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This chapter describes only those tactics and techniques used by a division in a retrograde river-crossing operation that are different from those used in an offensive crossing. A retrograde crossing features centralized control at division level. Detailed planning and preparation of engineer assets are a critical consideration within the time available. A retrograde crossing differs from an offensive crossing in several aspects:

• Both banks of the river initially are under friendly control. Accordingly, detailed information concerning the river and the area over which the retrograde is conducted should be readily available to the commander.
• All existing bridges and other crossing sites are available to the retrograde force to expedite the crossing.
• Relative combat power favors the enemy in most cases. Units conducting retrograde operations then must retain a mobility advantage over the enemy.

Deception is always planned and executed to deceive the enemy and to protect the force during a retrograde operation. As a minimum, these plans seek to conceal the extent of the operation and the actual crossing sites. Smoke, electronic deception, and dummy sites reduce the enemy's capability to disrupt the crossing.

The same control measures are used in retrograde operations as in offensive operations. Figure 6-1 shows an example. See Chapter 3 for a discussion of each control measure and a C2 diagram.

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DELAY

• Multiple approach routes from battle positions to crossing sites.
• Lateral routes between crossing sites.
• Alternate crossing sites if enemy actions close primary sites.
• Crossing equipment held in reserve to replace losses or open alternate sites.
• Preplanned engagement areas (EAs) to block enemy advances.

A delay combined with a retrograde river crossing has the following phases:

• Delay.
• Crossing.
• Defense.

Each phase is separate only in planning; they overlap during execution. Employing military crossing equipment in the retrograde is the reverse of the method used in a deliberate, offensive river-crossing operation. Figure 6-2 relates the retrograde sequence to the crossing stages.

DELAY PHASE

The division commander establishes a holding line on defensible terrain between the river and the enemy. Its location precludes direct and observed indirect fires in the crossing area.

Forces not assigned tasks in the delay, including those forces with a mission to support crossing areas or establish the defense on the exit bank, execute a planned retirement or withdrawal and cross the river as rapidly as possible. To preclude early enemy detection of the retrograde, the forces follow a movement-control plan that supports the deception plan.

The delay phase continues until the battle is within communications and fire-support range of the exit-bank defense. The delaying force must be strong enough to hold the enemy until other forces establish the defense. The defending force assumes responsibility for the battle as the delaying force completes a rearward passage of lines through the defending force.

Figure 6-3 shows an example of a retrograde crossing. In this case, the 3rd brigade is the delaying force. It occupies battle positions to the rear of the 1st and 2nd brigades at RL Plum, the initial-delay position (IDP), to help them withdraw. The 3rd brigade delays the enemy forward of the holding line until the rest of the division crosses the river and the 1st and 2nd brigades reestablish the defense along the river.

CROSSING PHASE

The commander should attempt to salvage tactical bridges and rafts for future use; however, it may be necessary to use them for the crossing and then destroy them to prevent capture. Fixed bridging must be prepared for destruction and also be protected against ground and air attacks. This requires close coordination with the delaying force to preclude cutting off friendly forces or allowing enemy seizure of sites intact.

The BMAIN, commanded by the brigade XO (CAC), is responsible for the passage of all units through the crossing area.

Traffic control up to and through the crossing area is a critical problem in crossing operations. For this reason, plans for movement must be detailed, and movement control is essential. This control is exercised by the CAC with assistance from the delaying-force commander (brigade commander). The CAC controls all movement within the crossing area to include retrograde forces.

It is the responsibility of the CAC to ensure the continuous and orderly flow of the retrograde elements across the river. His control includes both the ERPs, which ensure that all vehicles are of the proper class and size, and also all waiting areas that feed vehicles through the crossing area. To assist the CAC, MP and, if available, engineers establish and operate TCPs to manage the traffic flow. CSCs oversee the crossing means. The CAC and his staff must synchronize the crossing plan with the commander's tactical plan.

Activity within the crossing area begins with two-way crossings by CSS units evacuating nonessential supplies or restocking the delaying force. During the early stages of the retrograde, the existing crossing means may be supplemented by tactical bridging. As a minimum, additional tactical bridging assets must be planned and available.

Initially, the force crosses on fixed and floating bridges. It crosses on bridges as long as possible, since this is the most rapid means. Once the bridges become vulnerable to capture, air attack, or observed indirect fires, they may be converted to rafts or removed. Vehicles continue to cross by using rafts or by swimming. The crossings are made under the suppressive fires of the defending force's direct- and indirect-fire weapons.

The forces cross the river in an orderly flow while conserving combat power. The retrograde crossing begins as a rear-area operation for the division. Initially, it is a traffic-scheduling problem, centrally controlled by the division. The division establishes crossing areas before crossing maneuver brigades. Crossing-area operations are the same as for offensive crossings (see Chapter 5). Even when the division has to establish the crossing areas quickly, under adverse circumstances, it synchronizes crossing-support activities with those of the defense force that is preparing to close the routes in the crossing areas.

Crossing sites need the highest priority for AD. This is particularly critical when the enemy has air superiority or when air parity exists. The sequence for crossing AD units should account for the need to provide continuous coverage of crossing sites.

The division engineers are fully committed to the delay. As a result, engineers under the control of the CAE run the crossing sites and support initial preparation of exit-bank defenses. Engineers focus on enemy engineer breaching assets and the interdiction capabilities needed to support enemy maneuver.

DEFENSE PHASE

Initially, the defending force is small. It consists of combat and combat-support units not involved in the delay as well as augmentation from corps reserves. Because enough forces are not available to defend all points along the river, the defense depends on rapid lateral movement to concentrate at vulnerable points. In particular, it orients on and protects the crossing sites against the enemy's forward detachments and heliborne forces.

After battle handover from the delaying force, the defending force is responsible for the area between the holding line and defensive positions on the exit bank. The defending force masses fires to help its elements in contact forward of the river to withdraw, thereby complicating the retrograde crossing.

The defending force accepts battle hand-over from the last of the delaying force at the holding line and covers its crossing over a fixed bridge that is prepared for demolition. Friendly forces at the river prevent the enemy from crossing at the site of a demolished fixed bridge so that companies securing the crossing site can safely withdraw in turn.

WITHDRAWAL

During a withdrawal, the enemy usually does not pressure withdrawing units. Also, other friendly units do not normally assist in withdrawals. Care must be taken to ensure that the enemy does not try to isolate and encircle units during river-crossing operations. If a unit has difficulty breaking with the enemy in a withdrawal, it can request help from a higher level. The assisted withdrawal will be a rearward passage of lines. Exchange of information on obstacles, indirect-fire targets, and routes in the sector must be coordinated before conducting the passage of lines. The assisting unit provides mobility support along cleared routes and corridors in its sector for the passing unit.

Engineers must complete clearing operations before the passage begins. The assisting unit also closes the lanes once passage is complete. The passing unit must plan and organize for conducting internal breaching and river-crossing operations before initiating the passage of lines. This should ensure responsive mobility operations if the enemy blocks routes during the passage.

RETIREMENT

The laws of war require that denial operations, particularly against civilian resources such as existing bridges, be carefully considered and that execution authority to destroy the structure be maintained at the highest level.

A defending-force commander is responsible for preparing existing bridging and other crossing means in his sector, such as ferries, for destruction to prevent their use by the enemy. The CAE controls the engineers who prepare those targets. The timing of their destruction depends on their use in supporting the crossing. When the tactical situation dictates that crossing sites are no longer needed or the risk of capture outweighs their usefulness, the defending force must destroy them.

Use of bridges in the retrograde requires a redundant means of bridge destruction and a robust demolition guard with an engineer demolition party (see FM 5-250). Engineer light diving teams can be used to survey and emplace, prime, and detonate explosives on bridge supports to deny enemy access during retrograde operations. Because of the severe consequences of a premature decision to destroy a site, the division commander usually designates sites as reserve targets and issues specific orders stating under what conditions and by whose authority this destruction can be done.

Engineers destroy military bridges that they cannot recover quickly. Bridge stocks are in short supply; therefore, if existing bridges are sufficient to support the retrograde, the engineers recover military bridges early. In addition, the denial of major existing bridges can be so important that the commander may choose to destroy them early and rely on military bridges to cross the remainder of his force. The ribbon bridge is preferred for this crossing because of its recovery speed. Engineers either recover lines of communication (LOC) bridges well before the enemy arrives or destroy those left in place after the delay.

The commander uses deception to conceal the extent of the operation and the actual crossing sites. Smoke, electronic warfare, and dummy sites reduce the enemy's capability to disrupt the crossing. OPSEC keeps the enemy-intelligence collectors from identifying the time and place of the crossing. The commander may consider retaining fixed bridges in defense of the river line if he anticipates future counterattacks back across the river. He may also partially destroy bridges to ease restoration in future offensive operations, weighing this decision against the enemy's use of the bridges.

Denial operations are somewhat restrictive. Only those civilian targets with a clearly identified military value can be destroyed or removed. Coordination between the theater command and the host-nation government is important in the policy-development process.