The pontoon bridge is probably the oldest form of military bridging equipment, back to the original ‘Bridge of Boats’ I looked at the beginning of the series.
At its simplest form, a pontoon bridge is a collection of shallow draft boats, lashed together across a river or canal, with some form of track or deck lashed to the top.
The water acts as a support so the limitation on load carrying is governed by the total and point buoyancy of the pontoons or boats.
The reality of pontoon bridges is that they haven’t progressed much since then.
Of course materials have improved, techniques for anchoring the pontoons, decking materials and so on have led to improvements in load carrying capacity, the ability to withstand fast currents and speed of deployment but the basic principles remain.
An even older variant of the pontoon bridge is the river ferry, a simple, unpowered flat bottomed boat that is hauled across a wet gap using human, beast or engine power.
A pontoon bridge will in general have a much higher volumetric throughput than a ferry but a pontoon bridge has the distinct advantage of not blocking the river or canal to other vessels. In fast flowing rivers and those with high tidal ranges a pontoon bridge might also suffer without extensive anchoring and constant attention from the bridge builders.
Pontoon bridges and ferries now often share components, for example, the Bailey Pontoon, not surprisingly, used many Bailey bridge parts and the modern Air Portable Ferry bridge can be used either as a bridge, pontoon or ferry.
It is therefore difficult to split the development of pontoon bridges and ferries because they are so inter-related.
These early open boat type pontoons had a number of disadvantages, difficulty in transporting them to site (if not riverborne) and susceptibility to bad weather amongst many. It was in the early 1800’s that a concerted effort was made to improve the design. In 1814 Colonel Sir James Colleton designed a cylindrical pontoon that unfortunately was not a success but it did form the basis for later types.
The first significant development after this was the 1817 Pasley Pontoon, designed by Lt Col Charles Pasley of the Engineer Establishment at Chatham. The Pasley Pontoon differed from the open boat type in a number of key areas. It was enclosed and therefore had greater resistance to swamping, had many lashing points for attaching the bridge deck and perhaps more importantly, was sectional. The bow was pointed and the stern square ended. This allowed the pontoon to be broken down into two for ease of transport and fixed together to form a single float whose ends were both pointed, an important consideration in wet gaps that had tidal flows. The Pasley Pontoon saw many years service but was replaced in 1836 by the Blanshard Pontoon which was cylindrical with parabolic ends. Handles were sunk into the body of the pontoon for handling and lashing with two 24ft long pontoon carried on a single horse drawn wagon.
The trials that would result in the successful entry into service of the Blanshard Pontoon were described in the Army and Navy Chronicle of November 1836, click here to read.
Writing in the Royal United Services Institute Volume 9 in 1865, Lt Col Lovell RE described in some detail the use of pontoons in military bridging.
Click hereto read, this is a really interesting edition that includes some great reading on the use of electricity on military operations, naval tactics, magnetism of ironclad ships and current state of the ‘artillery question’
With one or two modifications the Blanshard Pontoon stayed in service until the late 1870’s when they were replaced with the Blood Pontoon.
Designed by Sir Binden Blood RE (cracking name by the way) the Blood pontoon was interesting because it returned to the concept of the open boat design.
From his memoirs, Four Score Years and Ten, published in 1935.In 1865
I was appointed to one of the Troops of the Royal Engineers, of which the speciality was the transport and rapid construction of floating bridges in ‘First Line’. In November 1866 I marched to Chatham with this Troop, and we spent an instructive and very pleasant year there, returning to Aldershot on November 1867.While my troop was at Chatham in the summer of 1867, our higher authorities decided that our pontoon bridge equipment was unsatisfactory in some particulars, and invited officers to submit designs for a new pattern. So I submitted a new design which was approved for trial, and sometime after my troop returned to Aldershot in November 1867, I was sent back to Chatham to carry out the necessary manufacture and experiments under the orders of the R.E. Committee, which then attended to such matters. I remained at Chatham, with a short interval at Aldershot in 1870, until I went to India in 1871, the new pontoon equipment being finally adopted in 1870
Trivia alert: Winston Churchill served under Binden Blood in the Malakand Field Force.
Described in the Treatise on Military Carriages and other manufactures of the Royal Carriage Department;
The pontoon can be used either as a pontoon on a bridge or as a boat: Its outside dimensions are 21’1” x 5’1” x 2’6.5” in depth; its weight is 7cwt 1qr 0lbs., and its tonnage 9.685 tons. In horizontal section it is rectangular, its sides are nearly straight and vertical, and its ends rounded. The framework, which is very light, is of yellow deal and rock elm, the straight parts being made of the former, and the bent of the latter. The frame is boarded over with yellow pine, and each side of the boarding covered with canvas attached by India rubber solvent. The canvas is covered with marine glue before the pontoon is painted, and the bottom protected by four longitudinal ribs shod with iron friction plates. The pontoon has eight wooden handles along each side, about half way up, six attached by rope grummets and two by wire, the latter serving as eyes to receive lashing ropes, it has also a ring at each end for a cable, and is fitted with four rowlocks along the gunwale at each side, and at each end with one for a steering oar; it also has fitments for securing the saddle beam
Why did we return to the open boat design?
Experience of the tubular designs showed that should they be more than half submerged they became unstable and difficult to handle. One idea to counter this was to make the pontoons triangular in nature so that as they were depressed by passing loads a greater volume would be immersed and this form a more stable and increasing counter force. It was a good idea but impractical with construction techniques of the time so the conventional open boat design was returned.In fact, the numerous European armies had never adopted the British closed pontoon method and given their significant pontoon experience, especially the Dutch and French, this was obviously a case of experience winning out over new designs.
The Blood Pontoon did have a number of important features, instead of loading the bridge decking baulks onto the pontoons gunwales as the French preferred a separate longitudinal saddle beam was fitted, as the Austrians preferred. This saddle beam could be easily removed if the pontoon was to be used as a conventional boat.A comparison of the various pontoons in use by contemporary armies can be seen in the image below;
At about this time, the Royal Engineers, in common with many European armies, formed dedicated Pontoon Troops. These were amongst the largest soldiers in the Army because they needed to be physically able to lift the heavy pontoon equipments. These specially constituted units acquitted themselves well in the South African wars and by virtue of their size and power, won no less than thirteen inter service tug of war championships!
A development of the Blood Pontoon that was to be retained in service until 1924 was the Mark II Pontoon or Clauson Pontoon.
Named after Lt JE Clauson RE, the modified pontoon essentially cut the Blood pontoon in half, going back to the multi section design of the earlier Pasley Pontoon and the very successful Austrian Birago Pontoon. Instead of two identical sections, the Clauson pontoon used a pointed bow and square stern configuration. The two sections could be used independently or joined together using phosphor bronze fittings and this flexibility allowed a range of bridge configurations to be used, light infantry types or heavier types for wagons and vehicles for example, modularity in action.
Herman Haupt published an excellent book on military bridging in the US Civil War in 1864, click here to read. Much of the equipment used in the Civil War was based on European designs and the book provides an excellent reference.
The images below show the Mk II pontoon in action in WWI.
Some arrangement is needed to provide access from the river bank to the pontoon bridge deck, especially important if the bank is higher than the deck or the river is tidal. The Austrian Birago Trestle was used until 1890 although this video clip of the Austrian Army in 1939 shows what would seem to be a Birago Trestle in use!
The Birago trestle was replaced by the Weldon Trestle
At the start of WWI, the two Bridging Trains were equipped with Mark II Pontoons and Weldon Trestles in addition to a number of Light Raft Equipment, derived from a much earlier design.
Developments during WWI included the introduction of the Marston Lever Trestle and Mark IV Trestle. As vehicles and artillery increased in weight it was obvious that the floating bridging equipment would need to change to accommodate them.
Included in these developments were the Mark III Pontoon, a Mark II with different cladding and the Mark V Trestle that remained in service until the 1920’s.
During the war a number of floating bridges were designed and used but in relatively small numbers, these included the Sankey Type B Bridge that used steel joists instead of timber baulks on the Mark II Ponton and the Heavy Steel Pontoon.
The next major advance was the Inglis Heavy Floating Bridge, unique at the time because it used a continuous girder design to spread the load over a number of the newer Heavy Pontoons. Despite being a significant advance it was not taken into service, the war only having recently ended.
In the late twenties a series of equipment upgrades saw the introduction of a number of new pontoons and trestles including the Mark IV Pontoon and Mark V Trestle. The Mark IV pontoon was completely enclosed and used a type of plywood called Consuta and so the pontoon was often called a Consuta Pontoon with a safe buoyancy of 6.5 tonnes. The Mark V Trestle used mild steel instead of wood.
The Mark VI Trestle was much stronger and introduced in 1929.
Trestles could be used without pontoons for short gaps.
British Pathe clip of what looks like a Mark IV or V pontoon in use here
Kapok Assault Bridge
The Kapok Assault Bridge was an infantry bridge designed following the extensive use of improvised floating bridges during WWI. Instead of any convenient materials, petrol cans and cork, as used during the Great War, the Kapok Assault Bridge used a kapok filled canvas float and timber footwalks. The US Army also had their own version.
The floats were each 6 foot 6 inches long and decking sections were 6 foot 6 inches long and 1 foot 10½ inches wide.
The training pamphlet describes the construction process;
Two men carried each float and one man carried each length of decking. A float was attached to each end of a length of decking using simple catches. The completed bay was then pushed out into the water. A second decking section was attached to the shore end of the first bay and then a float was attached. The bridge was progressively pushed out into the water until the far bank was reached. The maximum practical length was 150 foot, but this was only in still water. Any tide, current, flow or wind would make this length hazardous or impossible.
Thirty bays of kapok bridge could be carried in a 3ton GS lorry
Folding Boat Equipment (FBE)
The FBE was adopted by the Army in 1928 and through a number of versions improved; it was still widely used in WWII where it often complimented the Bailey Pontoon. It was designed to provide a means of getting light vehicles over a river in the immediate support of an assault, taking much less time to construct than the Heavy Pontoon it was inevitably less sturdy but perfectly matched to its task.
The design of the boat was quite ingenious, when folded it was completely flat for ease of transport and storage and used a continuous fabric hinge. The boat itself could carry 16 men either rowing or using a Coventry Victor 7.5hp outboard motor. In overload condition, up to 30 men could be carried although it would be low in the water.
With the addition of a range of deck and connecting equipment the basic folding boat could be used as the FBE Tracked Raft, FBE Decked Raft and FBE Bridge.
THE FBE Tracked Raft could support vehicles up to 3 tonnes in weight and used two boats, a pair of wooden transoms and 6 trackways. The centre pair of trackways were 14ft long and the front and rear loading ramps were shorter, at 9ft long
The FBE Decked Raft used 3 boats and larger ramps with a capacity of 4.5 tonnes.
The FBE Bridge consisted of multiple connected FBE Decked Rafts to form a continuous bridge span, the FBE Trestle and reconnaissance folding dinghy completed the set.
The FBE equipment was improved in the early thirties, the Mk II design only a minor change but the 1939 Mk III, that was to see extensive service in WWII, was a significant improvement, moving the capacity up to Class 9.
The Mk III FBE could also be used in a number of configurations including the Class 5 Decked Raft, Class 9 Decked Raft and Class 9 Shore Loading Decked Raft. Any of these could be used as a powered raft using outboard motors. Finally, the Class 9 bridge consisted of a number of decked rafts connected together with each end using a half floating bay and FBE Trestle, much like the Mk I variant.
The Mk III decked variants used steel Road Bearers that weighed 380lbs each, shown below) and 3ft 10.5 inch deck panels of Douglas Fir. Bay connectors were designed to limit deflection under load and the Mk III FBE Trestle was improved to cope with Class 9 loads.
Additional images of the Mk III Folding Boat Equipment in use during WWII are shown below;
FBE Mk III Boat
FBE Mk III Bridge
Mk III FBE Ferry
Another clip from British Pathe shows both the FBE and Small Box Girder bridge under construction in a scene that looks identical to the image above.
Bailey Pontoon and Raft
I will of course be covering the iconic Bailey Bridge in some detail in a later post but the design was so adaptable it was also used in both floating pontoon and raft configurations. Because the Bailey does not have any projections below the bottom chord it was soon realised this would make it ideal for use with pontoons and design work commenced in 1941.
The final configuration used a 30ft single-single Bailey bay supported on two pontoons.
These pontoons comprised three sections, front and rear were the existing Mark V Pontoons but a new Bailey Centre Pontoon was designed and introduced to enable the greater weights to be supported.
The sections were connected using a semi flexible connector that provided a degree of movement and the necessary rigidity to spread loads across the entire structure.
A key feature of the Bailey Pontoon was its landing pier; this was a single span from the bank to the bridge level and eliminated the need for unwieldy and unreliable bridge trestles. 4 Pontoons assemblies were used on the landing pier and this can be clearly seen in the image below.
The Bailey Pontoon was constructed by floating completed sections into place with the assistance of small boats,
often a Royal navy PN boat as per the image below
The standard Bailey Pontoon was Class 40 but this could be increased to Class 70 by doubling up (more on this later) and using additional pontoons.
Class 50/60 Raft
As versatile as the Bailey bridge was it did not lend itself to rapid construction of rafting equipment especially during the early stages of a river assault. The existing FBE was quicker but did not have the load carrying capacity for anything but light vehicles so in 1943 a new design study commenced to create a raft capable of rapid construction and with a load carrying capacity sufficient for a Churchill tank.
To make building quicker and simpler each pontoon was identical and carried its own superstructure of two folding panels. The raft could be operated with 22hp Johnson outboard motors or unpowered using boats, DUKW’s or shores based winches, often borrowed from the RAF.
Post War Rafts
With a greater abundance of raw materials and the availability of modern alloys a number of improved rafts and ferries were developed including the Light Assault Raft and the Light Assault Floating Bridge, the latter being the first military bridge to utilise hydraulic articulators.
The LAFB was designed to carry all the vehicles and equipment of an Infantry Division (not all at once though!) and a scaled up version, not surprisingly called the Heavy Assault Floating Bridge was introduced in in the same post war period although it was not until 1962 that it actually entered service by which time the amphibious bridging equipment was looking a more acceptable proposition.
This video from British Pathe shows the LAR
The Heavy Assault Float Bridge
Design work on the Heavy Ferry, sometimes called the Class 80 Heavy Ferry, started in the late fifties as tanks started to increase in weight, again.
The Heavy Ferry comprised 3 pontoon sections, main, buoyancy and propulsion. The inner main pontoon could carry a Class 80 vehicle, the outer buoyancy pontoons provided extra lift and the propulsion pontoon powered the ferry at speeds up to 7.5 knots using a Rolls Royce B80 powered Gill waterjet system, the same engine as used on the Saladin and Saracen armoured vehicles.
From the RE Museum exhibit card;
These pontoons were connected together in the water; using spring loaded self-actuating linkages, to form a free ranging ferry with a 15ft wide roadway, 109ft long from ramp end to ramp end. The Heavy Ferry helped to solve the problem of carrying heavy support weapons across a water obstacle in time to enable assaulting infantry to repulse a enemy counter attacks. The ferry could be built in an hour in good conditions. It was capable of carrying either six 3 ton GS trucks, three 10 ton GS trucks or of course the main battle tank and could achieve ten round trips an hour across a 400ft water gap.
Modern Floating Bridges
I will look at the floating variants of the Medium Girder Bridge, Air Portable Ferry Bridge and Logistic Support Bridges in later posts.
Landing Ship Logistic and Harbour Pontoon Equipment (Mexeflote)
The Mexeflote came into service with the British Army in the early 60’s, elegant in its simplicity, they are simply pontoon sections that can be pinned together (much like the Bailey bridge) to form lighterage rafts, jetties and piers.
When used as a powered pontoon they use what are in effect, large outboard motors.
The Knights class RFA’s would carry two, one on each side. To deploy them the lashings were removed leaving a single quick release fitting holding it until the whole thing was released, the mexeflote falling into the water.
Recovery involves manoeuvring them alongside, removing the engine, winching them up over the fender belt and securing for transit.
Multiple Mexeflotes can be combined and in addition to acting as a powered raft can also be as a jetty, floating transfer platform or other floating structures. The modular construction allows a variety of shapes to be constructed.
When used as a powered raft they are usually commanded by a junior NCO with a crew of 5.
Individual pontoons are of welded steel construction with flush sides.
Built into the sides and ends of the pontoons are recessed slots into which the connectors are fitted.The bow pontoon consists of a forward section, an aft section and a ramp. The forward section is hinged to the bottom edge of the box-shaped aft section and can articulate vertically to a maximum of 457 mm above the deck level and be lowered to a maximum of 380 mm below the surface of the aft section. The manually operated, demountable articulator is mounted in a recess in the aft section and is connected to the forward section by an articulator ram.
The articulator has a safe working load in excess of 80 tonnes. The pontoon ramp is hinged to the forward section and slides over the forward end of the aft section to bridge the gap between the sections.The centre pontoon is a box-shaped unit with an internal lateral bulkhead dividing the interior into two watertight compartments.
The front ramps are hydraulically mounted and the engines/propulsion units are connected at the rear.
Total payload depends on the size of the assembled pontoon
20.12 x 7.32m 60 tonnes
8.41 x 7.32m 120 tonnes
38.41 x 12.2m 180 tonnes
The propulsion units, or outboards to you are me, are rather special.
Modular Z Drive propulsion units from Sykes Hyrdromaster provide the motive force when used as a powered raft and although it might not look particularly seaworthy can be used in 1.5m wave conditions.
In 1994 the Army ordered an additional 50 units and in 2000 upgraded most of them.
The Z Drives have now entirely been replaced with OD150N from Thrustmaster.
The pontoon sections are sized to be compatible with ISO containers and although I am not sure who made them, their construction is relatively simple so if Australia did buy Largs Bay and the mexeflotes weren’t included in the optional extras list they should be relatively easy to manufacture.
Alternatively, they could buy them from Jenkins Marine in Poole, Dorset, ironically, not all that far from Christchurch and MEXE.
The US Army Logistician Journal had a good article on the role of 17 P&M, especially how they fit into an amphibious operations, in 2005. Click here to read it.
Mexeflotes really came into their own during Operation Corporate, a hugely challenging logistic effort. The lines of communication stretched 8,000 miles or 21 sailing days from the UK and there were no plans for an operation of this scale outside of Europe.
Each of the Knights Class LSL’s had a detachment from 17 P&M and a Mexeflote or two although they were carried on the deck for the voyage south after Ascension because it was thought the severe south Atlantic weather would rip them from their side mounts.
Operating around Green Beach in San Carlos Water, mexeflotes landed a significant amount of vehicles and stores including 63 Battery RAF Regiment. After initial operations on the 20-21 May, they continued for a couple of weeks. It is estimated that the Mexeflotes offloaded some 75% of the stores and due to the weights being carried, especially ammunition pallets, the pontoons were often underwater, as the picture above.
The LSL’s were used to transfer equipment from the larger RORO vessels offshore and it is during this operation that a Mexeflote was used for at sea ship to ship transfer. Connecting the LSL and a larger ship the Mexeflote would form a floating causeway and fork lift trucks like the Fiat Allis would trundle between the two. In the sea conditions encountered this must have been a very hairy operation.
LSL’s and mexeflotes continued to be used at Teal Inlet and the ill fated Bluff Cove
Sergeant Derrick Sidney Boultby of the Royal Corps of Transport was awarded the Military Medal for his actions and his citation was as follows;
Sergeant Boultby of 17 Port Regiment, RCT, was the NCO in charge of MEXEFLOTE rafts throughout the Falkland Islands operations. At Ascension Island, during a massive re-stow operation he worked all hours under difficult conditions to move cargo quickly. In San Carlos Water, the MEXEFLOTE rafts played a major part in the logistic landing of equipment to ensure the success of the fighting troops. From the exposed position which such a raft offers, Sergeant Boultby worked continuously throughout daylight hours and in extreme weather conditions.
The vulnerability of his position to constant enemy air attack did not deter him from his task and he was an inspiration to his crew and other RCT personnel. He was coxswain of the MEXEFLOTE present at Fitzroy during the bombing of RFA SIR GALAHAD and RFA SIR TRISTRAM, and repeatedly returned to the area of the stricken ships to rescue survivors and, with complete disregard for his own safety, dived into the sea to rescue a Chinese crewman. Sergeant Boultby’s dedication to his tasks in dangerous conditions was outstanding.
Highlighting a deficiency in ship to shore fuel transfer the mexeflotes were used to move podded fuel vehicles, these would be driven off the beach, used to fill jerrycans and returned to the ship for refilling, hardly efficient but the best that was available.
After hostilities finished, mexeflotes continued to provide an essential ship to shore transfer service until more permanent facilities could be established, FIPASS for example.
In the aftermath of the earthquake in Haiti, DFiD and the armed forces supplied a number of locations with much needed food and other supplies.
Bay Class Royal Fleet Auxiliary (RFA) vessel Largs Bay, with members of 17 Port and Maritime Regiment, Royal Logistic Corps, and other members of her embarked military force delivered essential supplies at Haiti’s capital Port-au-Prince, the ship and her crew continued to work, redistributing World Food Programme (WFP) food and commodities to Haitian communities who were logistically cut off from the rest of the island in the aftermath of the quake.
Since the disaster, the population of Anse-à-Veau, in Nippes province on Haiti’s southern peninsula, was swollen by refugees from Port-au-Prince. With the roads impassable due to mudslides and flooding, the only way to get aid through to the the area has been by occasional air drops.
RFA Largs Bay and its crew were tasked by the WFP to deliver Anse-à-Veau’s first major relief package since the earthquake.
During the four-day relief operation at the village, RFA Largs Bay’s Mexeflote raft shuttled 275,000 ready meals, 30 tonnes of rice, six tonnes of beans, more than 200 boxes of corn soya blend, 100-plus boxes of vegetable oil, and 13 bags of salt to the shore at Anse-à-Veau.
For a great gallery of RFA Largs Bay and the Mexeflote in and around Haiti, click here
No, I haven’t been on the sherry,
Mexeflotes have been used for transferring vehicles from the Points class RORO vehicles to facilities at RAF Akrotiri as part of the ‘sail to fly’ movements programme.
The Joint Movements Squadron (JMS) is made up of RAF and Army personnel from 17 Port and Maritime Regiment (Royal Logistic Corps)
Read more here
The Mexeflote is an unglamorous but essential and innovative system, and its a metal box with an ISO container on the top
What’s not to like!
There had been some preliminary work on amphibious bridging equipment but this had concentrated on add on flotation units for existing vehicles. In the early sixties the idea was developed into a requirement for an amphibious bridge unit that could build a Class 60 bridge at about 400 feet per hour and to also have the flexibility to operate in raft mode under its own power.
Advantages of the amphibious bridging equipment would be the elimination of concentrations of mean and equipment at bridging sites but they would be useful for wet gaps only. Given the likely operational areas in West Germany this was a reasonable disadvantage to accept and the idea progressed.
Unfortunately no such equipment existed on the drawing board but the EWK-Gillois equipment was available and so the Royal Engineers established a trials unit.
Designed by the French Army Officer, Col Jean Gillois and manufactured by the German Eisenwerke Kaiserslautern, the EWK-Gillois was an ingenious and wholly unique concept.
The Gillois was accepted into service in 1961 but the German M2 alternative was soon introduced as a superior alternative.
The M2 was a Class 24 amphibious vehicle with the buoyancy, decking and ramps needed to construct a bridge or ferry. The side pontoons were stored and hydraulically rotated into position before entering the water. Additional stringers were stored and used for making ramps or between adjacent units. A single m2 Rig could be used as a Class 10 ferry, two rigs joined together for form a Class 30 Ferry and more combined for a maximum of Class 60. The in service M2B’s were converted to M2D’s that raised the carrying capacity to MLC70 Tracked and MLC93 Wheeled.
General Staff Requirement 3987 – A Deliberate West Support Bridge outlined what was to become the M3 Rig. The M3 was a collaborative development between the UK and Germany, the UK eventually taking 38 units in 1999, each one costing £1.2million.
The M3 is basically an improved all round M2, greater load carrying capacity (up to MLC 70 tracked and 100 Wheeled) and faster into use. In comparison, the M3 can be used to build a 100m bridge in 20 minutes using 24 men, the M2 would need 48 men, take twice as long and need a greater number of vehicles.
Despite this, the Amphibious Regiment and now Squadron is relatively complex requiring combat support boats, divers and an extensive REME workshop.
Despite being used in action in Iraq, with the latest round of cuts the M3 rigs will be placed into extended readiness.
Click here for the General Dynamics M3 Brochure.
Infantry Assault Bridge (IAB)
To end this post on floating bridging equipment is the IAB, although strictly speaking it does not always operate in floating mode, its clear span being quite large
The float is used to assist with launching and it can be used to extend the bridged distance.
Additional images from General Dynamics
The IAB has seen extensive service in Afghanistan and is an obvious improvement on the Kapok Assault Bridge!
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