The TFA-4DE GaZuOOT is a minor refit of a previously existing mobile suit, the TFA-2 ZuOOT. The ZuOOT was originally fielded by ZAFT in the early stages of its invasion of Earth during the First Junius War, and used primarily as a rear-line artillery support unit for the much faster and more agile BuCUE. The GaZuOOT replaces the shoulder-mounted shell-firing cannons of its predecessor with a pair of heavy beam cannons, and has newly-designed arms that eschew conventional hands in favor of heavier armaments. All existing ZuOOTs were refitted into GaZuOOTs between 73 and 74, and it remains in service currently, although like the BuCUE there are plans to phase it out following the introduction of the YMF-3000 DOM Trooper.
While invading Earth during the First Junius War, ZAFT created the TFA-2 ZuOOT, an early-model mobile suit designed for ground combat at long range. The ZuOOT was unique in that it was one of, if not the first transformable mobile suit created, able to switch between a humanoid form and a more mobile tank form for greater speed as well as stability. Because its mobility was extremely poor in mobile suit mode, this configuration is rarely use. The ZuOOT's overall low mobility and heavy firepower saw it serve as a second-line artillery unit, primarily to provide support fire for BuCUEs or positioned on the outer decks of land battleships to serve as extra gun turrets.
Shortly after the war's end, the design was revised to create the TFA-4DE GaZuOOT. Essentially identical in almost every way to the ZuOOT, there were only small differences, primarily in its armament. First, the GaZuOOT lacked its predecessor's hands, which were eliminated in favor of a rapid-fire machinegun, and a twin missile launcher was added to each forearm. Second, its two dual-barreled shell-firing cannons were replaced with similarly sized beam weapons, greatly increasing its range and accuracy. The GaZuOOT's fire control and tracking systems were upgraded accordingly, and all ZuOOTs still in service were gradually refitted into GaZuOOTs.
The GaZuOOT would continue to see action throughout the war that breaks out following the Break the World Incident, notably in the first failed attack on the Alliance's Lohengrin Gate, where they were decimated by the Alliance's positron cannon after failing to destroy the mobile armor Gells-Ghe. GaZuOOTs would also participate in the attempts to stop the rampage of the GFAS-X1 Destroy. Their role in later engagements would be limited, but it would remain in service through and beyond the war's end. However, there are plans to retire the GaZuOOT, and late in the war a potential replacement is developed in the YMF-3000 DOM Trooper.