Review & Build in Pictures of M109 from Zvezda in 1:100 scale

History & Derivatives:
The M109 was the medium variant of a U.S. program to adopt a common chassis for its self-propelled artillery units. The light version, the M108 Howitzer, was phased out during the Vietnam War, but many were rebuilt as M109s.
The M109 saw its combat debut in Vietnam. Israel used the M109 against Egypt in the 1973 Yom Kippur War and in the 1982 and 2006 Lebanon Wars. Iran used the M109 in the Iran-Iraq War in the 1980s. The M109 saw service with the British, Egyptian and Saudi Arabian Armies in the 1991 Gulf War. The M109 also saw service with the U.S. Army in the Gulf War, as well as in the Iraq War from 2003-2011.
Upgrades to the cannon, ammunition, fire control, survivability, and other electronics systems over the design's lifespan have expanded the system's capabilities, including tactical nuclear projectiles, Cannon Launched Guided Projectiles (CLGP or Copperhead), Rocket Assisted Projectile (RAP), FAmily of SCAtterable Mines (FASCAM), and improved conventional munitions (the Dual-Purpose Improved Conventional Munition, DPICM).
The Field Artillery Ammunition Supply Vehicle (FAASV) is built on the chassis of the M109-series. It is also colloquially referred to as a "CAT" (referring to its nomenclature, CAT: Carrier, Ammunition, Tracked). It replaces the M548 supply vehicle. Unlike the M548, it is armored. This ammunition vehicle has no turret, but has a taller superstructure to store 93 rounds and an equivalent number of powders and primers. There is a maximum of 90 conventional rounds, 45 each in two racks, and 3 M712 Copperhead rounds. Until recently, much of the remaining internal crew space was taken up by a hydraulically powered conveyor system designed to allow the quick uploading of rounds or transfer of rounds to the M109-series howitzer. Most early models had an additional mechanism called an X-Y Conveyor to lift the rounds into the honeycomb-like storage racks in the front of the superstructure. A ceiling plate above the two racks can be unbolted and opened to allow the racks to be winched out of the vehicle. This vehicle is fitted with a Halon fire suppression system and a weapons mount similar to that on the M109 turret, usually mounting a Mk 19 grenade launcher for local defense against infantry and light armored vehicles. The latest models have a mounting point for two secure radios.
The hydraulic conveyor system is removed by crews as it is slower than moving the rounds by hand. Recently the army has removed the conveyor system and changed the two horizontal opening doors to two vertical doors opening from the center to provide protection to the crew during transfers.
The vehicle also contains a 2-stroke diesel powered auxiliary power unit that can power all non-automotive energy requirements on the Field Artillery Ammunition Supply Vehicle and on the howitzer when a slave cable is used to connect the two. This reduces fuel consumption when mobility is not required.
Taken from Wikipedia.