of the turret personnel. Self-defense (against both infantry and low-flying aircraft) is handled by a single fitting of an optional 7.62 general purpose or 12.7mm heavy machine gun on the turret roof - 1,000 rounds of ammunition are afforded to this weapon. Armor protection for the crew is relatively light by being only 17mm of steel at its thickest point. Construction is of welded steel for both turret and hull. A Nuclear, Biological and Chemical (NBC) system is also standard for the crew - harkening back to the days of the Cold War. 10 x smoke grenade dischargers can be called upon to cover offensive and retreat actions of the vehicle. An internal fire suppression system helps protect the crew from internal fires.
The main gun is cleared for the firing of 155mm projectiles and has an inherent range out to 25 kilometers. The 155mm L31/39 caliber ordnance version can strike at target areas out to 25 (24.7) kilometers while the 155mm/52 caliber version can reach out to 30 kilometers. Extended Range Ammunition (ERA) can further this value up to 80 kilometers. The standard gun projectile is a High-Explosive, Fragmentation (HE-FRAG) round and rocket-assisted types are available for increased ranges. The loader places the projectile onto the awaiting cradle arm which then automatically slides the round into the breech. The main gun is optimized with a split sliding breech mechanism which, when coupled with a capable crew, can fire up to 6 rounds per minute for up to three minutes if need be with sustained firing dropping to 2 rounds per minute. The turret sports a fully automatic gun laying system that displays pertinent information back to the vehicle commander, gunner and loader. The gun laying system is integrated with the vehicle's inertial navigation system known as the Dynamic Reference Unit (DRU). When traveling, the barrel is secured to a heavy duty "A frame" type clamp that folds out from the glacis plate. The turret emplacement offers up complete 360-degree traversal allowing the hull to point in any direction regardless of which direction the gun itself will fire in. Elevation is limited to +70 and -5 degrees. An auxiliary power unit allows the vehicle's engine to be powered down but keeps the turret functions active.
The original AS90 was converted for operations in desert environments to produce the "AS90D" designation ("D" = "Desert"). To content with the extreme temperatures and unforgiving climates inherent in such regions of the world (particularly in the Middle East), the engine received additional cooling measures to prevent overheating. Thermal protection was applied for the crew within and specially designed tracks were integrated into the design to promote much improved travel over loose sandy terrain.
In 2002, there proved a new initiative to increase the AS90's main gun reach on at least 96 of the existing AS90 vehicles with the addition of the longer 155mm/52 gun utilizing a specialized propellant charge. However, this project came to naught when the needed charge could not be agreed upon. These AS-90 systems would have been known as "AS90 Braveheart" after the upgrade. The Polish "Krab" self-propelled gun platform utilizes the turret system of the abandoned British AS90 "Braveheart" proposed vehicles but seats these on the hull of a Russian T-72 main battle tank. The completed designs are entirely indigenous to the Polish nation with the turrets procured through licensing. As such, existing British Army AS90 systems still field their original L31/39 caliber ordnance main guns. In 2008, the AS90 family had their electronics upgraded to modern standards.
AS90 units have been fielded in the Bosnian and Iraqi theaters of war in support of British and coalition army actions. The system staffs the inventory of no fewer than six British Army field artillery regiments (Royal Horse Artillery and Royal Artillery).