AS90 Braveheart is the latest 52 Calibre version of the British Army's 155mm AS90 Self-propelled Howitzer. Designated 'NATO's Sledgehammer' during the Kosovo conflict, AS90 played a prominent and effective role for the Coalition Forces in the 2003 Gulf War.

Designed to offer in-built stretch potential, AS90 is undergoing a phased development programme with the British Army. Recognising the superiority of AS90 Braveheart over competing equipments, Poland awarded a contract for the system to replace obsolete 122mm and 152 calibre artillery. Braveheart has also been leased to Sweden where it is undergoing extensive trials.

In service with the British Army in the UK, Germany, Bosnia, Kosovo and Iraq and successfully trialled in Kuwait, Saudi Arabia, Jordan, India, Norway, Finland, Poland, Canada and the United States, AS90 Braveheart has an unrivalled pedigree.

The AS90 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 turret 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 air sentry hatch.

The magazine is in the rear of the turret and holds 31 155 mm projectiles. It incorporates simple indexing mechanisms that 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 12 at the front left and centre right of the turret. Additional 155 mm ammunition can be stowed in the lower part of the turret compartment taking the stowage capacity to over 40 complete rounds.

A shell replenishment aid 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 replenishment aid 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 gun-layer at the forward right, commander behind and the two loaders on the left. If required, the turret can be operated with a crew of just two.

The design of the ordnance, cradle and saddle is such that the 155 mm 39 calibre barrel can be easily withdrawn from the front of the turret, leaving the breech in place.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 other turret-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 BAE Systems Land Systems 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 MoU governing the standardisation of 155 mm ordnance and ammunition between France, 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 operate in both manual and semi-automatic modes and in the latter case the run-out energy is used to open the breech. Both German DM191 and US M82 percussion igniter tubes can be used.

The breech is connected to the barrel by a conventional interrupted screw thread. The 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 towed FH-70 155 mm field howitzer and the towed M198 155 mm howitzer 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°. Over 150 projectiles were fired during trials in the UK and these have shown that the Russian T-72 series chassis is a very stable firing platform and 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 under 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 either stowed 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 BAE Systems Automatic Gun Laying System (AGLS) provides the facilities automatically to lay the gun and 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 gunlayer's 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 gunlaying and burst rates of fire enable the AS90/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 Thales Land & Joint Systems 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 gunlayer has a two-axis joystick, simple aiming of the armament can be achieved quickly.

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 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 base of the turret.

A number of readily available growth options can be provided for the AS90 Turret. These include:

• a 155 mm 52 calibre barrel which increases the maximum range of conventional ammunition to 30,000 m and extended-range ammunition to 40,000 m. The 155 mm 52 calibre ordnance has already been tested in a British Army AS90

• onboard ballistic computation

• Shell Transfer Arm (STA)

• barrel cooling