The M109 was introduced in 1963, as a heavy self-propelled artillery unit designed to be deployed with its companion support vehicle the M992 Field Artillery Ammunition Supply Vehicle (FAASV). The original manufacturers were General Motors (Cadillac Motor Car Division), General Motors (Allison) and Chrysler Corporation from the years 1962-1969. In 1974, Bowen-McLaughlin-York (BMY) joined the list of manufacturers. A medium howitzer version, the M108 was introduced originally but was later canceled to minimize duplicity in the U.S. Fleet. The M109 has proved itself in combat in many theaters over the years and has been adopted as the mobile artillery platform of choice by over 40 nations.
The original versions were semi-mobile, where communications cable were required to be laid between the battery and command vehicles. Later versions utilize radio data communications, eliminating the hard-wired requirement and allowing the battery to be fully mobile. Improvements to the powertrain, armor, fire control and cannon have been incrementally developed and the vehicle is still in current production for the U.S. Army in the M109A7 configuration, which introduced many common components to the M2/M3 Bradley Fighting Vehicle, to improve supportability and mobility while automating many systems.
The M109’s power pack is located at the front right of the hull, with the driver section located at the front left. The turret is located over the rear section and can rotate 360°, with the main gun fitted into the forward panel. The commander’s cupola can hold a .50 or .30 machine gun if needed. It uses 7 double-tired road wheels to a hull side. The drive sprocket is located at front with track idler at the rear and no return rollers are used. For entry and exit of the vehicle, the crew can use the small door located at the rear, side panels, roof hatches and the cover over the driver compartment. The main guns have large muzzle brakes and are clamped to the hull when traveling. The crew was made of six members; driver, commander, 2 gunners and 2 loaders. The number of crew members has decreased throughout the years, as upgrades have come out.
The M109A6 version has been the standard for a few years and was named the Paladin after the inclusion of the Paladin Digital Fire-Control System (PDFCS). The A6 had numerous improvements, including secure radio, onboard diagnostics, and improved armor and powertrain. The current M109A7 is a major step forward for the M109 and includes a new chassis taken from the M2/M3 Bradley Fighting Vehicle, as well as a new power system, to drive the fully-digital electronics of the new A7.
There is an active industry both by the OEM, BAE Systems, and many independent Defence contractors, for the design and installation of
M109 Upgrades. In recent years, the U.S.A. and other Countries have contracted BAE and other Defence contractors, to provide support, repair, RESET, overhaul and upgrade of M109 fleets, both from older versions to newer versions, as well as to country-specific configurations. A variety of upgrades are available for most systems of the M109, some of which have been adopted by the U.S. Army, but many of which, although evaluated for adoption, are now used exclusively outside of the U.S.A. and BAE.