Following the events of The One Year War; Zeon sold off some of their older Zaku units as many were a war excedent following the adoption of new and better MS derived from tecnology obtained from the capture of the White Gundam.
The colonies consisting of the independent Side 6 would modify the Zakus they obtained into a special mobile suit police force in fear of a future Zeon (or any other) attack.
The police Zaku appears similar to the regular Zaku but with some minor alterations. The most notable of these alterations are its blue color scheme and shoulder-mounted police lights.
