A highly versatile mobile suit created by the Earth Federation Forces (EFF) as part of the RX Project. The Gundam was developed to work in conjunction with RX-77-02 Guncannon, a medium-range artillery MS, and RX-75 Guntank, an artillery support MS. The Gundam featured a Core Block System which allowed the cockpit to separate and become the Core Fighter. Its armaments included head vulcans, beam sabers, as well as a beam rifle that even the Principality of Zeon had yet been able to put into practical use.
To counter Zeon's advantage with mass-produced mobile suits, the EFF launched Operation V on April 1, UC 0079 with an aim to create and mass-produce its own mobile suits. As part of Operation V's RX Project to be used as the EFF's trump card against Zeon, the Gundam and other RX-series MS underwent final testing at the EFF's secret base inside Side 7 colony since August. On September 18, Zeon's Major Char Aznable led a Zaku squadron comprised of Denim and Slender to infiltrate Side 7. Char and Denim's Zakus destroyed almost all of the base's RX-series mobile weapon parts including those of the Guncannons and Guntanks. While Denim's Zaku provided cover, Char stole the Gundam and defeated a lone Guncannon with its beam saber before he proceeded to hijack EFF's Pegasus-class carrier by killing its captain Paolo Cassius and destroying its main bridge. The EFF launched its mobile suits to attack Char's escaping fleet, and Char quickly sortied with the newly-acquired Gundam from the Pegasus carrier to counter the pursuing 01 Gundam and a EFF-captured Zaku. Char's Gundam fired the beam rifle for the first time and destroyed the EFF Zaku with a single shot, before it engaged the 01 Gundam in a fast and furious beam saber duel, with Char and his Gundam emerging victorious.