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 takedown 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 below, 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 does 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.

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.

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;

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

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;

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

The Inglis Bridge was without a doubt the best military bridge of the time with short construction times and high carrying capacity but because of its tubular steel construction, was 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
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Mark V. tank leaving a raft of pontoons with Inglis Tubular Frame. IWM
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Rafting a Mark V. Tank over a pontoon raft stiffened with Inglis Tubular Bridge. IWM
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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 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, it was 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 doubled 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 overbuilding. 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.

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.

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

Finally, a single truss Mk III at recently discovered at the former RAF Sandoft

The local branch of the Royal Engineers Association (REA) and the Royal Engineers Museum were enlisted to preserve and transport it to the RE Museum. The Highways Agency and local Water Board gave permission and wheels set in motion to rescue this rare item of UK military heritage.

Images from the removal below

This is great stuff, however, I do wonder if this is actually a single truss MkIII. I have never seen any drawings or images of a MkI with the infantry footbridge and stabilising outriggers, only a MkIII. The MkIII could not have overhead transoms and so to provide additional resistance to buckling, the diagonal bracing was added to the enlarged deck transoms, as seen in the one at Emmerich. As can be seen from images above, there are sections in the MkIII that only had a single truss. Also, given the timeframe, when the bridge here was installed, in the mid-forties, the Mk I would have been long gone, but the MkIII would have been available, and more importantly, surplus to requirements given the introduction of the Bailey Bridge.

I could well be wrong, and the bridge in question might be a mix, certainly, during the war, anything surplus would have used.

Further Information

There are a handful of Inglis Bridge related patents online;

• Improved bridge trestle, abutment, landing stage, pedestal or like framework
• Triangulated framework
• Improvements relating to triangulated frameworks and their application to the construction of bridges and the like
• Bridge Construction
• Improved crane suitable for erecting and launching bridges and similar girder constructions
• Improved junction-box for use in connection with triangulated frameworks
• Improvements relating to triangulated frameworks and their application to the construction of military bridges and the like
• Improvements in or relating to Joints and Joint-boxes for Tubular-members of Military Bridges and the like.
• Improvements in or relating to Military Bridges and the like

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