Primus is the first self-propelled heavy artillery gun of the Singapore Armed Forces. Image courtesy of Dave1185.
The Singapore Self-Propelled Howitzer 1 (SSPH 1) Primus on display at Marina South during National Day Parade, 2005 celebrations. Image courtesy of Huaiwei.
The Primus 155mm self-propelled howitzer is compatible with Nato type classified 155mm ammunition. Image courtesy of Sgt John G. Vannucci.
The Singapore Self-Propelled Howitzer 1 (SSPH 1) Primus being transported by Airbus A400M aircraft. Image courtesy of Pecon1.

Primus 155mm 39 Calibre Self Propelled Howitzer

The Primus 155mm 39 calibre self-propelled howitzer.

The Singapore Self Propelled Howitzer 1 (SSPH 1) Primus is a 155mm, 39 calibre tracked howitzer operated by the Singapore Armed Forces (SAF).

Developed jointly by the SAF, Defence Science and Technology Agency (DSTA) and Singapore Technologies Kinetics (ST Kinetics), Primus is the first self-propelled heavy artillery gun that entered service with the SAF.

Primus howitzer development

The plan to induct a new self propelled howitzer in the SAF was conceptualised in the early 1990s. Several existing systems have been considered but all of them failed to meet the requirements of the SAF.

“The highly mobile vehicle can operate on different terrains ranging from paved roads to soft soil.”

A decision was therefore made to build a completely new howitzer. The development of Primus began in May 1996 as a result of this decision. The major equipments were custom-built to suit the unique operational needs of the SAF. The first prototype was rolled out in April 2000.

Trials were continued for the two years that followed and more than 2,000 rounds were fired before the system was officially certified for field operations in September 2002. Primus completed its first live-firing during Exercise Thunder Warrior in February 2004.

Primus self propelled howitzer design

Primus uses the modified armoured hull of the proven United Defence (now BAE Systems) M109 155mm self propelled howitzer. The fully enclosed turret is mounted on the customised aluminium chassis.

The vehicle accommodates four crew members including a commander, driver, ammo loader and a charge loader. It was designed to carry high volumes of payload to targets within short time.

The high automation technology used in the Primus enables the minimal four-man crew to operate the system effectively. The howitzer shares several automotive components with the Bionix infantry fighting vehicle (IFV) operated by the SAF.

155mm 39 calibre gun

The 155mm 39 calibre gun is compatible with all Nato type classified ammunition. The gun can fire at a maximum rate of six rounds a minute. Its burst rate is three rounds in 20 seconds. The gun is capable of firing at a sustained rate of two rounds a minute for 30 minutes.

The fire range of the gun varies based on the projectile and charge combination used. Primus achieves a maximum range of 30km with an extended range projectile. The secondary weapon includes a 7.62mm general purpose machine gun.

Fire control

The main gun fire control is supported by the automatic fire control system (AFCS). The AFCS delivers enhanced target accuracy based on the target grid, available ammo and ballistic calculation. The accurate computation of firing data, input of ammunition data, correction for ammunition variance and environmental variation are performed by an on-board ballistic computer. The target information is conveyed with the battalion or forward observers through a datalink.

The automated projectile selection is made from a 22-round magazine using a patented ammunition handling system upon the activation of a fire mission.

The selected projectile is then immediately loaded and rammed. An automatic fuse setter (AFS) is being developed by ST Kinetics for an optimum burst effect. The AFS can operate on all types of Nato standard fuses.


The shoot and scoot capability of the howitzer enhances battlefield survivability. The vehicle takes less than 60 seconds from the firing configuration to move out of the counter-fire zone.

The self propelled Primus ensures better survivability of frontline troops by completing the action ahead of enemy counter-fire. It is fitted with two triple tube 76mm smoke grenade launchers for self-defence. The engine is protected with FESS fire suppression system.


Primus is powered by a Detroit Diesel 6V92TA diesel engine coupled to a HMPT-500-3EC fully automatic transmission. The engine develops a power of 550hp.


The highly mobile vehicle can operate on different terrains ranging from paved roads to soft soil.

“The plan to induct a new self propelled howitzer in the SAF was conceptualised in the early 1990s.”

It is equipped with an advanced positioning and navigation system for autonomous operations.

The system assists the howitzer to react quickly and also eliminates time consuming manual operations. Primus has a maximum speed of 50km/h and a cruising range of 350km.

Slope-climbing capability is 60%. The vehicle can ford a depth of 1.1m without preparation. It is airportable by Airbus A400M transport aircraft.

The Global Armoured Vehicles and Counter-IED Vehicles Market 2011-2021

This project forms part of our recent analysis and forecasts of the global armoured vehicles and counter-IED vehicles market available from our business information platform Strategic Defence Intelligence. For more information contact us: EMEA: +44 20 7936 6783; Americas: +1 415 439 4914; Asia Pacific: +61 2 9947 9709 or via email.