The Mars Zeon first appears in the manga series Mobile Suit Gundam F90, being a group of Principality of Zeon army remnants who fled to Mars, rather than to Axis, after the One Year War. The Mars Zeons were also nicknamed the Oldsmobile Army by the Federation, because of their use of mobile suits of old-style appearances.
Enduring on their own for a long time, the Mars Zeon was later reinforced by remnants of the second Neo Zeon movement. Using the former Neo Zeon members' AMS-119 Geara Doga mobile suits, The Mars Zeon were able to produce mobile suits, outwardly similar to the Principality's most famous designs, but possessing performance superior to the Geara Doga. Mars Zeon first made their presence known in U.C. 0120, when they stole one of the prototype F90 Gundam F90 units, leading the 13th Autonomous Corps to pursue them back to Mars. There, it was learned that the Mars Zeons had converted Olympus Mons into a gigantic rail cannon, and were planning on bombarding the Earth and destroying the Federation. Thanks to the efforts of the 13th Autonomous, however, the Mars Zeons were defeated and the Olympus Cannon was destroyed. The remaining Mars Zeon remnants left for the Earth Sphere.
In Mobile Suit Gundam F91: Formula Report 0122, The Oldsmobile Army eventually invaded Earth in U.C. 0122 under the leadership of Charles Rochester with the aid of the Crossbone Vanguard. The Oldsmobile Army's aim was to directly attack Earth using a mass driver base on the Moon. In truth, this attack was used as a diversion for the Crossbone Vanguard's invasion of the Frontier Sides. However, when the Federation started to deploy their down-scaled mobile suits, such as the F71 G-Cannon and the RGM-109 Heavygun, they proved to be very effective against Mars Zeon's larger mobile suits.