China North Industries Corporation (NORINCO) is exporting a new 120 mm mortar version of the widely deployed 6x6 WMZ-551 amphibious armoured personnel carrier (APC) designated the SM4 120 mm self-propelled mortar (SPM).

The crew and diesel engine compartment is located at the front and for its new mission the roof line of the WMZ-551 has been raised towards the vehicle's rear to provide greater internal volume for the 120 mm muzzle-loaded mortar and its ammunition.

The driver is seated front left with the commander to the right and above the latter position is an unprotected pintle-mounted 12.7 mm machine gun (MG).

NORINCO is now marketing a number of remote weapon stations (RWSs) and one of these could potentially be fitted in place of the 12.7 mm MG to enable the weapon to be fired from under armour and environmental protection.

For use in high ambient temperatures an air-conditioning system is fitted as standard and the fully amphibious capability of the standard 6x6 WMZ-551 APC is retained.

With little preparation the WMZ-551 SM4 120 mm SPM is fully amphibious and propelled in the water by a shrouded propeller fitted one either side at the rear that enables the vehicle to reach maximum swimming speed of up to 8.5 km/h.

The system has a crew of five, including the commander and driver and NORINCO is quoting a gross vehicle weight of 17 tonnes including ammunition, and a maximum road speed of up to 100 km/h.

The 120 mm mortar is fitted with a specially designed recoil system to reduce the stress on the platform so that no stabilisers are required to be deployed before the weapon is fired.

The weapon is coupled to a computerised fire-control system (FCS) that enables the system to come into action, carry out a fire mission and then redeploy before the arrival of counter battery fire