During the One Year War, the Earth Federation developed a system of interchangeable modules known as the G-Parts. These allowed rapid transformation of the unit to adapt to different combat conditions, even when it was out in the battlefield.
The G-Parts had an Easy Mode to allow them to operate without the Gundam torso, so they could continue playing a support role to the Gundam during battle. The G-Sky Easy was the standalone version of the G-Bull.
The Earth Federation designed the Core Block System modular units, known as the G-Parts, to support the RX-78-2 Gundam. There were two sets of G-Parts: the A-Parts and the B-Parts. A-Parts consisted of a nose with a canopy cockpit, a set of caterpillar treads, and a pair of beam cannons. The B-Parts was a fuselage with four thrusters.
The G-Sky was formed by combining the FF-X7 Core Fighter to the top of the Gundam’s torso, and the B-Parts to the bottom. The power generator from the Gundam provided the G-Sky with longer operation time compared to the Core Fighter.
The G-Sky was armed with vulcan guns and missile launchers for ranged attacks. These were mounted on the Core-Fighter modular unit of the support fighter.
25 mm vulcan guns
Two 25 mm vulcan guns were mounted in each side of the nose of the Core Fighter module. The four fire-linked guns were the primary weapon of the fighter. Although they were barely able to damage mobile suits, the gunfire could distract the mobile suit pilots while they try to take down the fighter.
The G-Sky had a missile launcher on each side of its nose. The missiles could be used against enemy mobile suits, ships or ground targets.
Behind the scenes
Kunio Okawara was the original mechanical designer.
The G-Sky only appeared in the Mobile Suit Gundam anime series. It was removed in the compilation movies, because Yoshiyuki Tomino wanted to make the movies closer to his vision of for the series. So elements that were considered closer to the super robot genre were replaced with real robot elements.
However, Yoshiyuki Tomino felt that the G-Sky was considered closer to the super robot genre, instead of the real robot genre that he envisioned for the series. Thus, the G-Sky was removed in the compilation movies, and was replaced by the FF-X7Bst Core Booster.