UK Military Bridging – Equipment (Pre WWII Equipment Bridging)

The title for this post should really be ‘everything up to the Bailey Bridge’ because equipment bridging took a leap forward with the Bailey that made all before it more or less redundant although as I will show, the Bailey would not have been possible without the innovations introduced in the bridges described below. Most of the designs here saw service during WWII but were designed prior to it, hence inclusion.

Inglis and Hopkins Bridges

The earliest forms of equipment bridging were based on pontoons and trestles which I have covered in a previous post on floating equipment. The first British equipment bridge was called the Inglis Portable Military Bridge (Light Type) introduced during WWI although a number of Stock Spans were introduced earlier but these were used in construction bridging rather than as a self-contained portable bridge.

Sir Charles Edward Inglis gained a fellowship of the University of Cambridge in 1901 and during his work with the University Officers Training Corps produced a design for a single file infantry bridge. He was commissioned into the Royal Engineers in 1914 and between 1916 and 1918 he was placed in charge of the department responsible for military bridges within the Corps. This was to start a long period of fruitful association with the Royal Engineers.

The first Inglis bridge was often called the Inglis Pyramid Bridge because of its unique construction but it was effective, easily transported and required little specialist training. The construction members were 8ft long steel tubes connected by specially designed fittings, not unlike modern scaffolding. The W configuration of girders was called a Warren Truss, after a captain of Royal Engineers of the same name.

Although the transoms were heavy at 198 pounds (90 kilograms) the tension tubes were very light and this, coupled with the simple construction technique, enabled a 108 foot long bridge to be completed in less than 15 minutes. Originally intended only for infantry and able to carry single file infantry over a 96 foot span it was able to carry 3 ton vehicles by keeping the centres less than 16 feet apart, 10 sets were ordered for use in France. The next evolution of the Inglis pyramid bridge used longer tubes and heavier construction to support vehicles over longer spans.

The tubes were fabricated at the Round Oak steelworks in Brierley Hill, West Midlands, which is now the site of the Merry Hill Shopping Centre.

Taking the tubular construction system, Charles Inglis created an entirely new design, the Inglis Bridge Mark I, instead of pyramidal design which was impractical for vehicles, its sides were vertical and supported by cross beams. The Mark I was able to support Class A (equivalent to MLC40) loads over a clear span of 96 feet. The junction boxes were of cast steel construction and this allowed rapid construction. The Mark I was used extensively during the final assault in 1918 after being introduced in 1917 and was often called the Inglis Rectangular Type.

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From Canada in the Great War;

A number of standard-span portable bridges, varying in span from sixteen to eighty-five feet, were stored at the base depots. These bridges consisted of loose members and were bolted with machine-turned bolts. They were, however, very cumbersome, and this rendered their erection slow. The weight was another disadvantage, e.g. the eighty-five-foot span was a single-way bridge and weighed sixty-three tons.

Fortunately a new bridge, called the “Inglis Portable Military Bridge, Rectangular Type,” had been invented by Captain Inglis, R.E., and was adopted by the British Army. This bridge was the Warren girder type and was composed of a number of identical bays, each twelve feet long, twelve feet high, and twelve feet wide. It was designed to carry a dead load of eighty-four tons distributed over a clear span of eighty-four feet. Each part could be easily manhandled and the span could vary in multiples of twelve feet, e.g. sixty feet, seventy-two feet, eighty four feet, ninety- six feet, and one hundred and eight feet, to suit the gap. The bridge was built on blocks in skeleton form with a counterbalance arm and jacked up on to a two-wheeled trolley. It was then pushed over the gap, the counterbalance removed, then jacked down on the abutment, and the decking laid. On the 28th of September, 1918, a bridge of this type was erected complete over the Canal du Nord at Marquion in twelve and a half hours actual working time under severe shell-fire. A party of approximately two hundred sappers was employed on the construction of the bridge with the necessary approaches and abutments. The span was one hundred and eight feet clear and the safe distributed load fifty-one tons.

At the end of the war the Mark II Inglis was introduced with greater load carrying capacity, able to support the 35 ton Mark V** tank, and all the tubular sections of the same length.

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A cheaper alternative was the Hopkins Bridge that used conventional steel girder forms bolted together but this was much slower to construct than the Inglis. The Hopkins Bridge was used to cross the Canal du Nord at Havringcourt, I covered this in an earlier posts, click here

After the Great War the Inglis Mk II continued to be used and developed into assault and floating bridges. The Inglis Assault Bridge was a 135 foot long span with a pair of idler tracks. The concept called for the Royal Engineers Tank to use its jib to push the assembled bridge over the gap. In less than a minute a 70 foot gap could be bridged without exposing any personnel to fire, the first true assault bridge to use a bridge of substantial length, over the standard 30 foot assault bridges of the time.

With the demise of the RE Tank (a modified Mark V** shown above) the Inglis Mk II Assault Bridge was not brought into service but the experience was to be used later for a tank launched Mark III (shown below) and a couple of variants of a launched Bailey Bridge.

This new design of assault bridge was also not bought into service because of the introduction of the Mobile Bailey but problems encountered with maintaining stability whilst being transported and launched were incorporated into the Bailey design.

The Inglis Mark II was out of service by the outbreak of WWII but a Mark III design was proposed by Charles Inglis and this is of particular note because of the use of doubling or tripling the unit construction members to increase the class. The Mark III used the same basic design as its predecessors, tubular construction and W shaped Warren Girders connected using specially designed couplers.

The bay length was the same as the Mk I at 12 feet but as a result of this geometry, overhead bracing was not possible. After some controversy regarding the testing method used an order for one hundred 120 foot sets was placed but was soon eclipsed by the Bailey Bridge.

There are two remaining Inglis Bridges in the UK

The first is a Mark II, in Monmouth, over the River Monnow. Recently closed to vehicle traffic it was maintained by the MoD because it marked the entrance to the headquarters of the Royal Monmouthsire Royal Engineers (Militia) at Vauxhall Field. It was built in 1931 to replace an old wooden bridge.

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There are also a couple of Hopkins bridges also over the Basingstoke Canal in Aldershot, one between the Army Cricket Ground and Army Golf Club.

It is a shame that such important military industrial heritage is not better preserved.

Callender-Hamilton Bridge

In the immediate pre-war period most of bridging designs came out of Christchurch but the Callender-Hamilton was an exception. Archibald Milne Hamilton was a New Zealand born civil engineer responsible amongst many things for a strategically important road through Kurdistan between Northern Iraq and the Iranian border, described in his book, here it was a incredible feat of civil engineering.

During the construction of the road many bridges were needed and most of them were built with surplus British military bridges such as the Stock Spans and Hopkins Bridges. Hamilton came up with the idea of a set of standard parts that could be fitted together to form different lengths and loan carrying capacities. The strength was varied by bolting together multiple angle sections, much like the concept for the later Inglis and Bailey bridges.

The concept was demonstrated to the Royal Engineers and Signals Board.

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The Callender-Hamilton Bridge was genuinely innovative and manufactured in two variants. Type A used 5 feet bays and 5 feet trusses with the Type using 10 feet trusses and bays. The Type A was mainly used by local authorities to repair bomb damage and the Type B was adopted by the Army and called the Unit Construction Bridge, this combined single and double trusses to create a 140 foot long bridge that could support tracked vehicles up to 30 tonnes although this was varied as needs dictated.

The CH bridge was not rapidly built but it was very strong and robust, thus, they were used not for assault bridging but as follow on semi-permanent bridges on lines of communication.

Many wartime and post war examples remain in service. The longest lasting temporary bridge in the UK is over the River Eden Langwathby, click here to view and the Walton Bridge over the Thames used a CH type from 1950 to 1983. The Indian Railways make extensive use of CH Bridges and have an excellent guide on their deployment (including a nifty picture of Christchurch Cribs), click here to read. A number have been used on the trans Labrador Railway (click here), for any metallurgists in the house and an interesting advert here.

Painter Brothers are also still in business today as part of the Balfour Beatty Group, manufacturing Callender-Hamilton bridges for use worldwide, click here to visit their website. Modern CH bridges are of course an improved version and can span lengths up to 150 meters long and 3 lanes wide but the fundamental design remains unchanged. Acrow Canada distributes the Painter Brothers CH Bridge in North America.

Large Box Girder Bridge

Another important step on the way to the Bailey Bridge was the Large Box Girder Bridge, the first military equipment bridge in the world to use prefabricated box shaped sections.

Once Major Gifford Martel had taken command of the newly formed Experimental Bridging Establishment his first task was to continue trials with the Canal Lock Assault and Inglis bridges but he also started work on what was to be his most important contribution to military bridging.

He identified that with the Inglis Bridge and Stock Spans a considerable proportion of the weight and build time was taken up with providing the roadway, they lacked adaptability and in the case of the Inglis Bridge, expensive.

He therefore developed an entirely new concept that would use common building blocks to form different length bridges, each section pinned together as necessary depending on the length and load carrying requirement. It was these modularity that would later be developed in the Bailey Bridge.

Launching was normally carried out using gin derricks and shear legs as described in the previous post on construction bridging but cantilevering the bridge across a gap was also carried out. Once to two girders were in place they were adjusted to the correct spacing the decking planks placed across them with ever fifth being oversize to accommodate a footway. Angle iron was pinned in place to form a curb.

Adopted by the Army in 1925 the Large Box Girder Bridge was adaptable and relatively cheap, able to carry loads of up to 40 tonnes, it remained in service until replaced by the Bailey.

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Click here to see an image.

The Mk II was introduced in 1938 with a number of changes; a larger main box unit, a new hornbeam, higher strength steels and new chrome molybdenum pins. The new bridge in 4 girder form could accommodate Class 24 loads at a span of 130 feet.

As can be seen from the image below, Mark II Large Box Girder panels were not small.

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Small Box Girder Bridge

I looked at the role played by the Small Box Girder Bridge when combined with the Churchill tank during D Day and beyond in the previous post on assault bridging but prior to being used in this manner it was also used more conventionally.

The maximum vehicle load at the time apart from tanks was less than 10 tonnes and with the introduction the new medium weight tanks it was thought a bridge that was easier to transport and faster to build than the Large Box Girder bridge would be a valuable addition.

The Small Box Girder bridge was in effect, a scaled down Large Box Girder bridge and after a series of trials and modifications was formally introduced in 1933.  The 8 feet 6 inches fixed width timber decking was laid on two or four girder sections up to 64 feet long.

Launching was completed using a lightweight launching nose that had a small wheel fixed to the end. Construction times were very low, a well trained team could bridge a 60 foot gap in less than 20 minutes. Donald Bailey, who was by now working at the EBE, recommended the use of high tensile strength steel and new welding techniques and it was this that allowed such a light structure to carry the required loads.

Clips from British Pathe show the Small Box Girder Bridge under construction, here, here, here and here

Its ultimate form, the Mark III SBG bridge, was Class 12 at 64 feet in 2 girder configuration and Class 24 at the same span in 4 girder configuration.

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The Small Box Girder bridge was copied and used by many other nations including Germany (where it was called the Kastenrager-Great or K-Gerat) and the United States where it was called the H-20

So we can see that the Inglis, Callender-Hamilton, Large Box Girder and Small Box Girder bridges all contributed ideas and techniques (modular panels, welding, steel selection, launching nose and combining structural members) that would be utilised on the Bailey bridge.