The M109 was introduced in the early 1960s to provide indirect fire support to armoured and mechanised infantry divisions. It has a crew of six. The M109 has seen a number of modifications. The M109G, also known as the M109A3G is armed with a 155mm M185 cannon in a M178 gun mount with stowage increased from 28 to 36 rounds. It can be identifed by the short barrel, double muzzle brake and large fume extractor.