Soldiers tactical movement across terrain

Mobile Defense

A mobile defense focuses on destroying the attacking force by permitting the enemy to advance into a position that exposes the enemy to counterattack and envelopment. The commander retains the majority of available combat power in a striking force for the decisive operation, a major counterattack. The commander commits the minimum possible combat power to the fixing force that conducts shaping operations to control the depth and breadth of the enemy’s advance. The fixing force also retains the terrain required to conduct the striking force’s decisive counterattack. The area defense, on the other hand, focuses on retaining terrain by absorbing the enemy into an interlocked series of positions, where the enemy is destroyed largely by fires.

NOTE: The Army and Marine Corps concept and terminology for the conduct of a mobile defense are different. The Marine Corps does not use the fixing and striking force terminology. The Marine Corps discussion of a mobile defense addresses allocating minimum forces to a positional defense while allocating maximum combat power to counterattack forces.


8-1. The mission variables of mission, enemy, terrain and weather, troops and support available, time available, and civil considerations (METT-TC) may dictate that a unit conducts a mobile defense when defending against an enemy force with greater combat power but less mobility. The following circumstances favor the conduct of a mobile defense—

  • The defender possesses equal or greater mobility than the enemy.
  • The frontage assigned exceeds the defender’s capability to establish an effective area or positional defense.
  • The depth of the area of operations (AO) allows the attacking enemy force to be drawn into an unfavorable position where it can be attacked.
  • Time for preparing defensive positions is limited.
  • Sufficient armored, Styker, aviation, and long-range artillery forces and joint fires are available to allow rapid concentration of combat power.
  • The enemy may employ weapons of mass destruction because this type of defense reduces the vulnerability of the force to attack and preserves its freedom of action.
  • The mission does not require denying the enemy specific terrain.
  • The AO lacks well-defined avenues of approach and consists largely of flat, open terrain.

8-2. Commanders conducting a mobile defense anticipate enemy penetration into defended areas and use obstacles and defensive positions to shape and control such penetrations. They also use local counterattacks to either draw the enemy into entering planned penetration areas or to deceive the enemy commander as to the nature of the defense. Among other risks associated with the conduct of a mobile defense are—

  • The fixing force may be isolated and defeated in detail because of the need to resource the striking force to the detriment of the fixing force.
  • Operations in noncontiguous AOs associated with conducting a mobile defense can lead to defeat in detail.
  • Enemy operations may impair the ability of the striking force to react at critical points.
  • The enemy may not move into the area intended by the defending commander.
  • The attacking enemy force retains at least some momentum as it approaches the desired engagement areas (EAs).
  • The defending force may not gain an accurate picture of the enemy’s locations and dispositions required by the striking force to launch decisive operations in time to react.
  • The decentralized operations required by the mobile defense increase the potential for friendly fire incidents.

8-3. Future technology associated with mission command systems should improve the ability of the friendly force to gain and maintain a common operational picture, which reduces the risk associated with this type of defense. Figure 8-1 depicts Army units conducting a mobile defense.


8-4. Units smaller than a division do not normally conduct a mobile defense because of their limited capabilities to fight multiple engagements throughout the width, depth, and height of the AO while simultaneously resourcing striking, fixing, and reserve forces. Typically, the striking force in a mobile defense may consist of one-half to two-thirds of the defender’s combat power. Army brigade combat teams (BCTs) and smaller units generally conduct an area defense or a delay as part of the fixing force as the commander shapes the enemy’s penetration, or they attack as part of the striking force. Alternatively, they can constitute a portion of the reserve.


8-5. Army commanders organize the main body into two principal groups—the fixing force and the striking force. In the mobile defense, reconnaissance and security, reserve, and sustaining forces accomplish the same tasks as in an area defense. The commander completes any required adjustments in task organization before committing subordinate units to combat. (See figure 8-2.)

8-6. Organized by the commander with the minimum combat power needed to accomplish its mission, the fixing force turns, blocks, and delays the attacking enemy force. It tries to shape the enemy penetration or contain the enemy’s advance.

Typically, it has most of the countermobility assets of the defending unit. The fixing force may conduct defensive actions over considerable depth

Figure 8-2. Army organization of forces for a mobile defense within the main battle area (MBA). However, it must be prepared to stop and hold terrain on short notice to assist the striking force on its commitment. The operations of the fixing force establish the conditions for a decisive attack by the striking force at a favorable tactical location. The fixing force executes its portion of the battle essentially as a combination of an area defense and a delaying action. The actions of the fixing force are shaping operations.


8-7. The striking force decisively engages the enemy as attacking enemy forces become exposed in their attempts to overcome the fixing force. The term “striking force” is used rather than reserve because the term “reserve” indicates an uncommitted force. The striking force is a committed force and has the resources to conduct a decisive counterattack as part of the mobile defense. It is the commander’s decisive operation.

8-8. The striking force contains the maximum combat power available to the commander at the time of its counterattack. The striking force is a combined arms force that has greater combat power and mobility than the force it seeks to defeat or destroy. The commander considers the effects of surprise when determining the relative combat power of the striking force and its targeted enemy unit. The striking force is normally fully task organized with all functional and multifunctional support and sustainment assets before its actual commitment. The commander positions engineer mobility-enhancing assets with the lead elements of the striking force.

8-9. The striking force is the key to a successful mobile defense. All of its contingencies relate to its attack. If the opportunity does not exist to decisively commit the striking force, the defender repositions forces to establish the conditions for success. The striking force must have mobility equal to or greater than that of its targeted enemy unit. It can obtain this mobility through proper task organization, countermobility operations to slow and disrupt enemy movements, and mobility operations to facilitate the rapid shifting of friendly formations. The striking force requires access to multiple routes because an attacking enemy normally goes to great length to deny the defending force freedom of action.

8-10. The commander responsible for orchestrating the overall mobile defense should retain control of the striking force unless communication difficulties make this impossible. Normally this is the overall defending force commander. The commander’s most critical decisions are when, where, and under what conditions the commander should commit the striking force. The commander normally accompanies the striking force.

8-11. Resourcing a reserve in a mobile defense is difficult and requires the commander to assume risk. The commander generally uses the reserve to support the fixing force. However, if the reserve is available to the striking force, it exploits the success of the striking force.


8-12. A commander conducting a mobile defense uses control measures to synchronize the operation. These control measures include designating the AOs of the fixing and striking forces with their associated boundaries, battle positions, and phase lines. The commander designates a line of departure or a line of contact as part of the graphic control measures for the striking force. The commander may designate an axis of advance for the striking force. The commander can designate attack by fire or support by fire positions. The commander uses EAs, target reference points, targeted areas of interest, and final protective fires as necessary. The commander designates named areas of interest (NAI) to focus the efforts of reconnaissance and surveillance assets. This allows the commander to determine the enemy’s chosen course of action (COA). The commander designates checkpoints, contact points, passage points, passage routes, and passage lanes for use by reconnaissance and surveillance assets, security units, and the striking force. (See figure 8-3 on page 8-4.)

8-13. The commander must provide the striking force commander with control measures to focus the striking force at the decisive time and place and to deconflict fires with the fixing force. As a minimum, the striking force commander needs to know the anticipated objective decision points that could lead to the commitment of the striking force, limit of advance, and boundaries of the striking force’s AO. If the overall commander imposes either an axis of attack or a direction of attack as a control measure, that higher commander restricts the striking force commander’s freedom of maneuver. However, such restrictions may be necessary to avoid contact with enemy forces that could distract the striking force from accomplishing its primary mission. The commander may have to determine and transmit these control measures rapidly while the commander, staff, and subordinates move to take advantage of an opportunity to commit the striking force in a decisive counterattack. They should also help the commander recover the defense’s integrity, if the striking force is not successful in its attack. (Appendix A explains these control measures.)


Figure 8-3. Mobile defense control measures


8-14. The key to a successful mobile defense is the integration and synchronization of all available assets to maximize the combat power of the defending unit, particularly the striking force. The commander achieves integration and synchronization when employing their combined effects at decisive times and places. (The general defensive planning considerations addressed in chapter 6 apply to the mobile defense.)

8-15. Just as in an area defense, in a mobile defense the unit’s plans must address how the preparations for, and the conduct of, the mobile defense impact the civilian population of the AO. This is even more important during a mobile defense than it is during an area defense because the scope of maneuver and tempo of operations tends to be much larger. Civilian attempts to avoid advancing enemy formations and locations where combat occurs will impede the ground maneuver of defending units unless steps are taken to account for their presence and provide alternative routes for these dislocated civilians to use. Commanders communicate these routes to the civilian population by a wide variety of means to ensure they receive the information. Ideally, host nation civilian or military organizations will provide civilian traffic regulation and immediate essential services along those civilian evacuation routes (along with the other four primary stability tasks). However, if the host nation cannot perform these tasks, the defending unit will have to perform them. Screening of civilians by units is necessary in this case to preclude enemy agents from using these routes to infiltrate friendly defensive positions. At all times, commanders must meet legal obligations to local civilian populations.



8-16. The commander’s ability to maintain the mobility advantage of the force is an important aspect of the mobile defense. This mobility advantage may result from or be enhanced by countermobility actions directed against the attacking enemy force. In the mobile defense plan, the commander ensures that subordinate forces—including reserves and the striking force—can move freely around the battlefield, while at the same time restricting the enemy’s mobility, slowing the enemy’s momentum, and guiding or forcing the enemy into areas that favor the defense.

8-17. Most of the commander’s countermobility assets support the operations of the fixing force. Most of the commander’s mobility assets support the operations of the striking force. Situational obstacles provide a tremendous advantage to the defender in the conduct of a mobile defense. These obstacles are a combat multiplier because they enable economy of force measures. The commander uses situational obstacles to exploit enemy vulnerabilities, exploit success, separate enemy follow-on forces, and provide flank protection.


8-18. The effectiveness of a mobile defense is based on the carefully planned fires of all weapons. The striking force conducts the commander’s decisive operation in a mobile defense. It requires continuous and concentrated fire support. The commander weights the decisive operation, in part, by allocating field artillery and other fire support weapon systems to it. The commander rapidly shifts indirect fire support from the fixing force to the striking force. These fire support systems do not have to move with the striking force, if it remains within supporting range.

8-19. If the striking force’s planned maneuver places it outside the supporting range of the defending commander’s fire support systems, the commander must either plan to move fire support assets to locations where they can support the striking force or incorporate them into the striking force. Fire support assets, especially when employing precision munitions, can partially compensate for a lack of maneuver forces in the striking force. The commander takes precautions to prevent fratricide as the striking force approaches the fixing force’s EAs by establishing restrictive fire lines (RFLs), while supporting air and artillery assets interdict enemy movements.


8-20. When planning for the mobile defense’s sustaining operations, sustainment planners must look beyond the fixing force’s shaping operations to support the striking force’s decisive counterattack. The greater the distance the striking force must cover when moving from its assembly area (AA) to its final objective, the greater the amount of supplies needed to support that move. Once committed, units in the striking force require priority of fuel, ammunition, and maintenance support over comparable units in the fixing force. Commanders establish casualty treatment and evacuation procedures for both the fixing force and the striking force. The fixing force will likely suffer a higher percentage of casualties than the striking force as it absorbs the enemy’s attack. When the striking force must move a considerable distance from its sustaining base, the commander should consider establishing an intermediate staging base (ISB). Before establishing an ISB, the commander must weigh the benefits of establishing the base against the cost in terms of combat power or effort diverted from the support mission to secure the ISB. (See FM 3-35 for additional information on ISBs.)


8-21. Preparations for conducting a mobile defense include developing the fixing force’s defensive positions and EAs. The commander aggressively uses reconnaissance assets to track enemy units as they approach. Engineers participate in conducting route and area reconnaissance to find and classify existing routes. They improve existing routes and open new routes for use during the battle.

8-22. The striking force assembles in one or more areas depending on the width of the AO, the terrain, enemy capabilities, and the commander’s intent. Before the enemy attack begins, the striking force may deploy some or all of its elements forward in the MBA to—

  • Deceive the enemy regarding the purpose of the force.
  • Occupy dummy battle positions.
  • Create a false impression of unit boundaries, which is important when operating with a mix of armored, Stryker, and infantry forces or multinational forces.
  • Conduct reconnaissance of routes between the striking force’s AAs and potential EAs.

8-23. The enemy attempts to discover the strength, composition, and location of the units that constitute the fixing force and the striking force. The commander uses protective measures, such as security forces and operations security, to deny the enemy this information and degrade the collection capabilities of enemy reconnaissance and surveillance assets. The commander routinely repositions to mislead the enemy and to protect the force. In addition, the commander incorporates information protection and other defensive measures into plans and preparations. The commander attempts to portray an area defense to the enemy while hiding the striking force.


8-24. This publication divides the execution of a mobile defense into five steps for discussion purposes. The length and nature of each step, if it occurs at all, varies from situation to situation according to the mission variables of METT-TC. These steps are gain and maintain enemy contact, disrupt the enemy, fix the enemy, maneuver, and follow through. The first three are normally shaping operations within a mobile defense. The maneuver step is normally the mobile defense’s decisive operation, while the follow through step is normally a branch or sequel operation.

8-25. A commander executing a mobile defense must have the flexibility to yield terrain and shape the enemy penetration. The commander may even entice the enemy by appearing to uncover an objective of strategic or operational value to the enemy. The striking force maneuvers to conduct the decisive operation—the counterattack—once the results of the actions of the fixing force shape the situation to meet the commander’s intent.


8-26. The commander conducting a mobile defense focuses on discovering the enemy’s strength and exact locations to facilitate the effectiveness of the striking force. The security force (guard or cover) or the fixing force confirms the enemy’s COA and the main avenues of approach used by the enemy. The commander normally tasks other reconnaissance and surveillance assets to determine the location of enemy reserves and follow-on forces. Early detection of the enemy’s decisive operation provides the commander with reaction time to adjust the fixing force’s positions and shape the enemy penetration, which, in turn, provides the time necessary to commit the striking force. The striking force commander requires as close to real-time updates of the enemy situation as possible to ensure that the striking force engages the enemy at the right location and time.

8-27. While conducting delaying operations (see FM 3-90-2), the security force determines what routes the enemy is using, where the enemy is strong or weak, and where gaps in and between enemy formations exist. This information aids the commander in seizing the initiative by identifying opportunities. Further, it helps direct the striking force along the path of least resistance, as it maneuvers to employ its combat power at the critical time and place.


8-28. In a mobile defense, the commander conducts shaping operations designed to shape the enemy’s penetration into the MBA and disrupt the enemy’s introduction of fresh forces—reserves and follow-on echelons—into the fight. These shaping operations help establish the preconditions for committing the striking force by isolating the object of the striking force and destroying the enemy’s key command and control (C2) nodes, logistics resupply units, and reserves. Whenever possible, the commander sequences these shaping operations, to include electronic warfare, so that their effects coincide with the commitment of the striking force. To generate a tempo that temporarily paralyzes enemy C2, the commander may increase the intensity of these shaping operations dramatically on the commitment of the striking force. The commander continues to conduct shaping operations once the striking force commits to prevent enemy forces from outside the objective area from interfering with the decisive counterattack.


8-29. Fixing the enemy is the second half of shaping operations and establishes the conditions necessary for decisive operations by the striking force. Typically, the commander of the defending force allows the enemy force to penetrate the MBA before the striking force attacks. (See figure 8-4.) The fixing force may employ a combination of area defense, delay, and strong point techniques to shape the enemy penetration. The intent of the fixing force is not necessarily to defeat the enemy but to shape the penetration to facilitate a decisive counterattack by the striking force. The commander ensures that the missions and task organization of subordinate units within the fixing force are consistent with the concept for shaping the enemy penetration. Defensive positions within the fixing force may not be contiguous since the fixing force contains only the minimum-essential combat power to accomplish its mission.


Figure 8-4. Mobile defense before commitment of striking force

8-30. The fixing force’s extensive use of obstacles supports this shaping effort and helps it gain an overall mobility advantage over the enemy. The commander may want to yield ground quickly to make the attacking enemy commander think that the attacking enemy force has been successful or to entice the attacking enemy force to move to a decisive point where the striking force can attack. Normally, in a mobile defense, the commander retains ground only to facilitate the commitment of the striking force.

8-31. When conducting a mobile defense, the commander may need to commit the reserve to reinforce the fixing force and help shape the battlefield. The commander positions the reserve so that it effectively reacts to the most likely contingency and the enemy’s most dangerous COA. Without a reserve, the commander assumes significant risk in attempting to shape the enemy penetration. Circumstances may also force the commander to employ elements of the striking force to assist the fixing force. If that occurs, the commander uses available long-range fire support assets and attack helicopters. They are the best choice because of their ability to rapidly disengage and shift their effects to support the rest of the striking force on its commitment.


8-32. The commander’s situational understanding is critical in establishing the conditions that initiate the striking force’s movement and in determining the general area that serves as a focus for the counterattack. Situational understanding includes identifying those points in time and space where the counterattack proves decisive. A force-oriented objective or an EA usually indicates the decisive point. The staff synchronizes the unit’s activities in time and space to sufficiently mass the effects of the striking force at the right time and place.

8-33. The actions of the striking force are the echelon’s decisive operation on its commitment. The commander’s reconnaissance and surveillance assets focus entirely on tracking the enemy’s advance. The striking force commander continuously receives intelligence and combat information updates that allow that commander to adjust the counterattack as necessary to defeat the targeted enemy. Once the enemy force starts its attack, any forward-deployed elements of the striking force withdraw to assembly areas or attack positions and prepare for their commitment.

8-34. The defending commander launches the striking force in a counterattack when its offensive power, relative to that of the targeted attacking enemy element, is the greatest. (See figure 8-5.) Piecemeal commitment of the striking force in support of local objectives jeopardizes the success of the overall operation. The striking force must execute the counterattack rapidly and violently, employing all combat power necessary to ensure success. The striking force may be committed at a different time than anticipated and in an entirely different area than planned. Thus, it must be able to respond to unexpected developments rapidly and decisively.


Figure 8-5. Mobile defense after commitment of striking force

8-35. Because the striking force normally attacks a moving enemy, it generally assumes a combat formation with a covering force, an advance guard, a main body, and either a follow-and-support or a follow-and-assume force. The striking force takes advantage of obstacles, such as rivers or obstacle zones, that block the enemy’s movement. The strike force commander designates flank responsibilities and may even allocate a force against a particularly vulnerable flank. However, the striking force moves quickly and takes risks on its flanks, using its speed of movement and superior situational understanding to provide security.

8-36. The striking force attacks in a formation that provides maximum combat power forward to devastate the enemy force and achieve decisive results. The striking force takes advantage of its mobility and fire power to seize the initiative by overwhelming the enemy force with swift, violent blows that cripple the enemy’s command and control system, disrupt attacking enemy formations, and destroy enemy combat systems. The commander ensures that fire support and fixing force efforts capture the enemy’s attention and posture the enemy for attack by the striking force. During the counterattack, the strike force commander may have one element of the striking force occupy support by fire positions to suppress the enemy, while another striking force element prepares to assault the objective. Armored, Stryker, and infantry forces may make this assault. (Chapter 3 discusses the actual conduct of an assault on an objective.)

8-37. Engineers should be well forward to enhance the mobility of the striking force. These lead engineers search for existing obstacles and clear the route as much as possible within their capabilities. Follow-on engineers expand breaches, improve routes, and replace assault bridges with more permanent structures. Engineers with flank units focus on countermobility to protect the striking force’s flanks.


8-38. Commanders use defensive actions to create the opportunity to transition to the offense. In a mobile defense, that transitional opportunity generally results from the success of the striking force’s attack. The commander exploits success and attempts to establish conditions for a pursuit, if the result of the commander’s assessment of the striking force’s attack shows that there are opportunities for future offensive actions. (Chapters 4 and chapter 5 discuss exploitation and pursuit.) If the mobile defense is unsuccessful and the enemy retains the initiative, the commander must either reestablish a viable defense or conduct retrograde operations. (Retrograde operations are the topic of chapter 9.)

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