Barrier troops

Barrier troops, blocking units, or anti-retreat forces are military units that are located in the rear or on the front line (behind the main forces) to maintain military discipline, prevent the flight of servicemen from the battlefield, capture spies, saboteurs and deserters, and return troops who flee from the battlefield or lag behind their units. Barrier troops differ from military police, as barrier troops exert their effect through physical presence near specific allied units, as a preventative measure against retreat and other actions, whereas military police apprehend and control those who have already done so, typically in a wider area.