The RX-78-3 Gundam "G-3" first appeared as part of Mobile Suit Variations model kit series, designed by Kunio Okawara and later reappeared in the game Gundam Battle Universe and Gundam the Ride: A Baoa Qu.
During the attack on Side 7, in September UC 0079, two of the three RX-78 Gundam prototype mobile suits were destroyed. The destroyed parts made their way to the Pegasus-Class assault cruiser White Base, and then to the Earth Federation's General HQ in Jaburo. Once there, the parts were cobbled together and the RX-78-3 Gundam was born. The G-3 Gundam became a testbed for the magnetic coating that was later applied to Amuro Ray's RX-78-2 Gundam and his intended unit the RX-78NT-1 Gundam "Alex". Visually, the G-3 is very similar looking to the Gundam, except for its gray and light blue paint scheme. [Source: wikipedia]