In early 1994, it was revealed that the Finnish company VAMMAS, previously known as Tampella and more recently Patria Weapon Systems, had completed the prototype of a new 155 mm 52 calibre towed artillery system fitted with an Auxiliary Propulsion Unit (APU).

This weapon is known as the 155 GH 52 APU and was originally developed as a private venture together with the Finnish Defence Forces (FDF). It is a further development of the earlier 155 mm M-83 towed howitzer which was produced in two versions, neither of which has an APU, which are covered in a separate entry.

Development of the new 155 GH 52 APU commenced in 1990 with the first prototype being completed the following year. Firing trials were successfully completed in 1993.

It would be possible to upgrade earlier weapons to the new 155 mm 52 calibre version.

Following trials with prototype weapons under the designation of the KX, the Finnish Army placed an order for a quantity of weapons under the designation of the 155K98 with first deliveries taking place in 1998.

Late in 2000, another batch of 155 mm 155 GH 52 APU systems was ordered for the Finnish Defence Force, which brought the total number of systems up to 36 units.

This figure of 36 consisted of 27 + 9 with final deliveries under this contract made late in 2002. The first regiment was fully operational by 2001 and has a total of 18 guns in three batteries each of six guns, which can be further split into two troops each of three guns.

In the FDF the 155K98 is deployed as the Corps level artillery system with a total of three regiments formed with a total of 54 guns.

Current production models of the 155K98 for the FDF have been fitted with a TALIN (Tactical Advanced Land Inertial Navigation) system, a modern version of the Honeywell Modular Azimuth Position System (MAPS).

MAPS was originally developed for the US Army M109A6 Paladin with over 2,000 built for the home and export markets. The installation of TALIN on the 155K98 reduces the time taken to come into action time as well as increasing the accuracy of the weapon.

In August 1999, Patria Weapon Systems signed an agreement with the Arab Republic of Egypt under which Finland would transfer technology for the local production of the 155 mm 155 GH 52 which has the local designation of the 155 mm EH52 towed howitzer. The first complete Patria Weapon Systems 155 mm 155 GH 52 system was delivered to Finland in 2000. Prime contractor in Egypt is Factory 100 (Abu Zaabal Engineering Industries Company).

The 155 GH 52 APU weapon consists of five key components, barrel assembly, top carriage, bottom carriage, sighting devices and the APU.

The barrel assembly consists of the barrel, muzzle brake, fume extractor, breech piece, primer housing lock, firing safety lever, breech block safety lever and flick rammer safety lever.

The top carriage consists of the saddle, elevating mechanism, traversing mechanism gearbox, equilibrators, semi-automatic mechanism cocking device, layers pressure trigger, cradle, buffer, buffer replenisher, recuperator and the flick rammer.

The bottom carriage consists of the gun jack, firing platform, central structure, trail, trail support cylinder, walking beam, wheel, dolly wheel, trail connecting lock, trail support plate, towing eye, cabin, APU, mechanical control of hydraulic units, electric control of hydraulic units, external output for accessories and manual hydraulic pump.

Sighting devices covers indirect and direct firing. The sighting devices for indirect firing include elevation-setting mechanism, pitch levelling mechanism, cross-levelling mechanism, telescope mount holder and panoramic telescope illuminating equipment.

The panoramic telescope can also be used for direct firing but a special telescope, an elbow telescope sight, is normally used for direct firing. There is a mount for the elbow telescope on the gun layer's side of the gun.

The APU includes the control devices, steering panel, gauge panel, electric control of hydraulic units, mechanical control of hydraulic units, steering joystick, external output for accessories and manual hydraulic pump.

The 155 mm 52 calibre ordnance has a 23 litre chamber, semi-automatic horizontal sliding wedge breech mechanism, pneumatic rammer located on the left side to ram projectiles and charges at all angles of elevation and a single-baffle muzzle brake. A fume extractor is fitted as standard. The 23 litre chamber conforms to the NATO Joint Ballistic Memorandum Understanding (JBMoU).

The recoil brake is hydraulic while the recuperator is pneumatic. Recoil length depends on the charge and elevation but maximum recoil stroke is 1,500 mm.

The manual elevating and traverse mechanism is the same as that fitted to the earlier Patria Weapon Systems M-83 towed howitzer and is fitted on the left side of the carriage together with the direct and indirect sights. The split trail carriage is of a new design.

When deployed in the firing position, the forward part of the carriage rests on a hydraulically operated firing platform under the carriage, with each of the trails being provided with a spade, each of which is fitted with pegs to avoid the need to dig them in.

The weapon takes 2 minutes to come into action and is normally operated by a nine-man crew although two men can operate the system for a short period of time. When travelling, the 155 mm 52 calibre ordnance is traversed through a full 180° and locked in position over the closed trails. The travelling lock for the 155 mm ordnance is located on the right trail.

The carriage has four rubber-tyred road wheels, two either side, for high-speed towing with the suspension being of the walking beam type for improved cross-country mobility. In addition, there is a single dolly wheel on each trail leg to assist in bringing the weapon into action.

Mounted on the forward part of the carriage is the APU, a Deutz air-cooled turbocharged diesel developing 104.6 hp, coupled to a hydrostatic transmission which in turn powers the four motors located one at each wheel station.

The APU gives the system a maximum road speed of 15 km/h with two of the four wheels engaged or 7.5 km/h with all four wheels engaged. The driver is seated on the forward part of the carriage on the left side and steers the system using a small joystick. The fuel tank holds 5 litres of diesel fuel.

The installation of the APU enables the 155 GH 52 APU to be taken quickly out of action and deployed into positions that are not normally accessible by the prime mover.

A burst rate of fire of three rounds can be fired in 12 seconds with a normal rate of fire being 10 rds/min.

The FDF uses a local version of the French Nexter Systems (previously Giat Industries) 155 mm LU111 high-explosive projectile under the designation 155 tkr88 and this has a maximum range of 23.8 km without a base bleed (BB) unit.

The FDF has also adopted and taken into service the German Rheinmetall 155 mm DM 642 cargo projectile that has 63 bomblets each with a self-destruct mechanism.

Patria also market two of their own 155 mm projectiles, the 155 ERFB-N (Extended Range Full Bore - Nubbs) which has a maximum range with base bleed unit fitted of 42.5 km and the 155 mm ERFB-S (streamlined) which has a maximum range of 40.5 km with BB.

There is also a 155 mm 45 calibre version, without an APU, which is called the 155 GH 45. This remains at the prototype stage.