CHAPTER 7
CROSSING SITES
GENERAL
- Existing situation and anticipated scheme of maneuver.
- Physical characteristics of the available sites, road networks, and surrounding terrain.
- Availability and capabilities of crossing means.
- Availability of engineer support.
Conflicts between tactical and technical requirements frequently occur. Commanders evaluate the factors bearing on the problem to determine the best overall solution.
CROSSING-SITE SELECTION
Both the desired scheme of maneuver and available crossing means influence crossing-site selection. The division assigns a crossing area to each lead brigade. The brigade chooses which crossing sites to use within its area. When a particular site is important to the division's tactical concept, such as for the movement of breakout forces, the division either coordinates with the affected brigade to open that bridge site or moves a bridge to that site once the brigade hands over the crossing area to the division.
Brigade commanders select final crossing sites based on tactical intelligence and their desired schemes of maneuver. Each site's physical characteristics, required engineer support, and available crossing means influence the decision, but tactical requirements are the most important.
The goal when selecting assault sites is to pick those that allow the lead battalions to cross unopposed and seize far-shore objectives rapidly. If unsuccessful at finding undefended crossing sites, the lead battalions cross under enemy fire while overwatch units provide direct and indirect suppressive fires. Assault sites may or may not coincide with rafting or bridging sites.
When selecting swimming sites, the goal is to pick those that permit fighting vehicles to rapidly enter, swim across, and exit the water with minimum assistance.
The goal when selecting rafting and bridging sites is to pick those that support the greatest volume of vehicle traffic consistent with the scheme of maneuver. Rafting and bridging sites are usually on or near major roads to minimize route preparation and maintenance. When the sites are located close together, the bridging site must be upstream of the rafting site. This will avoid potential damage that may be caused by disabled rafts drifting into the bridge.
Regardless of the crossing means, each site needs engineer reconnaissance swimmers or an engineer light diving team to cross early, reduce obstacles, and develop exit points on the far bank. Riverbanks at otherwise suitable crossing sites often need work for access to the river. Most natural soil becomes unstable under heavy traffic. This condition worsens as fording, swimming, and rafting activities carry water onto it. The required engineer effort varies with soil type, crossing means, and vehicle density. An engineer vehicle that is capable of maintaining the exit bank should be one of the first vehicles across.
Natural conditions vary widely. Banks may require little preparation, or they may be so restrictive that they limit feasible sites. Desirable site characteristics include-
- Minimum exposure to enemy direct-fire weapons.
- Covered and concealed access to the river's edge.
- Firm and gently sloping banks that allow rapid entry and exit at multiple points.
Initial and subsequent entry points can vary. Available locations seldom have all the desired tactical and technical characteristics. The best routes through the crossing area normally cross the river at the technically best crossing sites. The best technical sites may not be the best tactical sites because they are well known and are heavily defended by the enemy. Forces initially crossing at less desirable locations are most likely to avoid detection and gain surprise. Moving laterally along the exit bank, forces attack the flank or rear of enemy units to seize the better crossing locations. Use of these sites allows rapid buildup of combat power.
PLANNING
- Friendly and enemy capabilities and probable COAs.
- Site capacity for the crossing of troops, equipment, and supplies using various crossing means.
- Engineer support that is required to develop, improve, and maintain each site.
More specifically, planners need to know the-
- Condition of the bottom, banks, and water of the river.
- Impact of forecasted or past seasonal weather conditions.
- Location of defensible terrain, covered and concealed areas, and natural or enemy-emplaced obstacles on both sides of the river.
- Amount of time and effort that is required to develop sites, assemble rafts, and construct bridges.
- Entry/exit routes and off-road trafficability.
- Road networks.
- Capabilities of friendly forces to deny observation, suppress fires, and provide site protection.
REQUIREMENTS
ENTRY/EXIT ROUTES OR PATHS
A desired feature of all sites is readily accessible entry/exit routes or paths on either bank. The approaches to the banks are checked for their ability to support the requirements (width, slope, and trafficability) of the wheeled and tracked vehicles of the crossing element. Covered and concealed approaches enhance surprise and survivability; however, multiple routes, free from obstruction, will increase crossing speed and flexibility. Exit-bank conditions often take precedence over entry-bank conditions until equipment and troops can be crossed to develop and improve the site. See Table 7-1 for depth requirements.

ROUTES AND APPROACHES
Depending on the crossing operation that is used, the following considerations must be given to routes and approaches:
- Fording. Dismounted forces may use approaches with steep slopes and heavy vegetation, while vehicle fording requires paths or roads to approach fording sites.
- Assaulting or swimming. Assault-boat crossings may use more rugged approaches than amphibious vehicles.
- Rafting. Multiple approach routes to rafting sites permit the relocation of rafting upstream or downstream.
- Bridging. Bridging sites require developed road networks to sustain the crossing capacity.
Depending on the vehicle that is used, the following considerations must be given to routes and approaches:
- Wheeled vehicles. In general, wheeled vehicles require 3.5-meter path widths and 3.5 meters of overhead clearance. Dry, hard slopes of 33 percent can be negotiated; however, slopes less than 25 percent are desired.
- Tracked vehicles. Tracked vehicles require up to 4-meter path widths and 3.5 meters of overhead clearance. Tanks can climb 60 percent (31-degree) slopes on dry, hard surfaces; however, slopes less than 50 percent are desired.
WAITING AREAS
Numerous waiting areas are required for equipment and troops preparing and protecting sites and for troops and vehicles preparing and/or waiting to cross. These areas should be dispersed, provide cover and concealment, and be accessible to road networks near the sites.
RIVER CONDITIONS
In general, currents less than 1.5 meters per second (MPS) are desired. Narrow segments of the river decrease equipment requirements, crossing time, and exposure time. However, resulting increased current velocities may offset any advantage. As the current's velocity increases, it decreases the ribbon bridge's ability to handle heavy military load class (MLC) vehicles. More boats will be required to keep the bridge in place and allow for heavy MLC vehicles to cross.
BANKS
Ford banks may be steep and rugged for dismounted troops; however, vehicles require slopes less than 33 percent and firm soil conditions. Assault or swim banks may be steep when using assault boats for dismounted troops. Amphibious vehicles may be able to enter over low, 1-meter vertical banks, but they require sloped exits. Vertical banks of about 1 meter may be accommodated by bridge or raft ramps (see Table 7-2). Vertical bank heights for bridges using the equipment listed in the table do not change for ribbon bridges. For M4T6 and Class 60 bridges, the height of the bridge deck can be adjusted to accept a difference in bank heights; however, the limiting factor may become the longitudinal slope of the bridge.

BOTTOMS
Ford bottoms must be free from obstacles, firm, and uniform. Riverbeds may be improved with rock fill or grading equipment. Guide stakes make the crossing of the river easier for boat drivers. Assault- or swim-site bottoms must be free from obstructions that interfere with boats or the tracks of amphibious vehicles. Rafting sites must be free from obstructions that could interfere with boat operations. Bridges emplaced for lengthy periods (4 hours or more) or in strong currents require suitable riverbeds for anchorage. Engineer light diving teams from the corps Army may be used to-
- Conduct river-bottom reconnaissance.
- Emplace shore and midstream anchorage for debris and antimine and antidiver nets to ensure the success of the operation.
ENEMY SITUATION
Sites masked from enemy observation enhance surprise and survivability by degrading the enemy's ability to see. Using existing sites reduces preparation time but requires caution in that the enemy may have emplaced obstacles and registered artillery on the site.
SITE ANALYSIS

FIELD CALCULATIONS
- Measuring the current's velocity.
- Determining slopes and degrees.
- Measuring the river's width.
- Calculating downstream drift.
MEASURING THE CURRENT'S VELOCITY
Correlating the desired maximum current velocity of 1.5 MPS with a familiar comparative unit of measure may help in estimating the current's velocity. The quick-time march rate of 120 steps per minute, with a 30-inch (or 76-centimeter) step, equates to 1.5 MPS. Other approximate correlations of 1.5 MPS include-
Determining the current's velocity is critical to effective and safe crossing operations. When it is high, more boats are required to stabilize the bridge, particularly when anchorage is not used. A reasonable estimation involves measuring a distance along the riverbank and noting the time a floating object takes to travel the same distance. Dividing the distance by the time provides the current's velocity (see Figure 7-2).

DETERMINING SLOPES AND DEGREES
The slope of terrain is significant (for example, slopes of 7 percent or more slow movement and may require vehicles to operate in a lower gear). Slope, usually expressed as a percentage, is the amount of change in elevation (rise or fall) over a ground (horizontal) distance (see Figure 7-3).
- Clinometers. These instruments measure the percent of the slope and are organic to most engineer units down to the platoon level.
- Maps. In this method, first measure the horizontal distance along the desired path, then determine the difference in elevation between the starting and ending points of the path. The next step is to ensure that both figures are the same unit of measure (such as meters or feet). The final step is to divide the elevation (rise) by the distance (run) and multiply the result by 100 to get the percent of the slope (see Figure 7-4).


MEASURING THE RIVER'S WIDTH
A field-expedient means of measuring the river's width is with a compass. While standing at the waterline, fix your sight on a point on the opposite side and note the magnetic azimuth. Move upstream or downstream until the azimuth reading to the fixed point on the opposite bank is 45 degrees different than the original reading. The distance from the original point to the final point of observation is equal to the river's width (see Figure 7-6).
CALCULATING DOWNSTREAM DRIFT
Current causes all surface craft to drift downstream. Each vehicle has a different formula for calculating downstream drift. Amphibious vehicles and assault boats drift more than powered boats and rafts; the latter has a greater capability to negate the effect of the current's velocity by applying more power.
Example 1
Entry is usually made upstream of the desired exit point. The vehicle or boat is aligned, or aimed, straight across the river, creating a head-on orientation that is perpendicular to the exit bank. However, the current produces a sideslip, downstream forward movement (see Figure 7-8). This technique requires operator training in continual adjustment to reach the objective point on the exit bank. This technique results in a uniform crossing rate in the least amount of time and is usually the desired technique.
Example 2
If the operator continues to aim the vehicle at the desired exit point, the orientation of the craft at the exit point will approximate an upstream heading. The craft's path is an arc in proportion to the current's velocity (see Figure 7-9).
Example 3
To exit at a point directly across from the entry point requires an upstream heading to compensate for the current's velocity (see Figure 7-10).
In all three examples, the craft's speed relative to the current's velocity is constant, assuming the engine revolutions per minute (rpm) or paddling rate remains constant.
RAFTS
- Are less vulnerable to enemy air and indirect fire due to their size and maneuverability.
- Are quicker to assemble.
- Offer more flexibility in operation, particularly in site selection and subsequent movement between sites.
- Can use existing road networks and banks where access and exit routes are not aligned opposite of each other.
SITE PREPARATION
The brigade commander also decides when bank preparation can begin, or he may delegate this decision to his CAE. The decision is based on the estimated time required to secure the area. By initially spending extra time and effort preparing a bank, maintenance problems can be avoided during rafting operations.
The key to rapid and effective bank preparation is good engineer reconnaissance, which permits engineers to arrive at the site early, organized and equipped to perform specific tasks to improve the approach. The same is true on the exit bank. Poor bank conditions require early priority for raft movement of engineer equipment across the river. Time spent preparing the exit banks before passing heavy traffic greatly reduces maintenance of the crossing site and speeds force buildup later. Two entry and exit points per centerline make it possible to alternately use one while maintaining the other.
RAFTING SITES
Each lead brigade should have at least two rafting sites, each of which has one to three raft centerlines. The terrain, routes, and tactical plan determine their location. However, they should not be closer together than 300 meters to avoid congestion and the risk that enemy artillery concentrations will impact on more than one site during a barrage. Engineers prepare alternate sites as soon as possible to permit the relocation of rafts in case of enemy action or bank deterioration. Each rafting site also contains the control and operation structure that is necessary to conduct rafting operations (see Figure 7-11).

- Raft-guide markers, at a 45-degree angle upstream, are used to guide the raft to the embarkation or debarkation point. The two markers are 91 centimeters apart, and the marker farthest from the river is 60 centimeters higher than the other. The raft has the correct approach to the bank when the markers appear to be in a straight line, with one above the other.
- Raft-landing markers depict the left and right limits of the embarkation or debarkation point.
- Vehicle-guide markers are used to align raft loads with the raft and are visible to both the raft and the vehicles.

- A bridge boat to move damaged bays and serve as a spare boat.
- A crane to remove nonrepairable equipment from the water.
- A bridge truck to transport damaged equipment to the EEP.
- A fuel heavy-expanded mobility tactical truck (HEMTT) to refuel boats.
- One or more interior and exterior bays to use as replacement parts. The maintenance area is continuously manned with-
- Two mechanics with tool boxes.
- Two fuel handlers.
- The operators of the various pieces of equipment.
- A site supervisor.
RAFTING OPERATIONS
Units begin their preparations for rafting operations at a staging area. There, they receive briefings, conduct inspections, and rehearse the rafting operation. Personnel will be issued life jackets and given instructions on what to do upon loading onto the raft.
When ordered to begin rafting, the site commander directs personnel at the ERP in the call-forward area to begin sending raft loads forward. Units proceed from a staging area to the call-forward area where engineers at the ERP organize them into raft loads and send them down to the river. Any points along the route that may cause confusion, such as intersections, are either manned with a guide or are marked to ensure that the vehicles do not get lost. Once a raft load nears the river, the platoon leader directs it to the appropriate centerline. The platoon leader controls the flow of traffic to the centerlines to ensure that there is a smooth flow of traffic and that centerlines are neither congested nor underused. He establishes the timing required so that raft loads leave the call-forward area and match up with a returning empty raft.
When a raft load reaches the riverbank, it is met by an engineer centerline guide. He stops the raft load 3 meters from the edge of the water and holds it there for the raft commander. The raft commander guides the vehicles of the raft load onto the raft. The raft crew chocks the vehicles and ensures that all passengers are wearing life jackets. The passengers do not dismount from their vehicles. All hatches are opened to allow quick exit of the vehicle in case of an emergency. Upon reaching the debarkation point, the raft commander guides the vehicles off the raft. After the raft load debarks, the raft commander checks with the centerline guide for any return vehicles and returns to the embarkation point.
Once on the far shore, the centerline guide directs the raft load to the far-shore holding area where it re-forms. The passengers remove their life jackets, which are collected and returned by an engineer team to the staging area for future loads.
MAINTENANCE AND REFUELING
During rafting operations, rafts require stops for refueling, preventive maintenance, and minor repairs. The efficiency of the crossing depends on all rafts having enough fuel and minimal lost time for refueling and normal maintenance. This efficiency requires the bridge company to intensely manage raft maintenance and to operate the maintenance area much like a pit crew in an automobile race. When directed, a raft pulls off the centerline and moves to the crossing-site maintenance area.
With the raft secured, the crew begins refueling and maintenance operations. Mechanics assess and repair any minor damages to the raft and the boats. Fuel handlers run fuel lines from the fuel to both bridge boats and fuel them simultaneously. If no major deficiencies are identified, the entire process requires 20 minutes. If major deficiencies are identified on the boat, it is removed from the raft and replaced with an awaiting spare. The boat will then be removed from the water and sent back to the EEP for repair. When refueling and maintenance operations are finished, the raft returns to its centerline and another raft is directed in for maintenance and refueling.
Since the maintenance and refueling operation is continuous and requires removing a raft from the operation for up to 30 minutes, it is important to account for this reduction in capabilities when planning the operation. Generally, it is unnecessary to refuel for the first two hours after rafting begins. Once raft maintenance and refueling begin, one of the six rafts in each bridge company is unavailable for carrying vehicles across a river at all times.
When a raft becomes damaged and needs immediate repair, the raft commander moves it to the maintenance area. If a raft loses a boat and cannot make it to the maintenance area without assistance, the raft commander contacts the maintenance supervisor, who sends the maintenance boat out to assist. If a raft is still carrying a load, the raft commander decides on which bank he will disembark the load. Once in the maintenance area, mechanics determine the extent of the damage. If the damage requires significant repair, the raft will be removed and replaced with a spare. Lengthy equipment repairs are done at the EEP.
BRIDGES
Bridges need protection. AD, counterfires, and ground-security elements are necessary to defeat enemy attacks. Booms on the river protect bridges from damage caused by waterborne munitions and debris. Antidiver nets are placed upstream and downstream to protect bridges from swimmers or underwater demolition teams. Engineer light diving teams may be employed to reduce debris along the debris-collection side of the upstream boom using portable hydraulic chain saws.
Bridges are vulnerable to enemy long-range artillery fire and air attack even after the assault force clears enemy forces from the exit bank. For this reason, ribbon bridges are used for a limited period of time, normally two to four hours, before engineer bridge units break them apart and move them to other sites. When the division uses this pulse-bridging tactic, its units wait to cross in staging areas and surge across when bridges are in place.
Enemy air superiority over the river may prohibit bridge assembly. A sustained enemy air attack forces engineers to break established float bridges into rafts. This minimizes the destruction of scarce bridging assets yet enables the crossing to continue, though at a slower pace. Engineers prepare alternate sites and position spare equipment nearby in case of enemy action.
As the danger from enemy action lessens, engineers use the more slowly assembled LOC and M4T6 bridges to augment and then replace the tactical bridges (ribbon bridge or AVLB). They do this as soon as possible to move ribbon bridges forward to other crossing operations.
Enemy bridges captured by the lead brigades are a bonus and speed the crossing. Engineers with the lead brigades neutralize explosive devices and reinforce weak or damaged bridge structures whether the damage is above or below the waterline. Commanders rarely base the success of an operation solely on the seizure of intact bridges.
SITE ORGANIZATION
A bridging operation requires a continuous traffic flow to the river. Units must be quickly briefed and moved to the crossing site. To accomplish this, units receive briefings in the staging areas from traffic-control personnel. There is no intermediate call-forward area. To control crossing vehicles, the engineers from the bridge unit set up an ERP at the bridge's access points on each side of the river. These engineers guide vehicles onto and across the bridge, ensure the proper speed and spacing of vehicles on the bridge, and prevent vehicles too heavy for the bridge from trying to cross.
A recovery team is stationed on the far shore to remove any damaged vehicles from the bridge. The recovery team consists of a medium or heavy recovery vehicle and crew, with sufficient winch cable to reach across the bridge. A typical site setup is shown in Figure 7-13. The bridge site must have several possible centerlines with adequate road networks from the unit's staging areas. Individual centerlines are spaced greater than 300 meters apart to reduce the effect of enemy artillery and air attacks.

Guides carry flashlights or chemical lights to guide the vehicles. The first guide momentarily stops the vehicle at the ramp and guides it onto the bridge. He then shields the lights with his body and steps out of the roadway. The second guide, spaced about 30 meters farther along the bridge, unshields his lights and directs the vehicle to his location. When the vehicle operator sees a guide shield his lights, he looks further down the bridge to pick up the next lights and is guided to them. When the vehicle reaches the guide, he shields his lights and steps aside so that the next guide can pick up the direction of the vehicle. This procedure is continued across the bridge.
NIGHT OPERATIONS
At night and during limited visibility, bridge company soldiers guide the vehicles across the bridge to prevent them from driving over its side and to help them to maintain the correct crossing speed.
Soldiers must not ground-guide vehicles by walking in front of them. Instead, soldiers should be placed as guides in stationary positions at reasonable intervals along the bridge.
ACTIONS UNDER FIRE
If the unit comes under fire while on the bridge, those vehicles that are on it continue moving to the other side and leave the area. Vehicles that are not yet on the bridge stop and go into a herringbone formation or take up concealed positions. Once all vehicles have cleared the bridge, the bridge crew will break it into rafts and disperse them to reduce their vulnerability to incoming fire. VEHICLE RECOVERY
If a vehicle breaks down on the bridge, the bridge crew will immediately attach a winch cable from the far side and drag the vehicle off the bridge. The recovery vehicle will not move onto the bridge and tow the disabled vehicle off since the critical requirement is to clear the bridge and maintain traffic flow; loss of the vehicle is far less important. OTHER GAP-CROSSING EQUIPMENT
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