Early variants had a short, 23-caliber barrel. Later versions, including the M109A6 Paladin, have a 39-caliber barrel. The M109 has a crew of six: commander, gunner, driver and three ammunition ...

Consequently, the name M109 can refer to an older M109A2 howitzer taken from storage and the modern M109A6 Paladin system, which, along with its evolved version M109A7, forms the backbone of ...