By the outbreak of the One Year War the MS-05 Zaku was five years old and largely considered obsolete. The Mobile suit was developed as the first combat-use mass-production mobile suit, but it was soon superseded by the MS-06C Zaku II Early Production Type. After that it was phased out and mainly consigned to auxiliary duties such as training, construction and supply duties. It wasn't until the closing months of the One Year War that the Zaku I's finally saw front-line action and had a chance for some real glory. After Zeon's crushing defeat during Operation Odessa, Zaku I's reinforced their faltering main forces and saw some of the bitterest action of the entire war; fighting desperate rear guard and holding actions, often against the now superior Federation Mobile forces.