Staff Writer (Updated: 10/6/2016):
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.