Introduced in UC 0077, the MS-05B Zaku I was the Principality of Zeon’s first true mass production mobile suit. Although designed as a front line combat unit, the Zaku I was soon replaced by the improved MS-06F Zaku II as the mainstay of Zeon’s mobile suit forces. Early during the One Year War of UC 0079, most Zaku Is were relegated to menial construction and supply duties, although a few continued to serve in combat roles. During the war’s opening days, Zaku Is were also used in other combat-related work roles, such gassing of colony populations, attaching booster engines to space colonies to hurtle them towards Earth, and so on. It wasn’t until the last months of the war that Zeon, desperate after facing losses in Operation Odessa and Operation Star One, moved the old Zaku Is back to the front lines to reinforce their faltering main forces.