MCRP 12-10B.1, page 83

(1) Security Area. The defensive battle begins with a combined-arms force conducting security operations well forward of the main battle area. Security area missions can include screen , guard, and cover. Based on their assigned mission, security forces use all available combat power to gain time, destroy the enemy, or slow his/her momentum. The initial battle is fought using aviation assets and indirect fire weapons. (a) Value of Security Area Operations. Security area operations complement to the defense by: Alerting the defense to the strength, location, and general direction of the enemy’s main and supporting attacks Delaying enemy first-echelon detachments Initiating early engagement of enemy forces Deceiving the enemy as to the true location of the defender’s main forces and main effort. Figure 3-5. Organization of the Battlefield (b) Withdrawal of Security Area Forces. The urban environment may complicate battle handover from the security force to the main battle area force. However, this transition must be accomplished smoothly to prevent the enemy from gaining momentum. The withdrawal of the security area forces must not result in an easing of pressure on the enemy. MCWP 3-35 .3 3-12