The Bailey bridge

Wars are won by the obvious weapons, and remembered by them: the tank, the bomber, the carrier. But the weapons that decide the pace of a campaign are usually the quiet ones, designed not in laboratories but in draughty huts by salaried men who go home at five. A bridge is not a weapon in the ordinary sense. It fires nothing. It is simply the means by which an army that has reached a river is not stopped by the river. In the mechanised war of 1940 onwards, when divisions moved at the speed of their fuel and not the speed of their feet, the bridge became the limiting reagent of strategy. The man who solved it was a Yorkshire railway clerk's son who had spent twelve years quietly improving Army trestles in a shed by the Stour.

THE CLERK FROM ROTHERHAM

Donald Coleman Bailey was born at Rotherham on the fifteenth of September 1901, son of Joseph Bailey, clerk on the Great Central Railway, and Janet Coleman. The household was of the steady professional sort the West Riding produced in great quantity: chapel, ledgers, evening study, a son sent to the Leys School at Cambridge and then to Sheffield for a BSc in civil engineering, taken in 1923. Four years with Sir Robert McAlpine and Sons in Hammersmith taught him how a contractor actually puts steel across water, which is not the same as how a university teaches it. In 1928 he went down to Christchurch in Hampshire, to the War Office's Experimental Bridging Establishment on the bank of the Stour, and there he stayed. He was a civilian. He drew a civil servant's salary. For twelve years he tested trestles, refined the Inglis bridge, watched sappers heave timber baulks into rivers, and filled notebooks with the small disappointments of a discipline nobody outside it could be made to care about.

The bridge then in service was Charles Inglis's, designed in 1916 at the Royal Engineers College at Chatham: a pyramid-trussed affair of timber and steel, about a hundred-foot span, Class 3 capacity. It would carry a Bren-carrier. It would not carry a Matilda. It took six hours and twenty trained engineers to assemble, much of that with the bridging party exposed on the far bank. In peacetime this had been acceptable. In May 1940, when the British Expeditionary Force fell back through Belgium and northern France towards Dunkirk, the after-action reports came home with one complaint above all others: the bridges were too slow. Armoured columns reached water and stopped. The Wehrmacht did not stop at water. The Wehrmacht had pontoon trains that crossed in forty minutes and a doctrine that did not wait for the engineers.

THE HUT BY THE STOUR

Friday, the fourteenth of February 1941. The pale Hampshire light of mid-afternoon, the river running cold and brown outside, a coke stove in the corner of the wooden hut, a draughtsman's bench under the window. On the bench: a working drawing of a modified Inglis, a stack of Ministry of Supply correspondence weighted by a paperweight, two pencils, a slide rule. Bailey is thirty-nine years old. He is in his shirtsleeves. He has been turning the same problem over for nine months, since the BEF reports first came across his bench in the summer of 1940, and the turning has by now worn a groove in his thinking.

The problem, stated plainly, is this: a bridge of forty-eight tons capacity must be put across a sixty-foot gap, in under an hour, by an infantry party working from one bank only, without cranes, without skilled engineer labour, without scaffolding in the water. The Inglis cannot do it. No bridge in any army's inventory can do it. The Germans, who in this respect are ahead of everyone, do it with pontoon trains and specialist troops, and even they take longer than an hour for a forty-eight-ton load.

A SECOND OF TIME IN HISTORY

He turns the problem in his head one more time, the way an engineer turns a casting in his hands to find the seam. If the bridge cannot be carried whole, it must come in pieces. If the pieces must be carried by men and not cranes, each piece must weigh no more than four men can lift, which is to say six hundred pounds. If the pieces must bolt together without skilled labour, the joint must be a pin in a lug, struck home with a maul. If the bridge must carry any required load over any required span, the pieces must be identical and stackable, so that strength is added by repetition: two panels side by side for a heavier load, two storeys high for a longer span, three by three for the Sherman. The whole grammar of the thing falls into place in the time it takes to set down a pencil and pick it up again. He reaches for the nearest piece of clean paper, which is the back of a Ministry of Supply envelope from the morning's post, and he sketches.

A rectangular panel, ten feet long, about five feet high. Welded-steel framework. Triangulated, because triangulation is what makes a truss a truss. Three lugs along each vertical edge, bored for a bolt-end pin. The pin is the secret. The pin makes the panel a module. The module makes the bridge indefinite. Width adds load. Storeys add span. The sketch takes him perhaps fifteen minutes. There is no drama in the hut. The coke stove ticks. Somewhere outside a sapper is shouting at another sapper about a winch. Bailey puts the envelope down on the bench, weights it with the slide rule, and at twenty to five he puts on his coat and walks home along the Stour to his tea.

He does not, that evening, know what he has done. He knows only that he has at last got it into a shape that can be built. The men who will lay these panels across the Volturno and the Sangro and the Rhine are at this moment still in their training depots, or at school. The bridge has not yet got its name.

CHRISTCHURCH TO WHITEHALL

The prototype was assembled on the meadow at Christchurch in the early spring and launched across the Stour on the second of May 1941. It went over by the method Bailey had specified: a nose of light panels rolled out on rollers from one bank, counterweighted by the heavier panels behind, the whole structure cantilevered into space until it tipped down on to the far abutment. No man entered the water. No crane was used. The bridging party were ordinary sappers, not engineers. Sir Alec Bedford of the Ministry of Supply, watching from the bank, is recorded as saying it was the most useful afternoon he had spent in the war. In July the Army Council ordered the design into production. By the close of 1941 the factories of Birmingham and Sheffield were rolling out panels at a rate of several hundred a week.

The Royal Engineers took to it as men take to a tool that has been waiting for them. A standard Bailey could be put across a sixty-foot gap, Class 40, in under forty minutes by a platoon of thirty-six. The grammar Bailey had set down on the envelope absorbed every variation a campaign could ask of it: double-single, double-double, triple-double, the panels stacked and strapped until you had a structure that would carry a Churchill or span the Rhine.

THE BRIDGES OF THE WAR

In North Africa they laid them across wadis. In Italy, where every river ran north to south across the line of advance and every retreating German engineer had been thorough, they laid them by the hundred: at the Volturno, the Garigliano, the Sangro, the Rapido at Cassino. At Sicily the Eighth Army crossed the Simeto on a Bailey within twelve hours of taking the far bank. In Normandy after D-Day the British and American armies between them laid over fifteen hundred Bailey bridges in the eleven months to VE Day. The largest was thrown across the Rhine at Wesel in March 1945 by the Royal Engineers of the British Second Army: one thousand two hundred and seventeen feet of panel, assembled in thirty-six hours under intermittent shellfire, the longest Bailey ever built in war.

Eisenhower, asked in 1945 what equipment had most helped to win the campaign in the west, named three things: the bulldozer, the jeep, and the Bailey bridge. The phrasing in his recorded remark is that they were the three pieces of equipment that contributed most to our victory in Africa and Europe. Montgomery, who was sparing with praise of civilians, wrote that without the Bailey bridge it is very doubtful whether we should have been able to cross Italy.

THE RETURN

Donald Bailey was appointed OBE in 1944 and knighted in the 1946 New Year Honours. He did not leave Christchurch. He stayed at the Experimental Bridging Establishment, by the same river, in much the same hut, and went on improving the bridge until his retirement in 1966. He had no taste for London, and the gentlemen of the Ministry came down to him. He died at his home in Bournemouth on the fifth of May 1985, aged eighty-three. The Stour, which had carried his prototype, ran past the end of his garden.

The bridge outlived him, and outlived the war it was made for. It remained in British service until 1990, when the Medium Girder Bridge of the 1970s at last displaced it. Israeli, Indian, Pakistani and a dozen other armies kept it on into the twenty-first century. In civilian use it became the standard emergency bridge of the world: dropped into Nepalese valleys after earthquakes, across Louisiana bayous after hurricanes, over Italian rivers after floods. The Mabey works in Lydney still rolls out somewhere near a thousand panels a year, identical in geometry to the rectangle Bailey set down on his envelope.

Greatness is not always the property of those who set out to be great. Sometimes it is the property of a salaried man who, on a Friday afternoon in February, has the patience to keep turning a problem until it falls into a shape that a stranger with a spanner can build. On the wall of the Priory church at Christchurch, a few hundred yards from where the hut once stood, there is a small brass plaque to Sir Donald Bailey, and on the meadow by the Stour the abutments of the first launch still stand in the grass, square and unremarked, of a piece with the bridge they once carried away.