They were developed as a successor to the RTX-65 Guntank Early Type, MBTs (Main Battle Tanks) which previously served as a main weapons of the Earth Federation Forces. They were created as a further development of the Guntank Early Type, which, in addition to tank-like bombardment capabilities, had humanoid torsos with arms equipped with manipulator-mounted quadruple auto-cannons that were capable of flexible attacks. While retaining the bombardment capabilities of the Guntank Early Type, the Guncannon First Type was developed as a bipedal walking weapon whose lower body could travel better on irregular terrain, enabling it to function like an infantry soldier and move more easily in response to the situation. Although it is a humanoid mobile weapon, it was developed with an overwhelming emphasis on artillery attacks, and thus the Earth Federation Forces categorized it as an MBT like its predecessor. Since the Guncannon First Type is intended for infantry-style operation, it has more versatile armament as well as better mobility compared to its predecessor. In addition to the long-range bombardment capabilities of the Guntank Early Type, it also emphasizes bombardment from medium range, and it is designed so that its equipment can be changed depending on the mission and the team organization .
60mm Vulcan Gun
Made for shooting live rounds, these were attached to both sides of the head. They were frequently used not only in ground attacks but also in close combat in battles against other mobile suits as a means of containment..
A mobile suit-sized bullpup assault rifle that fires solid rounds. A metal fitting is attached to the breech to clasp the upper arm.
Low Recoil Cannon
The Guncannon's main armament, it has less recoil than the large-caliber cannons of the Guntank Early Type.
An anti-ground weapon that fires solid rounds. The Gatling gun and the low recoil cannon can be attached to either shoulder.
An optional weapon that replaces the low recoil cannon. It fires unguided missiles.
Protective equipment for the mobile suit. A mount-latch for the upper arm and a grip for the manipulator is attached to its rear face.
As of U.C. 0078, the Earth Federation Forces were aware that Space Colony Side 3 (later the Principality of Zeon) were developing humanoid mobile weapons for use in a war of independence. The Federation Forces hope to resist them with a similar type of humanoid mobile weapon, the Guncannon First Type. Thus they have formed a mobile unit, the Iron Cavalry Squadron, made up of these new MBTs. Elite pilots have been undergoing training as part of this select team, with the highly regarded Lieutenant Junior Grade Erdush as their squadron commander. The Iron Cavalry Squadron functions as a squadron made up of four teams, each consisting of three machines .
During the battle of Mare Smythii, the Iron Calvalry Squadron was deployed to protect the defecting Dr. Minovsky from five pursuing Zeon mobile suits (four Zaku I and one MS-04 Bugu), making it the first actual battle between mobile suits. However, due to the Guncannon First Type's lack of mobility and overreliance on ranged weapons, the entire squadron was quickly wiped out by the Zeon mobile suits, which suffered no casualties.