The M109 is an American 155 mm turreted self-propelled howitzer, first introduced in the early 1960s to replace the M44. It has been upgraded a number of times, most recently to the M109A7.

The M109 has a crew of four: the section chief/commander, the driver, the gunner, and the ammunition handler/loader.The chief or gunner aims the cannon left or right (deflection) and up and down (quadrant).

The newest M109 version for US service is the M109A7, formerly known as the M109A6 Paladin Integrated Management (PIM). The M109A7 shares common chassis components with the Bradley Fighting Vehicle (BFV) such as the engine, transmission, and tracks. This creates commonality with other systems and maximizes cost-savings in production, parts inventory, and maintenance personnel.