The Model 839P is a version of the Soltam M839 howitzer, fitted with an Auxiliary Power Unit (APU) for self-propulsion and various gun services such as opening and closing the trail legs. It was first demonstrated in 1983. It was followed in 1984 by the Model 845P, which was similar but was fitted with a 45 calibre barrel in place of the 39 calibre barrel of the Model 839P. In many ways the Model 845P is similar to the Model 839P. The M845P is also available without the APU in which case total weight is 9,400 kg.

In 1995, Soltam stated that guns with a 155 mm 52 calibre NATO standard barrel could be supplied by special request. As far as is known the 155 mm/52 calibre model has yet to enter production. This has been developed for the export market.

This Soltam 155 mm system, when fitted with a 45 or 52 calibre ordnance and an APU has also been referred to as the TIG 2000.

The complete weapon consists of two major assemblies, the ordnance and the carriage, plus the APU. The driver's position is on the left of the barrel and his controls include a starter, a speed range selector, a single control joystick and a parking brake. The driver's control position is attached to the central saddle structure along with the driver's seat and a safety belt. For firing, the control position is folded downwards. The howitzer can be controlled either from the seat or from the ground with the driver walking alongside.

The ordnance for the Model 839P is 39 calibres long (Model 845P 45 calibres) and is a monobloc autofrettaged component with a horizontal sliding breech block. Obturation is by self-sealing obturator discs. Standard-type primer cartridges are used and are ejected automatically from the breech block on run-out. A single-baffle muzzle brake is fitted along with a fume extractor located just over halfway along the barrel. Progressive twist rifling is employed. The hydraulic recoil buffer incorporates a variable length mechanism as well as a run-out control plunger, and the recuperator is hydropneumatic. Elevating and traverse gears incorporate `no back' mechanisms and pneumatic equilibrators balance the elevated mass. A quick-release device is incorporated into the elevating mechanism for loading. A pneumatic rammer is mounted on the elevating mass and can operate at all angles of elevation.

The carriage comprises two main parts, the superstructure (the upper carriage) and the basic structure (the lower carriage).

The superstructure includes the saddle and cradle which enable the gun to be laid in both elevation and azimuth. The basic structure, which is the main support when the weapon is in both firing and transport configurations, consists of its central structure with the main bearing, trails and the suspension.

The cradle carries all of those parts of the gun that recoil as well as those that move vertically during elevation and depression. The central part of the cradle carries the barrel assembly. On the top are the recuperator cylinders, at the bottom the buffer cylinder and the elevation arc. At its rear end are the trunnions, left and right, and at its front end the pivot pins for the equilibrators. The recoil length cut-off gear is located at the lower right front end of the cradle.

The saddle is of all-welded construction and screwed to the bearing's rotating part at the bottom and carrying the cradle at its top. The equilibrators act as a self-adjusting force for the barrel allowing easy laying and adjusting in elevation and depression.

The traversing mechanism is mounted on the front part of the saddle and serves to lay the gun in azimuth. For fast deflection or when rotating the barrel from the firing into the travelling position (or vice versa) the mechanism can be disengaged allowing free lateral movement of the barrel.

When deployed in the firing position, the system rests on three points, the firing platform and the trail spades. Lifting the howitzer off the ground, so that it is supported on the firing platform, is carried out by an electric hydraulic pump, battery operated with a mechanical back-up.

The suspension consists of four wheels; two pairs mounted together on a walking beam. This allows the weapon to be towed at any reasonable towing speed. Each individual wheel has a pneumatic brake cylinder operated by compressed air that is provided from the towing vehicle.

The weapon can be used for direct and indirect fire missions and is fitted with two different sighting systems, both of which are mounted on the left side of the weapon.

If required an advanced gun laying system can be fitted, based on a ring laser gyro. As an option, north finder, Global Position System (GPS) and navigation modules can be fitted.

The carriage is fitted with an ammunition handling crane mounted on the right trail leg. On the left trail leg is an APU which is a Deutz F4L/912 air-cooled diesel unit providing 80 hp at 2,600 rpm. The engine powers a hydraulic unit which in turn powers the driving wheels via hydraulic motors on the wheels. The system also powers a hydraulic ram on the left trail leg, which assists in spreading and closing the trail legs and lifting the howitzer off its wheels as well as assisting the howitzer off its towing vehicle. The firing platform is also hydraulically operated. For silent or emergency operation, the hydraulic system includes an electric motor powered by two in-line connected 12 V batteries and a hand pump is also supplied.

The Model 839P is able to drive under its own power at speeds of up to 17 km/h on roads. The maximum operating range is 70 km. Only one joystick control lever is required for direction or turning and when released it acts as a brake.

The Model 845P only differs from the Model 839P in barrel length and slight changes in overall weight.

The Model 839P and Model 845P can be supplied without an APU. Guns without the APU are known as the Model 839 or Model 845. Ballistic performances remain the same as guns fitted with an APU.

The TIG 2000 can be fitted with a 45 calibre ordnance with a chamber volume of 25.7 litres (empty) or 52 calibre ordnance with a chamber volume of 25.15 litres (empty). Both types are rifled 1:20 right handed twist, 48 grooves, as required by the Joint Ballistic Agreement. Switching from 45 to 52 calibre configuration also requires the replacement of the tube and assembly and an elongated towing rod.