This 170 mm self-propelled gun was first observed by US sources in the city of Koksan in 1978 and is therefore referred to as the M1978 self-propelled gun Koksan.

A number of these guns were supplied to Iran by North Korea and some were subsequently captured by Iraq in 1987-88.

In North Korean service, it is believed that the 170 mm Koksan is employed in regiments with a total of 36 weapons.

The system is based on a modified China North Industries Corporation (NORINCO) Type 59 MBT chassis with the existing welded steel turret armed with a 100 mm gun removed and plated over. A 170 mm gun of a previously unknown type in an open mount has been mounted on top of the chassis at the very rear. The driver of the Koksan is seated at the front of the hull on the left side, under full armour protection. As far as it is known, the chassis of the Koksan provides the same level of protection as the Type 59 MBT.

At the very rear of the chassis are two large spades that are lowered to the ground manually before firing commences; when travelling these are vertical. A large ordnance travelling lock is pivot-mounted on the glacis plate and this folds forward onto the ground when deployed in the firing position.

The long 170 mm ordnance is fitted with a multislotted muzzle brake but has no fume extractor. The screw-type breech mechanism opens to the right with a loading tray mounted on the left side of the weapon. In addition, there is probably a power rammer.

Elevation and traverse appear to be powered, although traverse is very limited to avoid overstressing the chassis.

It is possible that the 170 mm weapon used may be a Russian naval or coastal weapon supplied to North Korea in the 1950s for use in the coastal defence role. When these were replaced by surface-to-surface missiles, the coastal guns were surplus to requirements and could then have become available for mounting on the tracked chassis.

As there is insufficient space for the gun crew and ammunition on the Koksan, another vehicle is required to support the system in action and this would carry the remainder of the crew and some ready use ammunition. It is thought that the ammunition resupply vehicle is based on a full-tracked chassis.

It is probable that standard equipment for the 170 mm M1978 includes an NBC system and infra-red night vision equipment for the driver.

Like the Type 59 MBT on which it is based, the 170 mm M1978 self-propelled gun can lay its smoke screen by injecting diesel fuel into the exhaust outlet on the left side of the hull.

• 170 mm M1989 SPG

This is understood to use the same weapon and mount as the M1978 but is mounted on a modified AT-S full tracked carrier chassis. The current status of the M1989 is uncertain.

Production complete. In service with Iran and North Korea. Recent information has indicated that these systems may no longer be deployed in a fully operational role. They have not been seen in any of the recent North Korean military parades.