The M109 is an American-made self-propelled 155 mm howitzer, first introduced in the early 1960s. It was upgraded a number of times to today's M109A6 Paladin. The M109 family is the most common Western indirect-fire support weapon of manoeuvre brigades of armoured and mechanized infantry divisions.

The M109 has a crew of six: the section chief, the driver, the gunner, the assistant gunner and two ammunition handlers. The gunner aims the cannon left or right (deflection), the assistant gunner aims the cannon up and down (quadrant). The M109A6 Paladin needs only a crew of four: the Commander, driver, gunner and ammunition loader.

The M109A2 variant incorporated 27 reliability, availability, and maintainability (RAM) mid-life improvements. Most notably, the long barrelled 155 mm M185 cannon in the M178 gun mount, ballistic protection for the panoramic telescope, counterbalanced travel lock, and the ability to mount the M140 alignment device. Stowage was increased from 28 rounds of 155 mm, to 36 rounds. .50cal ammunition remained at 500 rounds.

The M109 saw its combat debut in Vietnam. Israel used the M109 against Egypt in the 1973 Yom Kippur War and in the 1982 Lebanon War and 2006 Lebanon War. Iran used the M109 in the Iran–Iraq War during the 1980s.

The M109 saw service with the British Army, the Egyptian Army and Saudi Arabian Army 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

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British Army M109A2, Royal Artillery museum, London, in Operation Granby.
US Army M109A2, Battery B, 41st Field Artillery, 24th Infantry Division, Operation Desert Storm, Iraq 1991.
US Army M109A2, Battery B, 1-82 Field Artillery, 1st Cavalry Division, Operation Desert storm, Iraq 1991.
US Army M109A2, Battery A/C, 6-14 Field Artillery, 1st Armored Division, USA 1987.

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