Module 1
Bridging Fundamentals
Military bridging is the capability to establish crossing sites over gaps that impede military movement. Gap crossing operations are among the most complex engineer tasks, requiring precise coordination between engineer units, maneuver forces, and supporting elements.
Types of Military Bridges:
- Fixed Bridges: Permanent or semi-permanent structures that rest on abutments and piers. Include assault bridges, tactical bridges, and reinforcing bridges.
- Floating Bridges: Bridges supported by pontoons or floats that rest on water. Used when bottom conditions prevent fixed bridge construction.
- Ribbon Bridges: Modular floating bridge systems using interlocking bay sections. The Army's primary heavy floating bridge capability.
- Rafts: Floating platforms for transporting vehicles and equipment across water gaps when bridges are impractical or unnecessary.
Gap Classification:
- Wet Gap: Rivers, streams, lakes, canals — require floating bridges, rafts, or assault boats
- Dry Gap: Ravines, anti-tank ditches, wadis — require fixed bridges or assault bridging
- Anti-Tank Obstacles: Man-made or natural obstacles designed to stop armored vehicles
Bridge Classification Numbers:
Military bridges use a classification system based on Military Load Class (MLC). The MLC indicates the maximum load a bridge can safely carry:
- Tracked vehicles: MLC 4, 8, 12, 16, 24, 30, 40, 50, 60, 70, 80, 100, 120, 150
- Wheeled vehicles: MLC 4, 8, 12, 16, 24, 30, 40, 50, 60, 70, 80, 100, 120, 150
- M1 Abrams tank: MLC 68 (tracked)
- M2 Bradley: MLC 30 (tracked)
Bridge Reconnaissance:
Before any bridging operation, conduct thorough reconnaissance:
- Gap width and bank heights
- Water depth and velocity (for wet gaps)
- Bottom conditions and load-bearing capacity
- Approach routes and exit routes
- Concealment and defilade positions
- Enemy positions and observation
Gap Crossing Site Organization:
- Assembly Area: Units prepare equipment and receive final instructions
- Holding Area: Vehicles await their turn to cross
- Approach Marshaling Area: Vehicles organized by priority and classification
- Crossing Site: The bridge or raft itself, controlled by military police or engineers
- Exit Marshaling Area: Post-crossing reorganization point
Module 2
Fixed Bridge Operations
Fixed bridges provide the most efficient crossing capability when site conditions permit. They offer greater load capacity and stability than floating bridges and require less maintenance during operation.
Assault Bridges:
Designed for rapid emplacement under combat conditions to support initial assault forces:
- M60 Armored Vehicle Launched Bridge (AVLB): 60-foot span, MLC 60, launched from M60 or M48 chassis
- M104 Wolverine: Heavy assault bridge on M1 Abrams chassis, 26-meter span, MLC 70
- Joint Assault Bridge (JAB): Modern replacement, MLC 80 capability, 60-foot span
- Medium Girder Bridge (MGB): Modular bridge using aluminum girders, spans up to 49 meters
MGB (Medium Girder Bridge) Components:
- Panels: Primary load-bearing elements, connected with pins
- Chords: Top and bottom horizontal members of panels
- Webbing: Diagonal and vertical members connecting chords
- Transoms: Cross members supporting the deck
- Decks: Running surface for vehicles
- Rakers: Bracing members for stability
- Bracing Frames: Transverse bracing between panels
MGB Configurations:
- Single-Single (SS): One panel high, one panel wide — MLC 16, up to 9.6m span
- Double-Single (DS): Two panels high, one panel wide — MLC 50, up to 20.1m span
- Double-Double (DD): Two panels high, two panels wide — MLC 70, up to 31.4m span
- Triple-Single (TS): Three panels high, one panel wide — MLC 70, up to 30.8m span
- Triple-Double (TD): Three panels high, two panels wide — MLC 100, up to 49.4m span
MGB Construction Sequence:
- Site preparation and abutment construction
- Launching nose assembly (if using launching method)
- Bridge assembly on rollers or launching equipment
- Launch bridge across gap using rollers or cranes
- Remove launching nose and install end posts
- Install ramps and deck surfacing
- Install guide rails and traffic control devices
Bridge Reconnaissance Checklist:
- Gap width (face to face of abutments)
- Bank heights and slopes
- Soil bearing capacity for abutments
- Approach and exit route conditions
- Overhead clearance requirements
- Water flow characteristics (if wet gap)
- Enemy observation and fields of fire
Safety Considerations:
- Never exceed published Military Load Class
- Maintain proper vehicle spacing (minimum 30 meters)
- Control vehicle speed (maximum 15 mph on military bridges)
- Monitor bridge for damage during use
- Establish emergency bypass procedures
- Post bridge classification signs at both ends
Module 3
Floating Bridge Systems
Floating bridges provide crossing capability over water gaps where fixed bridges are impractical due to bottom conditions, depth, or tactical requirements. They rest on the water surface and adjust to changing water levels.
Floating Bridge Principles:
- Reserve Buoyancy: The bridge must have enough flotation to support the dead load plus live traffic loads
- Stability: The center of gravity must remain above the metacenter for stability
- Freeboard: Minimum distance from waterline to deck edge (typically 12+ inches)
- Deflection: Bridge must not sag excessively under load
Load Classification and Types:
- Dead Load: Weight of the bridge itself (pontoons, superstructure, accessories)
- Live Load: Weight of traffic crossing the bridge
- Impact Load: Dynamic forces from vehicle movement (typically 25% of live load)
- Wind Load: Forces from wind on bridge and vehicles
- Current Load: Forces from water flowing against the bridge
Current Effects on Floating Bridges:
- Current creates drag forces on the bridge structure
- Higher currents require more anchoring and stronger bays
- Maximum current for standard floating bridges: 6-8 feet per second
- Angle of bridge to current affects loading (ideal: 90 degrees)
- Upgrading required for high-current conditions
Water Gap Site Selection Criteria:
- Width — narrower gaps require fewer bays and less time
- Current velocity — lower is better for floating bridges
- Bank conditions — firm banks for anchoring and approaches
- Depth — sufficient for floating bridge draft
- Concealment — natural cover from enemy observation
- Access — good approach and exit routes
- Trafficability — ability to support anticipated traffic volume
Anchoring Systems:
- Shore Anchors: Deadman anchors, stake anchors, or equipment on shore
- Bottom Anchors: Concrete blocks, drag anchors, or screw anchors on river bottom
- Up-river Anchors: Prevent downstream drift
- Down-river Anchors: Control position and prevent overtopping
- Spring Lines: Control lateral position
Floating Bridge Components:
- Interior Bays: Standard bridge sections between ramp bays
- Ramp Bays: Transition sections at each end
- Deck: Running surface for vehicles
- Stringers: Support the deck
- Floats/Pontoons: Provide buoyancy
- Bracing: Transverse and longitudinal stability members
- Anchoring Hardware: Cleats, bollards, cable connections
Bridge Classification and Marking:
All floating bridges must display classification signs at both ends indicating:
- Military Load Class (tracked and wheeled)
- Maximum single-axle load
- Maximum speed limit
- Vehicle spacing requirements
- Bridge commander contact information
Module 4
M4T6 Float Bridge
The M4T6 Float Bridge is a lightweight, high-mobility floating bridge system used by engineer units for rapid gap crossing. It consists of aluminum-alloy interior and ramp bays that can be transported by standard military vehicles and emplaced by trained engineer squads.
M4T6 System Components:
- Interior Bay: Standard 18-foot section, weighs approximately 6,500 lbs
- Ramp Bay: End section with hinged ramp for bank transition
- Bolsters: Support structure connecting bays
- Beams: Longitudinal load-bearing members
- Floats: Pneumatic rubber floats providing buoyancy
- Decking: Aluminum running surface
- Anchoring System: Cables, winches, and shore anchors
M4T6 Technical Specifications:
- Normal Loading: MLC 16 (tracked and wheeled)
- Upgraded Loading: MLC 24 with supplemental flotation
- Interior Bay Length: 18 feet
- Ramp Bay Length: 20 feet (including ramp)
- Overall Width: 14 feet (single-lane)
- Freeboard (Normal): 16 inches minimum
- Maximum Current: 8 feet per second (with proper anchoring)
- Assembly Time: 4-6 hours for 100-foot bridge (trained crew)
M4T6 Transport and Launch:
- Transport: M939 5-ton truck carries one bay with float attached
- Launch Method: Bays are launched from trucks using rollers or cranes
- In-Water Assembly: Bays are connected in the water using pinning system
- Deck-Level Assembly: Bays are assembled on shore and launched as sections
M4T6 Construction Sequence (Wet-Emplacement):
- Conduct site reconnaissance and marking
- Position anchoring system (shore and bottom anchors)
- Launch first ramp bay from downstream bank
- Connect additional bays working upstream
- Install final ramp bay on upstream bank
- Secure all pinning and bolting connections
- Install and tighten anchoring system
- Install guide rails and traffic control devices
- Conduct proof load test and open to traffic
M4T6 Site Requirements:
- Bank Height: Maximum 8 feet for standard ramp bay
- Bank Slope: 1:3 or gentler for vehicle exit
- Bank Soil: Firm enough to support shore anchors
- Water Depth: Minimum 4 feet for float clearance
- Gap Width: Determined by number of bays available
- Current: Less than 8 fps for normal operations
Operating Procedures:
- Bridge commander controls access from both ends
- Maintain minimum 30-meter vehicle spacing
- Maximum speed: 15 mph (reduced in current or wind)
- Stop traffic during anchoring adjustments
- Monitor freeboard and deflection continuously
- Post sentries to observe bridge behavior
- Keep maintenance crew on standby during operation
Maintenance and Inspection:
- Inspect all pins, bolts, and connections before use
- Check float inflation and condition
- Verify anchoring system tension
- Monitor for unusual movement or noise during use
- Post-operation cleaning and component inventory
- Report all damage through proper maintenance channels
Module 5
Ribbon Bridge Operations
The Improved Ribbon Bridge (IRB) is the U.S. Army's primary heavy floating bridge system. It provides a continuous roadway across water gaps for heavy military traffic including main battle tanks. The modular design allows for rapid emplacement and high traffic capacity.
Improved Ribbon Bridge (IRB) Components:
- Ramp Bay: End section with hinged ramp, connects to shore
- Interior Bay: Standard 22-foot section, connects bays together
- Bay Coupling System: Mechanical connection between bays
- Power Pack: Hydraulic system for ramp operation
- Transportation Kit: Wheeled trailer for highway movement
- Launch/Retrieval System: Equipment for emplacing and recovering bays
IRB Technical Specifications:
- Normal Loading: MLC 80 (tracked and wheeled)
- Upgraded Loading: MLC 96 with supplemental equipment
- Interior Bay Length: 22 feet
- Interior Bay Width: 22 feet (dual lane)
- Ramp Bay Length: 29 feet (including ramp)
- Freeboard (Normal): 3 feet minimum
- Maximum Current: 6 feet per second
- Assembly Rate: 15-20 minutes per bay (trained crew)
IRB Transport Configurations:
- Truck Transport: M1977 CBT (Common Bridge Transporter) carries one bay
- Boat Mode: Bay can be powered by outboard motors for self-deployment
- Towing Mode: Bays can be towed in water by bridge erection boats
- Roll-on/Roll-off: Bays can be loaded onto transport ships
IRB Emplacement Methods:
- Sequential Build: Build from one bank to the other, bay by bay
- Bay-to-Bay Build: Pre-connect bays on shore, launch as sections
- Boat-Assisted: Use Bridge Erection Boats (BEB) to position bays
- Towed Emplacement: Tow bays into position using BEBs
- Stream Launch: Launch from up-current and drift into position
IRB Construction Sequence:
- Site reconnaissance and marking (near shore, far shore, centerline)
- Position and secure shore anchoring system
- Position Bridge Erection Boats (if used)
- Launch first ramp bay on near shore
- Connect interior bays working toward far shore
- Use BEBs to position and connect bays in the stream
- Connect final ramp bay on far shore
- Install and tension anchoring system
- Conduct bridge inspection and proof load
- Open to traffic with traffic control measures
Bridge Erection Boats (BEB):
- BEB M30: 30-foot aluminum-hull boat, twin diesel engines
- Capability: Push, pull, and position ribbon bridge bays
- Crew: 3-4 soldiers (boat operator, engineer, deckhands)
- Navigation: Day/night capability with GPS and radar
- Deployment: Can launch from C-130 or drive on/off ships
Traffic Control on Ribbon Bridges:
- Post traffic control points at both ends
- Maintain 50-meter spacing between vehicles
- Maximum speed: 15 mph (reduced for heavy loads or adverse conditions)
- Stagger heavy vehicles across both lanes (center loading)
- Single-lane operation may be required for MLC 96+ loads
- Stop all traffic for emergency conditions
- Record all crossings in bridge log
IRB as Raft:
Ribbon bridge bays can be configured as rafts for transporting vehicles:
- 4-Bay Raft: Two interior bays plus two ramp bays, carries MLC 80
- 6-Bay Raft: Four interior bays plus two ramp bays, carries MLC 96
- Propulsion: Powered by BEBs attached to sides
- Use: When bridge emplacement is impractical or for retrograde operations
Module 6
Rafting Operations
Rafting operations transport vehicles and equipment across water gaps using floating platforms when bridge construction is unnecessary, impractical, or when conducting retrograde operations. Rafts provide tactical flexibility and reduced signature compared to permanent bridges.
Types of Military Rafts:
- Assault Rafts: Small rubber boats for infantry and light equipment (CRRC, LARC-V)
- M4T6 Raft: Configured from M4T6 float bridge components
- Ribbon Bridge Raft: Configured from IRB interior and ramp bays
- Erection Boats as Rafts: BEBs can transport limited cargo
Rafting Advantages:
- Faster emplacement than fixed bridges
- Reduced materials and equipment required
- Lower signature (can be concealed between crossings)
- Mobile — can relocate as tactical situation changes
- Effective for retrograde operations
- Can operate in currents that prohibit bridges
Rafting Disadvantages:
- Lower traffic capacity than bridges
- Requires continuous operation of watercraft
- Vulnerable to weather and water conditions
- Limited to equipment that fits on raft
- Requires more crew for continuous operation
- Slower crossing rate than bridges
M4T6 Raft Configuration:
- 4-Bay Raft: Two interior bays plus two ramp bays
- Capacity: MLC 16 normal, MLC 24 with supplemental flotation
- Dimensions: Approximately 18' x 36' deck area
- Propulsion: Outboard motors or push boats
- Crew: 4-6 soldiers for operation
Ribbon Bridge Raft Configuration:
- 4-Bay Raft: Two interior bays plus two ramp bays
- Capacity: MLC 80 (one M1 Abrams tank)
- Dimensions: 22' x 66' deck area
- Propulsion: Two BEBs (one each side)
- Crew: 8-10 soldiers (raft crew plus boat crews)
- Crossing Time: 2-4 minutes depending on river width
Raft Site Organization:
- Loading Area: Firm ground for vehicle loading, masked from enemy
- Holding Area: Vehicles staged in priority order
- Mooring Points: Secure points for rafting during loading/unloading
- Approach Lane: Clearly marked path to loading point
- Service Area: Maintenance and equipment storage
Rafting Operations Sequence:
- Conduct reconnaissance and site preparation
- Position mooring lines and anchors
- Assemble raft components at loading area
- Launch raft and position at loading dock
- Secure raft to mooring points
- Load vehicle under direction of raft commander
- Verify load security and weight distribution
- Cast off mooring lines and begin crossing
- Maneuver to unloading dock on far shore
- Secure raft and discharge vehicle
- Return for next load or secure as directed
Rafting Safety Procedures:
- All personnel wear life preservers
- Vehicle engines off during water crossing
- Driver remains in vehicle, all others on deck
- Guide lines/cables available for emergency
- Establish emergency procedures for raft breakaway
- Monitor weather and water conditions continuously
- Post safety swimmers in the water (if conditions permit)
- Maintain radio contact with both shore control points
Raft Loading Procedures:
- Approach raft squarely along centerline
- Guide driver using standardized hand signals
- Position heaviest vehicles in center of raft
- Distribute load evenly side-to-side
- Secure vehicle with tiedowns if required
- Verify adequate freeboard before casting off
- Maximum one heavy vehicle per standard raft
Tactical Considerations:
- Conduct rafting operations at night when possible
- Use smoke and deception to mask raft sites
- Establish security on both banks
- Prepare alternate raft sites for redundancy
- Plan for equipment recovery if raft disabled
- Coordinate with maneuver units for traffic control
- Prepare to destroy equipment to prevent capture