In mid-2001, it was revealed that NORINCO (China North Industries Corporation) had developed a 120 mm self-propelled mortar system. It is based on a modified chassis of the WMZ-551 (6×6) series armoured personnel carrier (APC). This is in turn a further development of the WZ-551 (6×6) APC which has been in service with the People's Liberation Army (PLA) for many years.

China North Industries Corporation (NORINCO) presents the new 120mm wheeled self-propelled howitzer-mortar SM6 at Zhuhai air Show China 2016, based on the chassis of the WMZ551 6x6 armoured vehicle personnel carrier. The SM6 120mm self-propelled howitzer/mortar is the export version of the WMA029.

Mounted on the roof in the centre of the WMZ-551 hull is the fully enclosed turret. This is very similar to that used by the Russian 120 mm 2S23 NONA-SVK self-propelled mortar system mounted on a modified BTR-80 (8×8) APC chassis.

In 1997, it was reported that Russia was to supply China with 100 120 mm 2S23 NONA-SVK self-propelled mortar systems, whose existence was first revealed in 1990.

The United Nations Arms transfer lists for the period 1992 through to 2006 show no transfers of complete 2S23 systems from Russia to China. It does show the transfer of three 120 mm 2S9 systems from Ukraine in 2000.

Russian military sources however never confirmed this deal or the transfer of technology to China allowing local production of the 2S23 system, ever took place.

While the three-person turret resembles the Russian 2S23 NONA-SVK armed with a 120 mm 2A60 rifled ordnance, the actual ordnance used for the Chinese system is rather longer. It is similar to the Russian 120 mm 2A80 installed in the 2S31 Vena self-propelled gun/mortar system. This is based on a considerably modified BMP-3 chassis.

The fully enclosed power-operated turret is mounted on the roof of the vehicle at the rear and is armed with a 120 mm rifled barrel fitted with vertical sliding breech mechanism. Although its primary role would be indirect fire, it also has a secondary direct-fire role.

The 120 mm ordnance does not currently feature a fume extractor, thermal sleeve or muzzle brake. Turret traverse is through a full 360° with weapon elevation from -4 to +80°.

This fires three main types of 120 mm ammunition, mortar bomb, High Explosive (HE) and High-Explosive Anti-Tank (HEAT) projectiles with a total of 36 rounds being carried.

Details of the 120 mm ammunition types fired are given in Table 1. The 120 mm HEAT projectile is used in the direct-fire role and all of the projectiles have the propelling increments attached to the rear of the projectile.

The HE-RAP (high-explosive rocket-assisted projectile) is still under development. It has a muzzle velocity of 265 m/s, a maximum range of about 13,000 to 13,500 m and contains 3.2 kg of explosive.

Like the HEAT and HE-RAP, the 120 mm cargo projectile has a casing that is pre-engraved, which means that it has a tighter fit in the rifled ordnance. A total of 30 dual-purpose anti-armour/anti-personnel submunitions are carried, which are claimed to be able to penetrate 90 mm of conventional steel armour. This projectile has a muzzle velocity of 425 m/s and a maximum range of 9,300 m.

These two new natures of 120 mm ammunition offer a significant enhancement capability to the NORINCO 120 mm SPM. A total of 36 120 mm projectiles and their associated propelling charges are carried.

According to NORINCO, rate of fire depends on the type of ammunition used and the aiming and operating mode with maximum rates of fire being 6 to 8 rds/min for HE, 10 rds/min for mortar bomb and 4 to 6 rds/min for a HEAT round.

A semi-automatic loading system is fitted with direct and indirect fire sights provided. There are three aiming modes, automatic, semi-automatic and manual.

The complete system has a combat weight of 16.5 tonnes and a normal crew of four, consisting of the commander, gunner, loader and driver. It is powered by a Deutz BF8L413FC air-cooled diesel developing 320 hp, coupled to a ZF 6HP 500 fully automatic transmission with six forward and one reverse gears.

It is also fully amphibious, being propelled in the water by two propellers mounted one under either side of the hull at the rear. Before entering the water a trim vane is erected at the front of the hull and the bilge pumps activated.

Standard equipment includes powered steering on the front four road wheels, NBC system and a central tyre pressure-regulation system. A 12.7 mm machine gun is installed on the roof for local and air defence purposes and a bank of three electrically operated grenade launchers is mounted either side of the turret firing forwards.

This system has been designed to carry out direct and indirect fire engagements against a variety of targets including 'participating in landing and anti-landing operations'.