From 1989, NORICUM manufactured an improved version of the 155 mm SRC International GC 45 155 mm gun-howitzer (see entry under Belgium in this section), under the designation GH N-45 (Gun-Howitzer, NORICUM, 45 calibre). A total of 12 of the original GC 45 systems were provided to the Royal Thai Marines.

NORICUM assembled all but two of the 12 guns (two six-gun batteries) supplied to the Royal Thai Marines and then began deliveries of over 600 guns to various customers.

In June 1987, the Thai Cabinet approved a purchase of six GH N-45 weapons at a cost of USD7 million, all of which have now been delivered. These models are fitted with an auxiliary power unit.

In 1994, the Swiss-based company T & T Technology Trading Ltd purchased the design rights, weapons and spare parts of the Austrian NORICUM 155 mm GH N-45 towed artillery system.

No figures for Austrian production of the GH N-45 have been released but it is estimated that between 500 and 600 weapons were produced with production reaching 10 weapons per month.

Production by Voest-Alpine stopped in the late 1980s when it became apparent that the weapons were reaching the Middle East.

Known customers include Iran, Iraq and Thailand, but in some of these cases they were not supplied direct from Austria.

In mid-1997, the Royal Thai Army placed an order for a second batch of 36 155 mm GH N-45 howitzers in the latest A1 towed configuration and these were delivered in 1998.

The NORICUM 155 mm GH N-45 howitzer, firing an Extended Range Full Bore-Base Bleed (ERFB-BB) projectile, has a maximum range of 39.6 km so making it the longest range artillery system in service with the Royal Thai Army.

It is understood that small batches of GH N-45 systems could be made from existing stocks of spare parts. In the future new-build weapons will be supplied. As of early 2008 it is understood that no brand new GH N-45 155 mm gun-howitzers had been built.

The GH N-45 is, in most respects, similar in appearance to the Belgian GC 45 but has been redesigned in certain key areas to improve both handling in the field and reliability and to make the weapon easier to manufacture.

The carriage uses a walking beam suspension for improved cross-country mobility and a secondary float is fitted for easy emplacement, displacement and general weapon handling. There is a quick release in the traversing gear that brings the barrel from the travelling jack-knife position to the firing position in a few seconds and there is a steering device that allows the weapon to travel in the tracks of the towing vehicle. The GH N-45 can be airlifted by a Lockheed Martin C-130 transport aircraft without preparation and the normal towing vehicle is a 5 or 10 tonne 6 × 6 truck, with the travelling speed on all types of terrain limited only by the capabilities of the towing truck.

The GH N-45 can be delivered in a basic towed form or with an APU; an APU kit can be supplied for fitting to towed models by the user. The main power source is a Porsche 236 6.9 four-cylinder, four-cycle air-cooled 2.3 litre engine delivering 120 hp. The APU is mounted on the forward part of the carriage with the driver on the right. The APU enables the weapon to propel itself at a maximum speed of 30 km/h and two 30 litre fuel tanks provide sufficient fuel for ranges of up to 130 km. With the APU the weapon can climb 40 per cent gradients at a speed of 5 km/h.

The GH N-45 has a 45 calibre barrel with a 22.94 m3 chamber volume to enable base bleed ammunition to be fired to a maximum range of 39,600 m. The barrel has a semi-automatic breech mechanism with a pneumatic rammer. The overall length of the barrel, including muzzle brake and breech mechanism is 7,720 mm with the length of rifling being 5,830 mm and the length of chamber being 1,173 mm. The rifling has 48 grooves.

Extras available for the GH N-45 included a power elevating and traverse system, and an emergency ammunition bracket holding six standby 155 mm projectiles, both for the APU-powered version. A further option for the APU version was an ammunition-handling device. The jib and power unit for this device are mounted on the top right of the barrel and are used to raise the ammunition tray from ground level to the loading position. Tracks could be fitted to the APU-powered version to increase traction over soft ground and enable gradients of up to 45 per cent to be climbed. Also available for the APU version was a remote-control system that enabled a 6 × 6 tractor to use the traction of the powered carriage over adverse terrain giving a 10 × 10 configuration.

In addition to standard NATO ammunition, the 155 mm GH N-45 can fire a complete family of 155 mm ammunition, including:

• HE/BT, maximum range 30,300 m (charge N10)

• HE/BB, maximum range 39,600 m (charge N10)

• HC/smoke, maximum range 39,600 m (base bleed), 30,300 m (boat tail) (charge N10)

• WP/smoke, maximum range 39,600 m (base bleed), 30,300 m (boat tail) (charge N10)

• Illuminating, maximum range 39,600 m (charge N10)

• HE, 24,700 m (charge N10)

• HE (M107), 17,800 m (charge M119A2)

In addition to supplying the above types of 155 mm artillery projectile the company also claims to supply cargo munitions, terminally guided munitions and more advanced sensor fuzed munitions.

In addition, various types of artillery fuze can be supplied by NORICUM as well as various types of bagged and modular charge systems.