7-248. If there is no possibility of the encircled forces receiving relief from enemy forces outside the encirclement, commanders only organize an inner encircling arm. If there is danger of an enemy relief force reaching the encircled enemy force, commanders organize both inner and outer encircling arms. Commanders assign the outer encircling arm a security mission, an offensive mission to drive away any enemy relief force, or a defensive mission to prevent the enemy relief force from making contact with the encircled enemy force. Once the encirclement is complete, these inner or outer encircling arms form a perimeter.