ADP 3-90, page 63

The Defense 31 July 2019 ADP 3-90 4-3 provide early warning and continuously disrupt enemy attacks. They employ protection efforts to preserve combat power. This includes protecting their forces from attrition by using available air and missile defense assets. They conduct information operations to prevent civilian interference with their operations. They perform military deception, cyberspace, and electronic warfare to inaccurately portray friendly forces’ locations, capabilities, and intentions to mislead enemy commanders and to deny those same enemy commanders the ability to use cyberspace and the electromagnetic spectrum. TYPES OF DEFENSIVE OPERATIONS 4-15. Friendly forces use three types of defensive operations to deny enemy forces advantages:  Area defense focuses on terrain.  Mobile defense focuses on the movement of enemy forces.  Retrograde focuses on the movement of friendly forces. AREA DEFENSE 4-16. The area defense is a type of defensive operation that concentrates on denying enemy forces access to designated terrain for a specific time rather than destroying the enemy outright. The focus of an area defense is on retaining terrain where the bulk of a defending force positions itself in mutually supporting, prepared positions. Units maintain their positions and control the terrain between the position of enemy forces and the terrain they desire. The decisive operation focuses fires into engagement areas, possibly supplemented by a counterattack. Commanders can use their reserve to reinforce fires, add depth, block, or restore a position by counterattack; to seize the initiative; and to destroy enemy forces. Units at all echelons can conduct an area defense. The Battle of Kursk in July 1943 is a historical example of an area defense by the Soviets. (See FM 3-90-1 for a discussion of the advantages and disadvantages of the use of a defense in depth and a forward defense during the conduct of an area defense.) MOBILE DEFENSE 4-17. The mobile defense is a type of defensive operation that concentrates on the destruction or defeat of the enemy through a decisive attack by a striking force. The mobile defense focuses on defeating or destroying enemy forces by allowing them to advance to a point where they are exposed to a decisive counterattack by a striking force. The striking force is a dedicated counterattack force in a mobile defense constituted with the bulk of available combat power. A fixing force is a force designated to supplement the striking force by preventing the enemy from moving from a specific area for a specific time. A fixing force supplements a striking force by holding attacking enemy forces in position, by canalizing attacking enemy forces into ambush areas, and by retaining areas from which to launch the striking force. German General Manstein’s Donbas Operation in the Ukraine in February 1943 was a mobile defense. 4-18. A mobile defense requires an AO with considerable depth. Commanders shape their battlefields causing enemy forces to overextend their LOCs, expose their flanks, and dissipate their combat power. Commanders move friendly forces around and behind enemy forces to cut off and destroy them. Divisions and larger echelon formations normally execute mobile defenses. BCTs and maneuver battalions participate in a mobile defense as part of a fixing force or a striking force. RETROGRADE 4-19. The retrograde is a type of defensive operation that involves organized movement away from the enemy. An enemy force may compel these operations, or a commander may perform them voluntarily. The higher echelon commander of a force executing a retrograde must approve the retrograde before its initiation. A retrograde is not conducted in isolation. It is always part of a larger scheme of maneuver designed to regain the initiative and defeat the enemy. 4-20. The three variations of the retrograde are delay, withdrawal, and retirement: