Military police

Military police, colloquially as MPs, are concerned with law enforcement on military property and concerning military personnel, installation security, close personal protection of senior military officers, management of prisoners of war, management of military prisons, traffic control, route signing and resupply route management. However, not all military police organizations are concerned with all of these. MPs are generally not frontline combat personnel, but their duties may bring them near the frontline.

In the Halo universe
The UNSC Marine Corps maintains its own military police, as does the UNSC Army, used to guard military installations on Reach and Earth, as well as other high priority installations.

It is unknown whether the UNSC Navy maintains its own MPs, though it is presumed that Marine MPs also function in coordination with the UNSC Navy. ODST MPs formed a security detail for the SPARTAN-117's testing of the Mark V MJOLNIR Armor.

Spartans also have a military police version of their armor.