The AS90 Universal Turret has been developed as a private venture by Marconi Marine, Land and Naval Systems (previously Vickers Shipbuilding and Engineering Limited) from the turret system used for the AS90 self-propelled artillery system which is now in service with the British Royal Artillery as its only self-propelled gun system.

The autonomous AS90 Universal Turret was first shown in 1993 and has been successfully trialled on a T-72 MBT chassis. Further firing, mobility and reliability trials took place in 1994 and a small number of improvements have been incorporated as a result of these trials.

In 1995, the AS90/T-72 combination underwent a system evaluation in India alongside three other competing systems.

A modified version of this turret with a 155 mm 52 calibre ordnance, is being offered to Poland to meet its future self-propelled artillery requirement. This would be installed on a locally developed chassis using T-72 automotive components.

The AS90 Universal Turret is of all-welded steel armour construction that provides protection against both small arms fire and shell splinters.

Access to the turret is via a hatch in the left side, the commander's cupola on the right side of the roof and the air sentry hatch on the left side of the turret roof. A 7.62 or 12.7 mm machine gun is mounted on the latter.

The magazine is in the rear of the turret and stows 31 projectiles; it incorporates simple indexing mechanisms which transfer the projectiles to a central point from where they are transferred to the loading tray.

The sealed containers mounted above the shell magazine house 21 propellant charges with a further 11 at the front left of the turret. Additional ammunition can be stowed in the carrier chassis so taking the stowage capacity to over 40 complete rounds.

A shell transfer arm was fitted for the Indian trials and this allows projectiles to be transferred from outside straight into the turret. The projectiles are loaded onto the shell transfer arm manually with the charges also being loaded manually through an opening in the turret rear on the left.

The turret has a standard crew of four with the gunlayer at the forward right, commander behind and the two loaders on the left. If required the turret can be operated by a crew of two.

The design of the ordnance, cradle and saddle is such that the 155 mm 39 calibre can be easily withdrawn from the front of the turret, leaving the breech in place.

In addition, the whole of the elevating mass, complete with saddle, can be quickly removed from the turret leaving all otherturret-mounted equipment intact.

The recoil system has two diametrically opposed buffers and one recuperator, each with its own integral reservoir to reduce external piping and space requirements. The system is protected by an easily removed armoured cover.

The ordnance is a Royal Ordnance Nottingham 155 mm 39 calibre barrel fitted with a vertical sliding split-block breech mechanism ensuring positive obturation. This is fitted with a double-baffle muzzle brake and a fume extractor. When travelling, the ordnance is held in an A-type travelling lock that is pivoted on the front of the hull.

The 155 mm 39 calibre ordnance conforms to the Quadrilateral Ballistic Agreement governing the standardisation of 155 mm ordnance and ammunition between Germany, Italy, UK and USA.

The unique design of self-obturation breech mechanism combines the rapid action of a sliding breech block with a Crossley pad obturator to provide a positive seal.

The breech can be operated in both manual and semi-automatic modes and, in the latter case, the runout energy is used to open the breech. Both the German DM191 and US M82 percussion igniter tubes can be used.

The breech is connected to the barrel by conventional interrupted screw thread. The 155 mm barrel is machined from an Electro-Slag Refined (ESR) forging of monobloc construction and is autofrettaged.

The system can fire the full range of ammunition used for the 155 mm field howitzer FH-70 and the 155 mm howitzer M198 to a range of 24,700 m with standard projectiles and to 30,000 m with base bleed projectiles.

Turret traverse is powered through a full 360° with weapon elevation from -5 to +70°. Extensive firing trials in India and the UK have shown that the T-72 is a very stable firing platform and that no spades are required.

To enable a rapid burst rate of fire to be achieved and a high rate of continuous fire to be sustained, an autoloader has been incorporated at the rear of the elevating mass.

This system provides a burst rate of fire of three rounds in 10 seconds and an intense rate of 18 rounds in less than 2 minutes. The equipment comprises a loading tray and power rammer for loading the projectiles with the propellant charges being loaded manually.

Ammunition replenishment is through the rear of the turret. Projectiles are loaded directly into the magazine and tray where they can be stowed either in the magazine or loaded through to the gun for firing. Power for the autoloader is provided by a small hydraulic power pack installed in the front left corner of the turret.

A Marconi Marine, Land and Naval Systems - designed Automatic Gun Laying System (AGLS) also track the vehicle's position. These two functions are achieved by an inertial navigation system which is fully integrated with the turret electrical system.

The inertial navigation system provides the accurate position and attitude of the gun and also the position of the vehicle, thus alleviating the prerequisite of surveying the firing position.

The required gun aiming orders are entered on the gun's layer display unit and fed to the turret control computer where a demand signal is generated to drive the elevation and traverse power amplifiers to lay the gun.

The layer's display unit shows gun azimuth and quadrant elevation and the target bearing and elevation together with the difference between the two. Target data can be entered directly from the layer's keypad or received from a fire-control system.

Trials have shown that the onboard navigation system combined with the automatic gun laying and burst rates of fire enable the AS90 Universal Turret/ T-72 to come into action, fire 18 rounds and move off again in less than 5 minutes.

For direct fire against targets up to 2,000 m away a day/night sight is mounted on the elevating mass adjacent to the layer. The graticule is calibrated for range and crossing target velocity and since the gun layer has a two-axis joystick, simple aiming of the armament can be quickly achieved.

The power supply for all the turret services is provided by a turret-mounted battery pack which is charged by an Auxiliary Power Unit (APU) mounted on the rear of the turret. The APU is based on a Honda diesel which is already manufactured in India.

This APU obviates the need to run the vehicle's main engine during fire missions and so helps to conserve fuel. A ventilation unit is fitted as standard to provide adequate air circulation for the crew.

The T-72 chassis can lay its own smoke-screen by injecting diesel fuel into the exhaust outlet on the left side of the hull. In addition, there is a bank of five electrically operated smoke grenade dischargers either side of the turret. Extensive external stowage for personnel kit is provided on the turret sides and between the top of the hull and the base of the turret.

Although the prototype AS90 Universal Turret has a 155 mm 39 calibre barrel, a number of other growth options are possible, these include:

• a 155 mm 52 calibre barrel which increases the maximum range of conventional ammunition to 30,000 m and that of extended range ammunition to 40,000 m. The 155 mm 52 calibre ordnance has already been tested in a British Army ASM and will be fitted as part of a mid-life upgrade. During the trials that took place in India in 1995,a 155 mm 52 calibre Royal Ordnance barrel was fitted and achieved a range in excess of 40,000 m

• onboard ballistic computation

• Shell Transfer Arm (STA)

• barrel cooling.

Development complete. Ready for production.