APPENDIX C
CROSSING MEANS
GENERAL
A safety matter that affects operational use is the load capacity of rafts, bridges, and equipment. The quantities shown in Table C-1 are the normal capacities or the design capabilities. In exceptional circumstances, certain safety factors or margins allow an increase in the load. These capacities have been deliberately omitted here because they are not intended for use in operational planning. The standard or design capabilities are provided for normal crossings. The exceptional category is intended for special situations using the terms caution or risk crossings.
In addition to the command decision required to employ caution- and risk- crossing loads, commanders must consider the physical status of the equipment. Thus, crossing-area or crossing-force commanders obtain a professional judgment from an engineer. The commander weighs these factors with the tactical needs before directing an increase in the load, keeping in mind that the equipment may be lost for future use. River crossings have three categories:
- Normal crossing-the vehicle's classification number is equal to or less than the bridge's, vehicles maintain 30-meter intervals on fixed or floating bridges, and the vehicle's speed must not exceed 24 kph. Sudden stopping or acceleration is forbidden.
- Caution crossing-vehicles with a classification exceeding the capacity of the bridge by 25 percent are allowed to cross under strict traffic control. The caution classification number of standard fixed or floating bridges may be obtained from FM 5-34, TC 5-210, or other appropriate technical manuals (TMs). The crossing requires that vehicles remain on the centerline and maintain 50-meter intervals. The crossing requires that vehicles do not exceed 13 kph, stop, accelerate, and shift gears.
- Risk crossing-may be made only on standard, prefabricated fixed and floating bridges and in the greatest emergencies. The vehicle moves on the centerline and is the only vehicle on the bridge. The crossing requires that vehicles do not exceed 5 kph, stop, accelerate, and shift gears. The vehicle's classification number must not exceed the published risk classification for the bridge type being crossed. After the crossing and before other traffic is permitted, the engineer officer reinspects the entire bridge for any damage.
DESCRIPTIONS OF CROSSING MEANS
Available crossing means dictate both crossing operations and the force-buildup rate on the far shore. Before the commander develops his tactics, he must understand how the available crossing means impact his ability to mass forces on the far shore .
The following are the crossing means that the military use to cross a river:
FORDING VEHICLES
Combat vehicles can ford shallow rivers that have a limited current velocity and stable beds. Some vehicles have kits to increase fording depth. Fording is possible for current velocities that are less than 1.5 MPS. Riverbeds at fording sites must be firm and free of large rocks and other obstructions. Vehicle-operator manuals contain specific depth capabilities and required adaptations. The AVLB and Wolverine can be used to assist fording vehicles in deep water.AMPHIBIOUS VEHICLES
Some combat vehicles can swim. Bank entry and exit points must be clear of obstructions and have slopes consistent with the vehicle's capabilities. The current's velocity sets limits. Crews of amphibious vehicles prepare and inspect each vehicle before entering the water. Engineer assistance, including recovery vehicles and standing cables, maximizes swimming opportunities.AIRCRAFT
Army aircraft are the primary crossing means for dismounted infantry. Helicopters also lift other crossing assets from rear areas to the river and carry essential combat support and critical resupply across it. See Table C-2 for characteristics of external loads for aircraft.BOATS
Pneumatic assault boats are the alternate crossing means for dismounted infantry and accompanying elements. For light infantry, assault boats may be the only means required if air resupply is available. They carry 12 assault troops and a two-man engineer crew in a silent or powered crossing.ASSAULT LAUNCHED BRIDGES
The AVLB is an organic engineer asset that travels with maneuvering armored and mechanized infantry formations and can quickly gap up to 15 meters for 70 MLC vehicles. The assault launcher can launch the bridge without exposing bridge personnel to enemy fire and can retrieve the bridge from either end (seeFigure C-1 and Table C-3).
The Wolverine will eventually replace the AVLB. The Wolverine will consist of an M1- series Abrams tank chassis modified to transport, launch, and retrieve a MLC 70 bridge. The bridge will be capable of spanning at least a 24-meter gap (see Figure C-2 and Table C-4).
RAFTS
Heavy rafts are often the initial crossing means for tanks and other fighting vehicles. They are faster to assemble than bridges and can operate from multiple sites to reduce their vulnerability. The two types of heavy rafts in the Army system are the ribbon and M4T6 (see Figures C-3 and C-4 and Tables C-5 through C-9). The ribbon raft is fielded to engineer units while the M4T6 is maintained in war stocks only.BRIDGES
Rafts alone cannot handle the total volume of traffic in the needed time. Floating bridges are the primary means to cross the force and its supplies rapidly. The same units that provide heavy rafts also provide float bridges. They often assemble bridges from the rafts used earlier.The ribbon bridge is the primary assault bridge because it is quick to assemble (see Figures C-5 and C-6 and Tables C-10 and C-11). The M4T6, currently maintained in war stocks only, would replace the ribbon bridge to allow the ribbon bridge to continue to move forward with the advancing force. Because it is man-power intense, the M4T6 is slower to assemble than the ribbon bridge (see Figure C-7 and Tables C-12 and C-13). Preassembly of the M4T6 floats in rear areas significantly reduces the final assembly time on the river.
Fixed bridges rest on the riverbanks and intermediate supports instead of floating on the water. They span ravines as well as rivers. They have limited use for the initial assault because they are slow to assemble and vulnerable to enemy action. Where appropriate, fixed bridges supplement or replace float bridges. Engineers also use fixed bridges to repair existing damaged bridges.
The rapid construction characteristics of the MGB versus the Bailey bridge provide it with a better capability that can be used well forward in the main battle area. Since the Army does not currently have a tactical dry-gap capability longer than 60 feet, using the MGB in this role becomes an important operational consideration (see Figures C-8 and C-9 and Tables C-14 through C-18). The primary role of the MGB is for tactical bridging in the brigade area, while the Bailey bridge is used primarily as a LOC bridge. As the tactical situation permits, the MGB is removed and replaced by Bailey, timber, or steel bridges.
The Army is currently in the process of developing the HDSB to replace the MGB. The HDSB provides tactical bridging for a gap-crossing capability of 40 meters without intermediate supports for wheeled vehicles up to MLC 96 and tracked vehicles up to MLC 70 (see Figures C-10 and C-11).
The M2 Bailey bridge is a truss bridge manually assembled by connecting panels end to end. It is used in forward areas to replace assault bridging and the MGB. The Bailey bridge system is highly labor intense but also highly versatile. In some cases, the Bailey bridge is the only tactical bridge suitable for long spans and heavy loads because it can be assembled in multiple heights and widths. The Bailey bridge is maintained in war stocks both in the US and outside continental US (OCONUS). The bridge system can also be assembled as a railway bridge, thus providing a relatively rapid-repair capability (see Figure C-11 and Table C-19).
In arctic regions and areas that experience seasonal winter weather, a consideration that cannot be overlooked is "ice bridging". Ice bridging is the use of bridging over a thick layer of ice that covers a wet gap, such as a lake or river (see Figures C-13 through C-15 and Tables C-20 through C-23).
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