During the stalemate period of the One Year War, the Earth Federation Forces were playing a fast game of catch-up on the introduction of mobile suits into warfare by the Principality of Zeon. One of their earlier prototypes is the groundpounding RX-79(G) Gundam Ground Type, based loosely on the original "Project V" prototype RX-78-2 Gundam operating elsewhere during the war. From the RX-79(G) comes another experimental unit, intended for mass-production. Called the RGM-79[G] GM Ground Type, it uses 80% of the same parts as its RX-79(G) predecessor, as well as its extremely durable Luna Titanium alloy armor, and its ability to use beam rifles, but is more powerful yet cheaper to produce.

Only 42 of these units are produced at the Federation's Jaburo military headquarters factory, and they are immediately put into combat for field testing. Twelve units are assigned to the Kojima Battalion stationed in Southeast Asia, with the rest participating in the Federation's "Operation Odessa" offensive in Eastern Europe. However, the GM Ground Type project is soon abandoned in favor of the later standard-model RGM-79 GM, which is even cheaper to build and can serve as a "multi-role" unit in both space and terrestrial environments.

Info from mecha domian.