Entering service in 1963 the M109 155mm self propelled medium howitzer has proved to be one of the most successful and reliable artillery pieces of recent years. Development of the M109 began in 1952 as a replacement for the M44 and M107 Self Propelled howitzers (neither of which was air-portable) using the same hull chassis and turret of the M108 105mm SP light howitzer with a few modifications to accommodate the larger gun. The first prototype (powered by a petrol engine) appearing in 1959, with a second prototype being completed a year later with a diesel engine, and this has provided the standard powerplant of all subsequent machines. Production commenced in 1962.
The M109 is operated by a crew of six (commander, driver and four gun crew) and normally carries a load of 22 rounds of 155mm ammunition for the M185 (earlier models had the M126 cannon with 28 rounds) Howitzer.With the M185 a conventional High Explosive (HE) can be fired to a range of 19,794 yards (15,996 yard with the M126) or 26,246 yard using rocket propelled projectiles. The rate of fire is one round per minute (or three per minute over a short period). The gun tube can be elevated to 75 degrees and the turret traversed 360 degrees.
Built by the Allison division of General Motors Corp; Cadillac Motorcar Division of General Motors Corp; and the Chrysler Motorcar Corp (all in Detroit Michigan) the M109 is powered by a 405 bhp turbocharged V-8 Detroit diesel engine giving a speed of 35 mph over a range of 220 miles.
The M109 has been acquired by some thirty-five nations and has undergone many improvements over its long service. It has also spawned several variants based on the vehicle’s chassis including the XM975 Roland SAM system, and the M992 field artillery ammunition support vehicle (FAASV)