The Primus 155mm Self propelled Gun is AKA as Singapore Self-Propelled Howitzer 1 (SSPH 1). The Singapore Armed Forces did consider purchasing other vehicles, but decided to go with a modified M109 hull due to the restrictions on local transportation.
The upgraded hull is delivered to Singapore Technologies Kinetics by United Defence (now part of BAE).
STK have designed and manufactured the turret which, they fit to the turret, which houses the locally manufactured 155mm bore / 39 length calibre main gun. It uses a semi automatic loader (standard – round is loaded auto, charge manually) and has a rate of 6 rounds per minute. It is rated to fire NATO 155mm allowing Singapore to save on operational costs by buying in rounds already in service in NATO. 22 rounds can be carried in the ready to use turret bustle mounted magazine. The vehicle is equipped with a digital Fire Control System and direct line sight.
The modified hull (driver front left with optional night vision) uses the same Detroit Diesel Corporation (DDC) 6V 92TA as used in the Singapore Bionix AFV, which generates 550hp. It gives a top road speed of 50km/h and operational range of 350km. The vehicle uses a 4 man crew 4 Commander, Driver, Ammo Loader and Charge Loader.
Despite entering service in 2002, the vehicle isn’t as capable as other modern SPG’s, but this is due to the vehicle being developed for fighting in its own back yard and as such is a perfect vehicle for the Singapore Armed Forces.