The Inglis Bridges

When most people think about portable military bridges they tend to assume the Bailey Bridge was the first, but this would be wrong, Charles Edward Inglis designed the first dry gap prefabricated military bridge in service with any Army anywhere in the world. Although a number of Stock Spans were introduced earlier, they were used in construction (non-equipment) bridging rather than as a self-contained portable bridge.

Charles Edward Inglis (pronounced Ingles) was born in July 1875 to Dr Alexander Inglis and Florence Inglis (nee Feeney). After winning a scholarship to Kings College Cambridge, studying both mathematics and engineering he left academia to spend time as a bridge design engineer he re-entered academic life to become the first Fellow in Mechanical Sciences at King’s College in 1908. In the early pre-war period Charles Inglis was involved with the Royal Engineer section of University Officer Training Corps and started the preliminary design work on a portable infantry bridge.

With the outbreak of war he volunteered for service and was commissioned into the Royal Engineers and appointed to an instructor post at the School of Military Engineering in Chatham. By 1916 he was in charge of the Corps bridge design and procurement section, continuing work on a number of different bridge designs.

After the war he returned to Cambridge University as the professor of Mechanism and Applied Mechanics and in 1919, awarded an OBE.

After a long and distinguished academic career he was due to retire in 1940 but the Second World War saw interest in his bridge designs rekindled and he was involved in military bridging for a second time.

Charles Inglis was knighted in 194 and died on the 1^st of April 1952, read his obituary here

The Inglis Pyramid Bridge

The first Inglis bridge stemmed from work carried out in 1913 on an infantry bridge.

His obituary mentions this early period;

He had been an officer in the University O.T.C., and had noticed how on field days the engineering section had to stand about for hours with nothing to do. So he designed a bridge which they could put up and take down in the course of an afternoon. An inspecting officer noticed it, and said, ‘If you’re making anything for the army, keep it simple – no complicated gadgets

Officially called the Inglis Portable Military Bridge – Light Type it was generally known as the Inglis Pyramid Bridge. As can be seen from the diagram belows, the Warren trusses were angled in and secured with a single tubular top chord placed in compression. The bottom tubes were in tension and a number of trusses supported the single gangway.

Although the transoms were heavy at 198 pounds (90 kilograms) each, the tension tubes were very light (similar to scaffold tubes) 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. A two wheel trolley was used to assist in construction with the bridge being initially constructed parallel to the gap. Once complete the bridge was swung over the gap with the construction team providing the cantilever weight.

10 sets were ordered for use in France.

It was also possible to carry 3 ton vehicles by keeping the centres less than 16 feet apart and combining two bridge sets.

The first demonstration in France saw the Army Service Corps span a 108ft gap in 13 minutes using an Inglis Light Type. Soon after, the BEF requested a modified design that could carry first line transport vehicles up to 7 tons over a 96 foot gap.

Inglis responded by designing the Inglis Heavy Type Bridge.

Instead of 8 foot tubes the Heavy Type used 12 foot tubes and could carry loads up to 7 tons over a span of 96 feet. 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. 17 Heavy Type Inglis Bridges were ordered and delivered to France in 1916 although they did not see widespread use because the triangular construction meant tall vehicles could not traffic the bridge.

A further modification was proposed that truncated the pyramid structure although this was not produced.

There is only one original Inglis Pyramid Bridge left anywhere in the world and it is in the UK.

An Inglis Portable Military Bridge (Light Type) with the pyramidal construction is situated in Aldershot, just off Laffan’s Road near Browning Barracks. Laffan of course is familiar to any Sapper in the Hurrah for the CRE song, a former CRE. In WWII, Malta Barracks was on the edge of Laffan’s Road on the edge of Watts Common and was used for Royal Engineer training as well as the nearby Hawley Lake. The bridge itself is between the Claycart and Farnborough Road bridges (see the Google map at this link).

It is used as a pipe support although I am not sure what the pipe carries.

This marvellous and historic piece of the nation’s military engineering heritage sits there alone and largely unknown, although the Basingstoke Canal Society do have some information on it and the Pill Box Study Group have documented a nearby pillbox (funnily enough!)

To commemorate men lost from the area during the First World War, South Ribble Borough Council commissioned DP Studios to recreate an Inglis Heavy Type Bridge for use in their Central Parks area.

A few days earlier saw the unveiling of the continuation of the memorial area. The Inglis bridge erected over the River Lostock (or dandy brook) is based on a World War 1 design. In previous conflicts, rivers were spanned using boats and timber beams lashed together to form pontoons. Although much of the Great War was fought from the trenches, when the order came to advance, speed of movement became the key to success. A new type of bridge was needed. A modular bridge which was light and portable. Charles Inglis had already considered the issue and had a design ready to go. In the field the bridge was used to support front line troops. The sappers were often called upon to build bridges whilst under fire. The rapid deployment of the Inglis Bridge helped to reduce the casualties. As the fighting moved forward the sappers would erect a more permanent structure whereupon the Inglis Bridge would be dismantled and transferred forward to support the next offensive. The new bridge is based on the version developed by Charles Inglis during 1915 and referred to as the ‘Heavy Type. Every effort has been made to recreate the bridge as closely as possible to the original. However, for safety reasons, the following design changes have been introduced; the timber transoms (large members across the base) are replaced with steel, steel decking is installed and safety barriers added. The bridge is fixed and cannot be disassembled.

See it on Google Maps here

The Inglis Bridge Mark I and Mark II

With the emergence of the tank it was clear that the existing stock spans and portable bridges would be unable to carry them, a new bridge was needed. By now responsible for all military bridging in the British Expeditionary Force, Charles Inglis was tasked by the Engineer in Chief to design an improved tubular bridge to carry heavier loads as typified by early tanks.

The resultant design took the tubular construction from the earlier Inglis pyramid bridges but used a more practical design with a lightweight pierced top web. The junction boxes were still cast iron and it used the same tubes as earlier designs. The transom was of similar design to the top web.

Inglis Bridge - Square Type
Inglis Bridge - Square Type Drawing

The Inglis Mark I (or Square Type) was able to traffic Class A loads (17 ton axle load) over gaps up to 96 feet wide using a 12 foot bay.

The image below shows an 84 foot MkI in use at la Motte in France, April 1918.

Canada in the Great War provides an excellent description of the build process;

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.

After arriving in late 1917 it was widely used in the final advance in 1918.

Inglis Bridge Mk I - River Somme
Inglis Bridge Mk I - River Livenza

Chemin Vert Loop Line. Heavy Inglis type bridge carrying Bray-Chuignolles Road over River Somme at Bray. IWM

Bridging Company Royal Engineers constructing bridge over River Livenza alongside which had been destroyed by the Austrians. IWM

Although a big step up in load carrying from earlier designs the unequal tube lengths could cause confusion during night builds and the new heavy tanks were still too heavy for it. By the end of the War the Inglis Bridge Mark II was under trial, essentially a strengthened Mark I with 15 foot bays. A key improvement was a return to identical length tubes. The Mk II (Strengthened Type) could carry a 35 ton Mark V** tank over a 105ft span.

From the same Canadian journal as above;

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.

And here is a picture of them doing just that at the Canal du Nord in 1918

An Inglis Mark II was also used to span the Jordan River in Palestine, this being called the Allenby Bridge

Lord Allenby Bridge - Opening
Lord Allenby Bridge

The Inglis Bridge was without a doubt the best military bridge of the time with short construction times and high carrying capacity but because it’s tubular steel construction, expensive.

As the war entered its final stages it became ever clearer that the rapid bridging of tank obstacles and rivers/canals would be a vital element of armoured warfare and so in October 1918, three Royal Engineer Tank Bridging Battalions were formed, the first Royal Engineers armoured capability and the first in the world. Each battalion was equipped with twelve Inglis Mk II (Strengthened) Bridges and a number of Heavy Pontoons. Each would also have 48 tanks equipped with the 21 foot Canal Lock Bridge.

The Canal Lock Bridge was also designed by Charles Inglis, aided by Major Giffard Le Quesne Martel.

Soon after the Armistice, two of three Tank Bridging Battalions had been disbanded but the remaining one was reformed under Martel to become the Experimental Bridging Company Royal Engineers at Christchurch

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 21 foot Canal Lock assault bridges of the time.

The image below shows an Inglis Mark II Assault Bridge

With the demise of the RE Tank (a modified Mark V** shown below) the Inglis Mk II Assault Bridge was not brought into service but the experience would inform later assault bridge designs. The use of the Inglis Mark I and Mark II in floating bridge arrangements were also trialled in the immediate post war years.

: Mark V** Female tank and Inglis Mk II pontoon bridge Experimental Bridging Establishment, Christchurch, 1918

: Mark V. tank leaving a raft of pontoons with Inglis Tubular Frame. IWM

: Rafting a Mark V. Tank over a pontoon raft stiffened with Inglis Tubular Bridge. IWM

The Imperial War Museum has an online video of Inglis pontoon and assault bridging at Christchurch in 1918, click here to view

After leaving the Army and returning to Cambridge after the war Charles Inglis continued his close association with military bridging, designing the Inglis Heavy Floating Bridge for example. By the early thirties the Inglis Mark I and Mark II were out of service although they continued to be used for training and development and occasional use outside the UK such as the Barra Bridge in the Peshawer District India, in 1930.

From the National Army Museum

The ‘Inglis’ pattern bridge, named after its inventor, Lieutenant later Professor Sir, Charles Inglis, (1875-1952) was constructed across the Bara River by No. 4 Field Company, King George’s Own Bengal Sappers and Miners. The specifications required that it be capable of carrying infantry in fours or 10 ton steam rollers, one at a time. Work began on 29 October 1930 and the bridge was open for traffic on 23 November. Photograph from an album compiled by C G S Clarke, 1st King George’s Own Bengal Sappers and Miners, 1930-1931.

The Inglis MkII was still in service at the outbreak of the Second World War and despite the existence of the Large and Small Box Girder bridges the Inglis was retained because it was so flexible. The Mark II did have one last hurrah as the Inglis Mobile Bridge although after extensive testing, it was not bought fully into service. During this Period Charles Inglis also designed an improved crane system for building his bridges and a trestle for pontoon or floating bridges.

There are still a small number Inglis Mk I and II’s in existence.

An Inglis Mark II bridge is in Monmouth over the River Monnow, built in 1931 to replace an old wooden bridge.

See the bridge on Google Maps here

Recently closed to vehicle traffic it was maintained by the MoD because it marked the entrance to the headquarters of the Royal Monmouthshire Royal Engineers (Militia) at Vauxhall Field. The Royal Commission on the Ancient and Historical Monuments of Wales has a small image gallery for the Inglis Bridge at Monmouth.

The Inglis Mark III Bridge

At the outbreak of WWII the Royal Engineers found themselves, like much of the British Army, without sufficient equipment for modern mobile armoured warfare and a widespread design effort was initiated. Charles Inglis suggested a redesigned Mark II Inglis Bridge. The Mark III Inglis Bridge was very similar to the Mark II but allowed the tubular trusses to be double or tripled up using a redesigned junction box.

With three trusses, the bridge was designed for Class 24 loads. By using multiple trusses the bridge would provide Sappers with the flexibility to avoid over building. Reverting to the 12 bay length of the Mk 1 meant the height of each truss was such that the Mk II top beams and sway bracing would not be possible if in service vehicles were to traffic it.

As it was developed some disagreement between Inglis and the EBE over test methods resulted in a test failure on 23rd January 1941.

An order for one hundred 120 foot sets had already been placed so a quick solution was needed. Overhead bracing was out of the question so the solution proposed and accepted was to add a footwalk bracket to each end of the transom and use diagonal bracing from this to the top of each truss. The image below shows the bracing and footwalk brackets on a single, double and triple truss configuration, and on the left, the launching trolley.

Although the Mk III was an effective design it was still expensive and was soon eclipsed by the Bailey Bridge.

There were a number of Mk III’s still in existence.

Some time ago I received an email from Derek at the RE Museum (another fellow bridge enthusiast) about their efforts to identify a bridge in Emmerich, Germany.

I am a volunteer in the R E Museum, We received an e-mail inquiry from a man who lives in Emmerich, Germany asking for help to identify an Inglis bridge that was still in use over a river called The Wild. I have recently visited the bridge and found out it was built in late 1945, possibly by British Sappers and has now been declared a war monument by the German Government. It is in very good condition and is now restricted to 16 tons

And there it is, over the Die Wild at Spiker Weg is none other than an Inglis Mk III, click here to view on Google Maps.

Inglis Mk III Emmerich - Image 1
Inglis Mk III Emmerich - Image 2

Like Monmouthshire and Basingstoke, Emmerich has a long history of association with the Royal Engineers so it seems fitting for the three types of Inglis Bridge are in each of those locations.

Thanks Derek

A spot of additional Google Fu reveals what looks like another MkIII Inglis but without the additional trusses. This one is in New Zealand at the Simpson Domain camp site erected by the Rangitikei County Council in 1985, details here