Operation Neptune

by Kenneth Edwards

  It was inevitable that much of the shipbuilding and nearly all the alteration work should be done in the crowded shipyards of the United Kingdom. Although shipyards in the United States and Canada were also working “all out” for D-day, their work was predominantly one of production. In 1943 the United States shipyards turned out no less than 21,525 landing craft, and did this on a rapidly rising production schedule which was still soaring after D-day in Normandy. By no means all the American-produced landing craft were, however, allocated to the European theatre of operations, for the swing to the offensive in the Pacific was calling more and more urgently for landing craft. The contribution from across the Atlantic in landing craft for the invasion of Normandy was, however, great and vital. In most cases these landing craft made the voyage across the Atlantic under their own power, and a number of very daring and gallant voyages were made in these little craft. Before the war such voyages would have been “front page news” throughout the world, but they were shrouded in the essential secrecy which cloaked all the invasion preparations.

  For all the effort expended on the western side of the Atlantic the British production in landing craft was prodigious. Its rapid growth from very small beginnings was illustrated by the following sentence—carefully phrased to avoid giving total figures—used by the First Lord of the Admiralty when presenting Navy Estimates to Parliament on 7 March 1945:

  “In the first quarter of 1942 four times as many major landing craft were built as in the first quarter of 1941; in the first quarter of 1943 ten times as many; and in the first quarter of 1944 sixteen times as many.”

  As the plans advanced it was appreciated that even the combined facilities of the southern ports of England would not be sufficient to handle the vast cross-Channel traffic which was contemplated. Fortunately the design of tank landing craft and tank landing ships, with ramps in the bows which had been dictated by the need for disembarking their loads on open beaches, simplified the loading problem. Instead of having to build jetties and supply them with cranes, loading facilities for those craft could be produced in Britain by the building of “hards.” These are, in effect, hard roadways sloping down into the sea. The LCT’s and LST’s could nose in against them, let down their ramps, and the tanks and vehicles could be driven straight into the ships. A very large number of these “hards” had to be built along the south coast of England to ease the pressure on the established port facilities and, incidentally, they greatly reduced the time of loading these craft.

  Meanwhile there were under construction in the United Kingdom the components of a project which has been described as the greatest constructional engineering feat in history.

  So long as an invading army has no efficient port at its back and is dependent upon reinforcements and supplies landed over open beaches, its reinforcements and supplies must be to a great extent at the mercy of the vicissitudes of the weather. It is quite true to say, therefore, that even the first phase of invasion and the firm establishment of the invading army cannot be called successful until the invaders are in possession of a port.

  This fact had greatly exercised the planners from the very outset of their task. The ideal would, of course, be to capture a major port in the initial assault, but the enemy well appreciated the importance of the ports and had specially strengthened their defences. The experience of the Dieppe raid and all subsequent intelligence went to prove that the ideal would not be attainable against an enemy of Germany’s calibre. The alternative was to land on beaches where the configuration of the coast would give good shelter against the prevailing winds, and with ports in the vicinity which might be captured within a reasonable time after the initial landings. It had been these factors which had been chiefly responsible for the selection of the Bay of the Seine area for the invasion of Northern France. It was hoped to be able to capture the port of Caen and the canal leading to it very early in the operation, and within a reasonable period to cut off and capture the great port of Cherbourg. These, however, could not be guaranteed—and invasion cannot be undertaken on a gambler’s charter.

  It was at this early stage that Commodore Hughes-Hallett, then head of the “X Staff” planning the invasion, had his great idea. It was not a new conception, but a development of a technique. He argued that since urgency had shown it to be possible to prefabricate most big structures it should be possible to prefabricate a port, take it in sections across the Channel, and set it up for use off the invasion coast. If the sections were ready this could be done in a few days and with a degree of certainty which could not exist in estimating the date on which a very strong position held by the enemy could be captured, to say nothing of the damage which the enemy would almost certainly do to a port before being driven out. Moreover, it was already becoming clear that the projected invasion of Normandy was so gigantic an undertaking that even the capture of one major port in virtually undamaged condition would not give sufficient port capacity for the enormous quantity of stores and equipment which it would be necessary to land. It was estimated that even in the early stages of the invasion about 12,000 tons of stores and 2,500 laden vehicles of all shapes and sizes would have to be landed every day—a commitment which took no account of the reinforcing troops to be put ashore and which would be increased as the size of our armies in France grew. Those figures were then regarded as the absolute minimum for a period of 90 days after D-day.

  The question of whether to recommend the construction of the great artificial harbours was considered in detail at a meeting in London in June, 1943, which was held under the chairmanship of Admiral Lord Louis Mountbatten, then Chief of Combined Operations. This meeting decided that artificial harbours would be essential to provide sheltered water off the beaches to enable a sufficient quantity of stores and equipment to be put ashore irrespective of the capture of ports and of weather conditions. The decision of this meeting was at once submitted to the Combined Chiefs of Staff, who were then in session at Quebec and considering the “COSSAC Plan” for the invasion of Northern France.

  The Combined Chiefs of Staff examined the proposal, found it both ingenious and necessary, and gave their approval. Thereupon, technical experts from the Admiralty and War Office were telegraphed for, and they flew to America to co-ordinate the plans for the artificial harbours in the light of the resources available. These technicians finished their deliberations by 3 September 1943, and submitted their findings to the Combined Chiefs of Staff, then in Washington. These were approved by the Combined Chiefs of Staff, who gave the order to proceed with the prefabrication of the harbours with all dispatch.

  It was recognised that time was desperately short for the completion of so great a project, and that shortage of time would prevent exhaustive tests of the completed sections before they had to be ready for use, so that many of the components of the artificial harbours would have only theoretical soundness, backed as far as possible by experience gained with models in the National Physical Laboratory. It was understood from the beginning, therefore, that risks would have to be taken, but so important were the harbours and so short the time, that these risks were deemed to be fully justified.

  Had unlimited time been available it is possible that so long a period would have been occupied in experiments and tests that much the same degree of urgency would have arisen in the final production of the sections of the prefabricated harbours. This happened in the case of floating piers which, it was decided, were to form part of the synthetic harbours. The problem of producing a floating pier which would be strong enough to rest on the beach at low tide and float on a rising tide and at the same time be sufficiently flexible to withstand the surge and twisting motion which the waves would impose upon it had been under investigation since early in the war, but no definite results had come of the hundreds of experiments carried out. It was not until the Prime Minister took a personal interest and circulated a minute on the subject, making it quite clear that he would brook no further delay, that solutions began to be found. In this mi
nute Mr Winston Churchill wrote:

  “Piers for use on beaches: They must float up and down with the tide. The anchor problem must be mastered. . . . Let me have the best solution worked out. Don’t argue the matter. The difficulties will argue for themselves.”

  Although the problems of man-power and of material resources were much greater in the United Kingdom than in the United States it was considered essential that both the projected artificial harbours—one for use off the British section of the invasion beaches and one for use off the American sector—should be constructed in Britain. Such a decision was dictated by the well-nigh insoluble difficulties which would have arisen if the enormous sections of the synthetic ports had been constructed in the United States and had to be conveyed across the Atlantic.

  The design of the artificial harbours—which were given the code name of “Mulberries”—consisted of an outer floating breakwater of “bombardons,” an inner fixed breakwater made of concrete caissons, and floating piers running out from the beaches to “spud pierheads” against which ships could lie. Each “Mulberry” was to provide a harbour roughly the size of that at Dover. For technical reasons the concrete caissons forming the fixed breakwater could not be laid in water deeper than five and a half fathoms, but this would allow ocean-going ships of the “Liberty” type to use the inner harbour, while bigger vessels could use the somewhat less sheltered water inside the floating breakwaters.

  When the bombed and burnt-out liner Georgic was being salved at Suez, the salvage authorities had great difficulty in securing the necessary amount of concrete because all concrete belonged to the military authorities. It was presumably for much the same reason that the War Office was entrusted with the design of the concrete caissons for the “Mulberries,” although the task of taking them to France and sinking them in position was a naval responsibility, and they were to be sunk far below high-water mark—the usual line of demarcation between naval and military responsibilities. As a result of this decision there were unnecessary delays and last minute alterations had to be made. In fact, the “Mulberry” caissons would not have been ready if D-day had not had to be postponed by one month in order to meet General Montgomery’s requirement of a landing on a wider front.

  The naval planning staff, who had to arrange for the sinking of the caissons in the correct positions, had specified that these should be fitted with flooding apertures which would enable them to be sunk in fifteen minutes—the time for which it was estimated that they could be held accurately in position against varying tidal and weather conditions. The first caissons produced to the War Office designs took an hour and a half to sink. Nor was the War Office in a position to appreciate the towing problem involved, and the caissons were fitted with quite inadequate towing arrangements. These were only made efficient at the last moment by the employment of every rigger in Chatham Naval Dockyard. The sinking time for the largest type of caisson was finally reduced to 22 minutes.

  These were, however, minor breakdowns which could be, and were, put right in time. It would have been truly miraculous if no detail had gone wrong in carrying out so gigantic a proposition.

  The greatest constructional feat required was the building of the concrete caissons, which was carried out under Ministry of Supply arrangements, the Ministry of Labour having to draft many thousands of workers into the areas where the caissons were to be built.

  The “Mulberries” demanded the construction of no less than 146 of these caissons. They had to be of different sizes to suit the different depths of water in which they were to be sunk, and it was decided to make six different sizes. The largest size had a displacement of 6,044 tons, and the smallest size a displacement of 1,672 tons. It was estimated that their construction required 330,000 cubic yards of concrete, weighing nearly 600,000 tons; 31,000 tons of steel; and a million and a half superficial yards of steel shuttering.

  One of the major problems was where to build these great reinforced concrete structures, for they would have to be launched in the same way as a ship and practically every permanent and improvised slipway in the country was fully occupied with shipbuilding or the assembly of prefabricated landing craft.

  A survey of the facilities for building structures of this sort showed that there were available only four suitable slipways in the whole country. It would be possible to build these caissons in dry docks, but only eight of these could be made available. Some types of caissons could be built in wet docks, but these were almost all in use for the loading and unloading of ships and only two could be allocated to the task of building the “Mulberry” caissons.

  Those were the total building facilities available, and they were so inadequate for the task that it was doubtful whether, in the time available, they could produce more than about half the caissons required.

  Two large Mulberry caissons under construction in a dry dock. The quality of this image is poor, but few photographs survive of the caissons being built. The job kept 20,000 British workers working at top speed; 865,000 tons of reinforced concrete had to be cast in six months.

  Such was the disheartening position when somebody, actuated by the great driving force behind all the invasion preparations, had a brilliant idea. If it was possible to improvise slipways for landing craft construction why should it not be possible to improvise dry docks in which the great concrete caissons could be built? Why indeed? In normal times there would doubtless have been every sort of objection, but the times were not normal, and the solution of this problem had the same Elizabethan quality as the conversion of mean streets into emergency shipyards.

  A Mulberry caisson under construction in a temporary scooped out ‘dry dock’ off the Beaulieu River.

  At twelve places close to the Thames mechanical excavators got to work and scooped out twelve great holes in the ground. Their depth was far below the river level at high tide, and, the ground being very porous, pumps had to be installed to keep these great pits dry—or nearly dry. In those pits began the construction of the lower portions of the concrete caissons required for the “Mulberries.” When these had reached a stage at which they would float and only the upper sections and fittings needed to be added, the pumps were stopped and excavators removed the strip of land between the pit and the river. Thus the pit was flooded and the under-water sections of the caissons could be floated out into the river. They called these pits basins, but they did not become basins until they had served their primary purpose. In effect they were improvised graving dry docks, with the strip of soil remaining between them and the river until the work on the under-water sections of the “Mulberry” sections had been completed serving as a natural caisson closing the entrance to the dock.

  One of the Beaulieu caissons afloat.

  Here was improvisation on a truly grand scale. The men concerned—20,000 workers and hundreds of designers, planners and organisers—were too busy and too intent upon the great job in hand to have time to think. If they had been able to think beyond their minute to minute service they could hardly have failed to recognise the significance of these great aids to the liberation of Europe and defeat of Germany being built in craters bigger than any ever produced by German bombs in the tortured soil of the banks of the lower Thames.

  The importance of this system of improvised dry docks for the building of caissons cannot be over-estimated. Without them there could have been no “Mulberries,” and it is safe to say that without the great artificial harbour erected off Arromanches on the Normandy coast our armies would have had to wait upon their supplies instead of being able to exploit to the utmost every sign of weakness or indecision shown by the enemy.

  The importance of these so-called “basins” in the general scheme of production of the great concrete caissons for the artificial harbours is also obvious from the statistics. A total of 146 of these reinforced concrete caissons were built for the two artificial harbours. As has been said, these were in five sizes. Sixty of the largest size displacing over 6,000 tons each were built, and
the numbers of the smaller sizes diminished to only 10 of the smallest size, displacing over 1,600 tons. Thus the biggest demand was for the largest caissons.

  Of the 146 caissons built, 57 were built in the eight existing dry docks which could be set aside for the purpose, while 23 were built on the four available existing slipways and 18 in the two wet docks which were suitable and could be spared for this work. The whole of the remainder—48 caissons, among them many of the largest size—were built in the pits excavated along the banks of the Thames, officially called “basins.”

  Each of the caissons was in some sense a ship, for it was provided with quarters for the crew which was to man it during its cross-Channel voyage. Most of the caissons, too, were armed. They had mounted on them a Bofors gun and a shelter for the gun’s crew, while stowage for 20 tons of ammunition was built within the upper part of the concrete structure. These guns would form a valuable addition to the anti-aircraft defences of the harbour, for it was to be expected that the Luftwaffe would make determined attacks on them and on the shipping which they sheltered.

  While the concrete caissons were under construction the prefabrication of sections of the road piers and the building of the “spud pierheads” went forward.

  Despite the progress made as a result of the Prime Minister’s energising minute, many problems had to be solved. It is no easy matter to produce a pier hundreds of feet long that can be assembled with its inshore end on a very gradually shelving beach where the rise and fall of the tide is over 20 feet, so that at low water a great length of the pier will be resting on sand, or possibly even rock. Floating pontoons of steel and concrete were, however, evolved to meet these requirements and the great flexible roadway was laid upon these pontoons, which were of two types and known as “Whales” and “Beetles.”