The Primus was developed and tested in secrecy over six years to fill a requirement for a tracked howitzer for use with armored battle groups, and is a pretty interesting example of what you can achieve by setting modest goals. For a start, the Primus is a light, 28 ton, 155mm, 39 caliber SPH (self-propelled howitzer), roughly half the weight of the German PzH 2000 (itself an improved version of the U.S. M-109). Weight was the principle design element of the Primus, as it was designed for use in the close, soft jungle terrain of South East Asia, and it could not exceed the 30 ton weight limit for crossing narrow road bridges.
The weight limitation means that the Primus seems limited when compared to other SPHs, like the AS90 Braveheart, and the PZH 2000. For example, its barrel is only 20 feet long, compared to 26 feet for most other SPH. Its its automated loader can carry only 22 ready rounds as opposed to the PzH2000's 55. Also, it only has a traverse of about 34 degrees.
In compensation, the Primus is a very agile for a tracked howitzer. It's 550Hp Detroit Diesel engine gives it a power to weight ratio of 19.43hp/ton, as opposed to the Braveheart's 15.7hp/ton. This means that it can accelerate from rest faster than the Braveheart, which helps gunners shoot and scoot away from counter artillery. With it's automatic Fire Control System and ring laser gyro and GPS navigation systems, the Primus can unlimber from march in less than a minute, fire an accurate 3 round burst in 20 seconds, and then scoot off within a minute. An automated fuse setter currently being developed will further shorten the firing time, which currently has a maximum of 6 rounds/minute.
The shorter barrel length may give the Primus a range disadvantage when compared to most other current SPHs, but a larger calibre howitzer would have increased the weight of the Primus above the maximum 30 ton limit. The Primus is also meant to operate just behind the Forward Edge of Battle, where response times and availability are more crucial than range.
Singapore has a long history of developing artillery. It's first howitzer,the FH88 155mm 39 caliber, was developed in 1988 with rumored input from South Africa, and was followed by the FH2000 52 caliber 155mm howitzer in the 1995. In 2002, during Asian Aerospace 2002, Singapore Technologies Kinetics unveiled a lightweight, 7 tons, 39 caliber 155mm howitzer mounted on a 4x4 chassis which can be carried under a Chinook. -- Shawn Chung
More on the Primus:
The Singapore Armed Forces (SAF) has put 18 new SSPH1 Primus Self Propelled Howitzers into service. The name Primus is derived from the Latin motto of the Singapore Army's Artillery Formation: In Oriente Primus, 'First in the East'.