Gundam is the titular mobile suit of Mobile Suit Gundam. The Gundam was incredibly advanced for its time. Built from lightweight Luna Titanium Alloy, its frame was both lighter than that of Zeon's mass-produced mobile suits and much sturdier, able to shrug off a Zaku II's machine gun fire with little to no damage. Its offensize power was above and beyond that of the Zeon Zakus.
The successor to the first fielded mobile suit, the Zaku II improved on everything the previous model offered. It was faster, far more durable, had a better Minovsky Reactor, and could be fitted with far more weapons. The Zaku II was the mainstay of the Zeon military for most of the One Year War.
The Gundam Barbatos is one of 72 "Gundam" frames that was produced and used in the Calamity War. After it was recovered, Chryse Guard Security used it as a power reactor; aside from the fact that its Ahab Reactors were still functional, this was done mainly because Barbatos' cockpit was missing when it was found. A new cockpit similar to the one used by the CGS mobile workers was installed prior to its redeployment by the 3rd Group. Poor maintenance over the centuries since the Calamity War has degraded the Barbatos' armor and full combat potential. This is later rectified by Teiwaz technicians, who not only restored the Barbatos to its original look but also returned it back to a performance close to its original.