From Halopedia, the Halo wiki
The Arcadian Patrol was a primary law enforcement agency on the human colony world of Arcadia. During the Human-Covenant War in 2531, the unit saw action in the Battle of Arcadia and took part in civilian evacuation efforts.
When the Covenant attacked Pirth City, the Arcadian Patrol fought the aliens alongside the SPARTAN-II Red Team. The policemen were obviously no match for the invaders, but kept fighting in order to give civilians time to evacuate.
Particularly heavy fighting took place around the subways, where Covenant ambushed desperate civilians leaving the subways, while squads of policemen engaged the Covenant to little success. Fortunately for the policemen, reinforcements from the Phoenix-class colony ship UNSC Spirit of Fire soon arrived to relieve them, and the subways were quickly secured. The majority of the Arcadian Patrol moved on to defend the three evacuation ships, but some squads of police were evacuated alongside civilians.
Alongside the Spartans and Marine forces, the Arcadian Patrol suffered heavy casualties but was able to hold off the Covenant long enough for hundreds of civilians to escape.
It can be assumed that it was dissolved after the battle, because the remainder of the colony (mostly located in Abaskun) fell into lawlessness.
Unlike other contemporary police forces such as the New Mombasa Police Department, the Arcadian Patrol was incredibly lightly equipped. Officers were only equipped with basic uniforms and little/ no armour, and no weaponry or vehicles aside from basic pistols and police cars.
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