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The latest in tactical bridges: obstacle-crossing for today's mobility forces.

The Latest in Tactical Bridges

Obstacle-Crossing for Today's Mobility Forces

Natural and man-made obstacles are a major element in any plans for the movement of ground forces. Nowhere are they more important than on the battle-field and the approaches to it, both for the defender and for the attacker.

Even quite narrow tank ditches or steep-sided water obstacles can pose formidable barriers to armoured formations. They need be no wider than 24 metres to halt a tank unit dead in its tracks. If they are covered by enemy fire, they are usually best avoided.

There are occasions, however, when they have to be crossed at all costs, either to achieve surprise, or to maintain the momentum of an operation. In such cases, the obstacle must be crossed as rapidly as possible, using either bridges or quickly assembled ferries with sufficient load capacity to carry the heaviest fully-laden vehicle in the formation.

Usually, this is a battle tank. Today's behemoths weigh up to 62 000 kg (the British Challenger), with the Israeli Merkava and versions of the American M1A1 Abrams already fitted with Depleted Uranium armour approaching this figure. For comparison, the German Lepoard 2 weighs in at around 55 000 kg combat-loaded, and the French AMX30B2 at a mere 36 000 kg (though the new Leclerc will be very much heavier).

This article looks at some of the most recent tactical bridging and ferry equipment developed to handle such loads in the battle area.

US Armoured Vehicle-Launched Bridge Competition

The largest western inventory of Armoured Vehicle-Launched Bridges (AVLBs) is held by the US Army, which has 892 scissors bridges mounted on M48 and M60 tank chassis. Since the existing American AVLBs have a maximum load of 60 US tons, or 54 400 kg (Military Load Classification/MLC 60) none of them are able to carry even the lightest variant of the M1 Abrams without exceeding their normally allowable load limit.

Combat-loaded, the basic M1 weighs 54 540 kg. With several thousand Abrams already delivered, and a new AVLB to carry them yet to be selected, it is to be hoped that the latest American battle tanks do not have to be deployed in anger for a few more years.

The US Army has, in fact, been funding an AVLB development programme by BMY, with Israel Military Industries as major subcontractor, since 1983. This calls for a new MLC 70 (63 500 kg) AVLB known as the Heavy Assault bridge, or HAB, to be mounted on an M1 chassis. Until recently the three-section, double-fold HAB was supposed to be 32 metres in length, the bridge weighing only 12 500 kg. To achieve this light weight, the contractors used composites for the bottom chords, and maraging steel in parts of the main structure. In BMY prototype testing, the composites and the maraging steel cracked under the stresses.

The Army has now revised the HAB length specification downwards to 26 metres, having recognized that this is sufficient to cover the maximum 24- metre dry and wet gaps which account for 90% of those found in Europe, and 85% of such gaps in the Middle East. This means that BMY no longer has to use composites or maraging steel, and can reduce the number of bridge hydraulics units from 12 to eight, while staying within the Army's weight limit for the bridge.

BMY is therefore redesigning its HAB under a modified contract signed in 1989. The company has already built a second-generation prototype with new end ramps and centre section. This, however, will now have to compete for the eventual production contract against the 26-metre German Leguan.

The horizontally launched MLC 60 Leguan has not so far been adopted by the German Army, although it has been produced by MAN GHH for the Norwegians, launched from an 8 X 8 wheeled truck. General Dynamics Land Systems was awarded a $ 12.46 million US Army contract in April this year for two prototypes of a redesigned Class 70 version, to be mounted on M1 tank chassis.

GDLS is acting as prime contractor and systems integrator, with MAN producing the new Leguan bridge units. They are to be delivered to the US Army by end of October 1992, for side-by-side trials against the redesigned HAB from BMY.

The US Marine Corps, for its part, is to abandon its independent effort to procure a 24-metre Class 70 Trailer-Launched Bridge, or TLB, from IMI (prime contractor, responsible for the bridge) and BMY. While retaining BMY's specially designed, tilt-frame trailer/launcher system, which is towed or pushed by an M1 or wheeled LAV, the USMC will adopt the US Army's choice between the Class 70 Leguan or the 26-metre HAB to mount on the trailer.

BMY Heavy Assault Bridge and Trailer-Launched Bridge

Using an M1 or M60 tank chassis with the turret removed, the hydraulically powered, forward tilting launch frame for BMY's HAB is attached to the turret ring. The double-fold bridge is mounted on top of the frame. When the latter is tilted forward to touch the ground on the near bank, the three bridge sections unfold vertically, then horizontally under the power of four hydraulic actuators at each of the two folds.

The vehicle's two-man crew can conduct the complete operation, without leaving the tank, in less than five minutes, using the joystick on the vehicle's control box. The bridge can be subsequently retrieved in less than 10 minutes.

The TLB uses a similar technique, but with the power for the launch hydraulics being provided from two 34 hp diesel engines on the trailer/launcher, rather than in the towing tank. As with the HAB, the TLB can be operated from inside the tank. Alternatively, the bridge can be laid from the trailer. This is fitted with four wheels at its rear end and two powerful hydraulic arms to tilt the launch frame. The diesel engines are positioned near to the towing eye. The trailer weighs 7 900 kg. Laying and retrieval times are the same as for the HAB.

MAN's Leguan

With development of the MLC 70 version of the Leguan as an AVLB having only just started, this description is based on the truck-mounted system being produced for the Norwegian Army. The latter placed an order in 1987 for 14 bridgelayers and 14 extra bridges, with an option for a further 12 of each to be used as ferry variants. The first units are already in service.

The vehicle is fitted with a horizontal launch frame on which the two equal-length bridge sections are mounted one on top of each other. The frame slides rearward along the length of the vehicle and contains all the bridgelaying equipment. Each bridge section consists of an identical (and interchangeable) pair of wheel-tread girders 13 metres long. These weigh 2 500 kg per girder.

For laying, the vehicle reverses to within 7.5 metres of the near bank. The upper bridge half is then raised at its front by means of a supporting arm, and the lower bridge half slid out from underneath it, guided by a roller at the rear end of the top bridge half. Once the lower bridge half has been extended horizontally, the top half is lowered 10% and the two halves are automatically coupled, with their centre of gravity over the vehicle's rear axle. The frame is then slid rearward beneath the protruding bridge half, and its outer extemity is supported on jacks at the near bank of the river.

At this point, the complete bridge is slid rearward over the frame by means of a laying arm, until its tip reaches the far bank. This removes the load from the rollers, and the laying arm is withdrawn to lower the near end of the bridge onto the near bank. The supporting jacks are next retracted, and the sliding frame is withdrawn into place on top of the vehicle.

The laying operation takes eight minutes. Recovery of the bridge is done in reverse order, from either bank.

British AVLB Developments

The British Army's current Chieftain armoured bridgelayers are intended to be replaced by Chieftain-based Close Support Bridgelayers (CSBs). Those will be able to carry three new types of Class 70 bridge, each of a different length and capable of carrying Challenger main battle tanks without exceeding their normally permissible load-carrying limits. Due to the limited number of Challengers and their successors, it appears that no extra Challenger chassis will be made available for the CSB role.

The three new bridges are the 26-metre, folding scissors-type No. 10 bridge; the 16-metre, non-folding No. 11; and the 13.5-metre, non-folding No. 12. Two No. 12 bridges will be carried on a single CSB chassis.

They will form part of the Bridging for the 1990s (BR90) family, for which initial development was carried out by the Royal Armament Research & Development Establishment (RARDE). In July 1987 NEI Thompson was awarded a 30 million [pounds] contract for further design and development of the BR 90 family, with design acceptance scheduled for 1991. The contract also includes production options potentially worth a further 70 million [pounds] to the company.

The designs are expected to make significant use of carbon fibre-based special materials, and a number of components have already been tested.

EWK Amphibious Bridging/Ferry Systems

In West Germany, water obstacles are encountered, on average, every two to three km when moving in an East-West/West-East direction, and every five to six km when moving North-South/South-North.

When the 62-tonne Challenger was introduced into the British Army of the Rhine, therefore, the Class 60 German M2B amphibious bridging and ferry system already in service with the German and British armies was upgraded to Class 70 for the British. The M2 is produced by Eisenwerke Kaiserslautern Goppner GmbH (EWK) and was developed with Klockner-Humboldt-Deutz (KHD).

Designated M2D, the modified M2 consist of three 4 X 4 wheeled amphibious vehicles with hinged buoyancy tanks. The latter are carried on top of the vehicles in travel configuration, and are swung down on each side for operation. An on-board light alloy crane then places the ramps and roadway decking in position across the vehicle. For each of the three vehicles, the decking is 7.6 metres long and 5.5 metres wide, prior to their being coupled together. To accommodate the extra Class 70 load, engine-inflatable bags have been added at the front and rear ends, and on the centreline.

The four-man vehicle has two engines. For amphibious operation, with the wheels retracted, one engine drives a 650 mm steering propeller, while the other drives two 600 mm side propellers. One of these can also be steered.

EWK has now developed a redesigned M3, which is undergoing trials. This carries slightly longer ramp/roadway sections (8.3 metres), and only two vehicles, rather than three, are required to carry a Class 70 ferry load. Also, only eight M3 vehicles are required to build a 100-metre floating bridge, as against 12 M2s.

In addition to the slightly increased length, the hull shape has been redesigned, and the propellers replaced with two recessed waterjets driven from a new 265 kW KHD super-charged engine. Total vehicle weight is 25.3 tonnes.

Engin de Franchissement de l'Avant

The latest item of bridging equipment to be ordered for the French Army is the Engin de Franchissement de l'Avant (EFA), developed and produced by Chaudronnerie et Forges d'Alsace (CEFA). CEFA is producing the EFA under an order for 70 units, to replace the Gillois ferry.

Primarily designed as an autonomous ferry, the EFA can also be used as a bridge, either on its own for obstacles 20-30 metres wide, or by joining several units together for wider rivers. One EFA can carry a single MLC 70 load, or a total of 90 tonnes if several vehicles are evenly distributed along its load-carrying platform.

Normal crew is four men, but it can be operated by two men in emergencies. The 4 X 4 wheels are all steered and tyre pressures can be adjusted while operating. In water, it is steered and propelled by a swivelling pump jet unit at either end of the main hull. Power is provided by a 730 hp Baudouin 12F120SR Diesel engine.

The EFA weighs a total of 40 tonnes, its construction being of aluminium alloy. The main hull is fitted with inflatable air bags along each side. On top of the hull are mounted two scissors-type, double folding ramp sections, one at each end, with inflatable flotation bags incorporated under each ramp. The ramp sections unfold in the vertical plane under hydraulic power, to provide an overall ferry length of 34.66 metres. When used as a bridge, the outer halves of each ramp section rest on the banks, giving a bridge length of 23.5 metres. Usable width of the trackway is 3.6 metres with a 0.4 metre footbridge along the sides of the main hull and inner ramp sections.

Maximum road speed of the EFA is 60 km/h, and it achieves 12 km/h in water when fully loaded.

MAN Folding Float Bridge

Based on German Army experience with its US-built (ConDiesel) Ribbon Bridges, derived from the Soviet PMP bridge system, MAN GHH has developed the MLC 70/80 Folding Float Bridge 2000, or FSB 2000. This is now in competition for US Army procurement as an Improved Ribbon Bridge against an upgraded Ribbon Bridge designed by BMY.

The Improved Ribbon Bridge specification calls for positive flotation, flotation stability against water speeds of 3 m/sec, longer ramp bays to accommodate bank heights of up to 2 metres and a 10-tonne launch truck in place of the current 5-tonne vehicle.

Competitive evaluation is scheduled to begin in 1991. In the US the FSB 2000 prime contractor would be General Dynamics Land Systems.

The FSB 2000 can operate with MLC 70 loads (or, in exceptional cases, MLC 80) in water currents of up to 3.5 m/sec. Like the Ribbon Bridge, it can be used to build either ferries (propelled by pontoon boats) or floating bridges.

Also like the Ribbon Bridge, its individual inner and ramp sections are each carried folded in a W-configuration on the back of a cross-country launcher truck. In operation, the 7-tonne capacity truck backs down to the river bank, the bridge section slides into the water and then automatically unfolds.

The aluminium alloy FSB 2000 has a 30 [degrees] angled bow at each end. A single-vehicle MLC 70 ferry consists of two ramp sections and two centre sections, i.e. four truck-loads. Trackway width is 4.1 metres, with a 2.2-metre wide footbridge on either side. The ramp sections can be adjusted for bank heights of up to 2.2 metres.

Israeli Two-Tank Ferry Raft

Israel Military Industries' 21-metre-long Two-Tank Ferry Raft (2TFR) has now entered service with the Israeli Army. It is towed on an eight-wheeled bogey to the battle area by heavy truck or semi-trailer, and then hitched to one of the two tanks that will use it. The tank then tows it to the water obstacle and launches it. The bogey is then dropped and the tow-boom automatically uncoupled from the tank.

The 2TFR consist of a load platform 5 metres wide, with two 1.6 metre wide side floats that fold downwards from their stowed position on top of it. A hinged loading ramp 7.5 metres long and 5 metres wide is fitted at each end of the load platform. The side floats and load platform are filled with rigid polyurethane foam to ensure buoyancy in case of battle damage.

For propelling in the water, two power units are fitted. These are controlled from either one of two control housings. Each power unit drives a separate propeller or hydro-jet engine that is rotatable through 270 [degrees] for steering. The propeller shafts can be raised or lowered for varying water depths.

PHOTO : EWK's revised M3 amphibious system based on the M2 developed with KHD. An MLC 70 ferry

PHOTO : load is carried on two trucks.

PHOTO : The BMY Heavy Assault Bridge (HAB) fully deployed from its M1 chassis. Originally 32

PHOTO : metres long, its length is being reduced to 26 metres.

PHOTO : The USMC is giving up the idea of procuring a 24-metre TLB (Trailer-Launched Bridge),

PHOTO : shown here, and will adopt either the Leguan MLC70 or the 26-metre HAB.

PHOTO : The horizontally launched MLC60 Leguan from MAN GHH has not so far been adopted by the

PHOTO : Bundeswehr although the Norwegians have procured it.

PHOTO : Dry gap-crossing illustrated by the Leguan. The bridge is launched from an 8 X 8 wheeled

PHOTO : truck.

PHOTO : Sketch of Automotive Bridge Launching Equipment (ABLE) from NEI Thompson Ltd. capable of

PHOTO : launching a 32-metre bridge in under 30 minutes.

PHOTO : Primarily designed as a ferry, the EFA (Engin de Franchissement de l'Avant) from CEFA, can

PHOTO : also be used as a bridge. 70 are being produced for the French Army.

PHOTO : The EFA shown in its road configuration. Built of aluminium alloy, the main hull is fitted

PHOTO : with inflatable bags on either side for use as a ferry.

PHOTO : Competing with an upgraded BMY Ribbon Bridge for US Army procurement is MAN GHH's MLC

PHOTO : 70/80 Folding Float Bridge/FSB 2000, shown here at launch.
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Title Annotation:includes related articles
Author:Furlong, Robert D.M.
Publication:Armada International
Date:Aug 1, 1990
Previous Article:A look at surface-to-air missilery worldwide: covering both shipborne and land-based systems.
Next Article:British Army equipment for the nineties.

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