Military Bridging

Origins

Mandrocles of Samos designed and constructed a bridge of boats across the Bosphorous in 493BC. At some 3,000 ft this represented a considerable achievement and enabled Darius and his army to cross from Asia into Europe and invade Macedonia. Mandrocles must have a claim to being one of the very first bridge engineers.

The essence of military bridging is the capacity to provide a fixed or floating structure across a wet or dry gap, frequently in the face of the enemy, such structures being prefabricated, portable and easy to assemble.The Bailey Bridge developed at the start of Second World War (1939-1945) is probably the most well known example. However, in the best traditions of the Corps of Royal Engineers, its officers have been at the forefront of military bridging design since their foundation. Indeed prior to the formation of the Corps in 1716, the Ordnance Train of 1692 included wagon carried pontoons for the Flanders campaign (1692-97).

19th Century Military Bridging (1800-99) - the Pontoons

The first regular bridging train was formed in 1812 and was part of the army in the Peninsula in April 1813. Wellington, ever conscious of logistics, took a great deal of interest in it. The tin pontoons were open and prone to flooding in heavy water. To overcome this Colonel James Colleton designed a cylindrical shaped closed pontoon with conical ends in 1814. At about the same time Sir William Congreve (of rocket fame) produced the Congreve Trough. This was probably the first 'dry' bridge and consisted of 2 U shaped troughs 14 ft long which could be laid across a stream or laid across a boat to form a rudimentary ferry.

Development of pontoons continued apace, Major Blanshard produced a cylindrical design with hemispherical ends in 1836 (referred to as the Blanshard Pontoon - see illustration 2b), an improved version was later designed by Admiral Caffin but quickly superseded.

This pontoon was referred to as the Mark II - see illustration 4a and 4c, in succession, it is suggested, to the Blood pontoon. It could be formed as a light infantry bridge using bow and stern sections separately - see illustration 4b. A heavy bridge could be created by coupling two bows with a stern between them in a tripartite section. Finally it could operate as a raft.

Illustration 4b Mark II pontoon - showing the stern and bow clipped together

Early 20th Century Military Bridging (1900's - 1920)

Illustration 5 - Section of a trestle bridge built over the river Tugela, Natal during the Zulu War in 1879 - the trestles can be clearly seen supporting the deck of the bridge.
Photograph taken by a RE Photographer 1879

The trestles provided support between the bank and the first pontoon and were extensively used during the British colonial wars of the mid to late 19th century, particularly in South Africa - see illustration 5.

An improved version was officially identified as the Mark IV Trestle and widely used in the First World War (1914-1918).

The Inglis heavy pontoon bridge was developed later, this had a square section through which traffic passed. The Type A stock span bridge - see illustration 6, was superseded by the Hopkins 120 ft span bridge (Captain Hopkins was a former bridge designer with the Great Western Railway), this was a through type bridge as well - see illustration 7. Constructed using prefabricated steel sections fixed with nuts and bolts it was not suitable for front line use.

The use of tanks on the battlefield saw the emergence of assault bridging. Large fascines were initially used and indeed are still in use today. Tank towed and subsequently mounted devices were developed and will be the subject of a separate article.

Extreme bravery was the order of the day in constructing infantry footbridges as part of an assault. Three Victoria Crosses were awarded in the period leading up to the Armistice; posthumously to Cpl James McPhie and also to Maj AHS Waters DSO MC RE and Spr A Archibald. Earlier in the war Capt T Wright RE, Capt WH Johnson RE and Maj G de CE Findlay MC* RE were also awarded VCs.

Mid-20th Century Military Bridging (1920's - 1945)

At the very end of the war a permanent home was established at Christchurch, Dorset for all things bridging. It was intended to form three RE Tank Bridging Battalions but plans changed as the war ended and the Experimental Bridging Company (later the Experimental Bridging Establishment: EBE) was formed from one of these Battalions under the command of Major G le Q Martel DSO MC RE who went on to play a signal role in military bridging reaching the rank of Lieutenant-General. The pace of development slackened in the inter war period and equipment developed included amongst others the Canal Lock Bridge, the Inglis Assault Bridge, the Large Box Girder Bridgeand later the Small Box Girder Bridge, the Inglis Heavy Floating Bridge, the Mark IV pontoon, the Mark V trestle, the Folding Boat Equipment - see illustration 10, and the Christchurch Crib. This was a skeleton steel double cube measuring 6' x 3' x 3' used to make temporary bridge piers. Inglis continued to play a role in the development of bridging but was based at the University of Cambridge.

Donald Bailey joined the EBE in 1928 as a civilian designer. It is suggested that the idea of the Bailey Bridge - see illustration 9a, 9b, 9c, was sketched out on the back of an envelope in 1940 as Donald Bailey and others from the EBE returned from the loading trial of a new Inglis Bridge prototype in Cambridge. The EBE's requirement was for an easily manufactured steel bridge whose basic components would each weigh no more than a 6 man lift (600lbs), fit into a 3 ton GS lorry. It had to be sufficiently flexible to be used over a wide range of gaps, with various loads and with pontoons. Bailey drew together the various threads of past developments and proposed a prefabricated K braced panel with male/female couplings and panel pins. Each panel was about 10 ft x 5 ft and had 18' cross girders. The through section was almost 13 ft with a 10 ft 9" roadway. The cross girders extended outside the panels and were used to support walkways. Panels could be added in parallel to form double and triple trusses. Panels could also be laid in layers up to 3 high. A 150 ft triple-triple bridge could carry a Churchill tank on its transporter (about 70 tons).

Military Bridging in the Post-WW2 period (1945 onwards)

In 1946 EBE became part of MEXE (the Military Engineering Experimental Establishment) and its work was directed towards the use of aluminium alloys and the development of bridges with greater capacity and load width to take account of the development of larger and heavier vehicles.

The Light Assault Floating Bridge (LAFB) was the first product. Consisting of a bipartite pier with integrated roadway and panel 2 sections could be carried on a 3 ton vehicle and a further 2 sections on the towed launching trailer. It had an articulated landing bay to cope with changes in river height. It could also be used to form a Light Assault Raft (LAR) - see illustration 11, with a Class 12 or Class 30 load capacity (approximating to a 12 and 30 ton load respectively).

The Heavy Assault Floating Bridge (HAFB) - see illustration 14, followed. This pontoons consisted of 3 sections, a centre and two bows. The girder panels were of made of aluminium, a first in this type of bridging. The centre section was carried on a 10 ton vehicle with the two bow sections being carried on a trailer which was used to launch the complete section. Class 80 capacity for tracked vehicles and Class 100 for wheeled vehicles.

Design of the Heavy Ferry (Class 80) - see illustration 12, began in 1947 with troop trials commencing in 1955. Coming into service in 1957 it consisted of 4 main pontoons each with a ramp, 4 propulsion pontoons and 4 buoyancy pontoons. A system of water jet propulsion was used, water being drawn into the axial flow pump and forced out through guide vanes which provided the directional force. The ferry could be built in an hour and was carried on 6 trucks 4 of which had special trailers. The new dry bridge was the Heavy Girder Bridge (HGB) which was a scaled up version of the Bailey Bridge with a maximum Class 100 load. All of these post war bridges needed a crane to assist in their assembly although the HGB could be built without one. Variants of this bridge were developed together with a new 4 ft x 2 ft x 2 ft bridging crib.

The development of the Class 16 Airportable Bridge which began in the early 1960s saw a step change in construction using alloy materials (aluminium-zinc-magnesium). It was of box construction with internal stiffening and a 50 ft clear span. The top surface of the boxes formed the deck and the end sections were ramped. A floating version with pneumatic floats using standard outboard motors for propulsion was produced as well. There was also a requirement for an amphibious bridge which was initially met by using the French invented and German developed eponymously named Gillois Bridge Unit. This was quickly succeeded by the superior German M2 rig now superseded by the M3 rig. These were completely self contained and powered and could be linked to form ferries and bridges. There is an example at the Museum.

The early 1970s saw the introduction of the Medium Girder Bridge (MGB) - see illustration 13, into service. This innovative bridge of alloy construction was hailed by many as the real successor to the Bailey Bridge. It was lighter in weight, easier to transport & handle and much quicker to build than both the Bailey and HGB. Like the Airportable Bridge it consisted of box sections with ramp ends, with the addition of deck units and bankseat beams. Load capacity could be increased using a reinforcement set to create an under storey. Other developments included a multi-span set and a floating version. The MGB remains in service. The Bailey Bridge has been exploited commercially and a whole range of variants have been developed in steel and alloys.

One More River to Cross Joiner J (Pen and Sword Books, Barnsley)

Follow the Sapper. Napier G (Institution of Royal Engineers, Chatham, 2005)

Related links

Corps History Part 14 - The Corps and the First World War

Corps History Part 16 - The Corps and the Second World War

Article - Assault Bridging and Equipment

Article - Blood's Pontoon

Biography of Charles Pasley