When there is an MP platoon in direct support of a maneuver brigade, that platoon supports the crossing without the need for additional MP support. Deliberate and retrograde river crossings, however, do require intensive MP support. Deliberate crossings require planned and augmented MP support. A buildup of firepower and equipment is needed on both the entry and the exit banks. Retrograde crossings also must be closely planned and controlled.
Timing is critical.
Massed crossing forces could slow momentum or exceed classification limits of the bridging. Forces moving to the rear may retrograde to defensive positions beyond the water obstacle. But they also may be slowed as they set up to defend the exit bank. You support retrograde crossings like you do deliberate crossings. You perform BCC within the crossing area and on the entry and exit sides of the river.