What does a Military Police unit do?

Essentially, there are 4 basic Military Police missions in the battlefield. They are:

1) Maneuver, Mobility Support Operations (MMSO)
Effective use of the road network is a key component of all movement functions. Military units will be competing for road space. Combatants, stragglers, and refugees may further exacerbate roadway congestion. To ensure maximum use of the roadway network, MPs perform MMSO as needed. In doing so, MPs assist in the identification of primary and alternate routes, monitor route conditions and keep routes clear for vital military movements. Typically, these methods consist of the following procedures:

     ¤ Route Reconnaissance and Surveillance
     ¤ Regulation and Enforcement
     ¤ Damage assessment
     ¤ Information collecting, reporting and dissemination

2) Internment Operations
Internment refers to the wartime confinement imposed on prisoners of war (EPWs), and civilian internees (CIs). Commanders are responsible for the humane treatment of all EPWs and CIs. You've all seen this on television, but essentially, our MPs would receive EPWs' from the forward units (or wherever they are taken). They would search them and transport them to a safe area. Meanwhile, they would make arrangements with the Army to relinquish control to them. Historically and doctrinally, Marines don't maintain control of EPWs/CIs on the battlefield for very long periods of time. However, that doesn't preclude us from doing so.

3) Law and Order
Just like in garrison duty, there is still a need for a MP presence as there may be crimes that need to be investigated. For example, there may be a law of war violation that requires an investigation. There may be missing government property for which commanders may need assistance in locating or determining negligence/fault on a service member's behalf. Another example for this type of work involves the reports about the Soldier who threw the hand grenade into his fellow soldier's tent. This would be a mission MPs could face.

4) Area Security
This is much broader than walking circles around a command tent. Area security involves both foot and vehicular patrols, establishing/manning check points, conducting searches, and interviewing the local populace. Area security is a task that every unit in the Marine Corps does within their own command. However, MPs offer an ability to broaden the scope of Area Security by working outside of the immediate area for which they are assigned.