Originally developed in AC 195 as a replacement for the aging OZ-06MS Leo, after the end of the conflict, the Barton Foundation quietly seized the Serpent production lines at the space colony X-18999 and began building its own mobile suit army. The Barton Foundation then began production of 500 Serpent units for its puppet military force, the Mariemaia Army. Intent on using the Mariemaia Army's force against the now de-militarized Earth Sphere United Nation, the Barton Foundation intended to follow through with its original plans to seize control of the Earth Sphere.

The MMS-01 Serpent, like its Leo predecessor, was a versatile mobile suit capable of being equipped for both space and land combat. Built of the new Neo-Titanium alloy, the Serpent was physically almost as strong as Gundanium and significantly cheaper to produce. Armed with shoulder missile launchers, the Serpent could also carry a variety of hand-carried weapons, such as a bazooka, a large beam cannon or a double-barreled Gatling gun similar to that carried by the XXXG-01H2 Gundam Heavyarms Kai. Since the Earth Sphere Unified Nation has scrapped all its own mobile suits, the Serpent carries no beam sabers or other anti-mobile suit weapons.

Source: Gundamproject.com, Gundam W: Endless Waltz DVD