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Bill Thayer

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Chapter 4

This webpage reproduces a chapter of

Force Mulberry
Alfred Stanford
[Commander, U. S. N. R.]

published by
William Morrow and Company
New York

The text is in the public domain.

This page has been carefully proofread
and I believe it to be free of errors.
If you find a mistake though,
please let me know!


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Chapter 6
This site is not affiliated with the US Naval Academy.

 p63  Chapter V

"The magnitude of the job is unprecedented. . . ."

". . . solution requires construction of approximately 150 units, each equivalent to a 5‑story building at a site which is now not known and for which labor must be recruited. The magnitude of the job is unprecedented and it can be accomplished only under the highest priority. . . ."

— CCS 307/2
Sept. 1943

The human complications erected in the path of Mulberry with the deep tangle of command, highest secrecy, lack of communications, and all but impossible time goals, made it almost a pleasure to study the physical design of the harbor and the blueprints of the structures themselves. The clean mind of the engineer, released from the restraints of materials or cost, soared free of men's ordinary thinking and dealt now in the huge quantities and dimensions ironically only possible in the urgency of war.

 p64  To move toward the reality of the job was a constant necessity and source of stimulation in Mulberry work. There were always simple, if large and stubborn, facts.

At some point on the ever-mysterious Far Shore there were facts of geography and tides. There were certain acres of a long flat slope of a particular beach. It was out of the necessities of the earth and water at this very point that the thinking about Mulberry structures had to spring.

There was a particular site where American men from Kansas, Idaho, Texas and Brooklyn, with rifles held high and with the water about them chipped by bullets, would one day splash their hazardous way ashore. There supplies and guns and vehicles one day would follow them and roll away inland in a trail of dust.

This now unsuspecting historic area could be precisely located on a map. It lay at the foot of a table‑top cliff near the small villages of Colleville, St. Laurent and Vierville-sur‑mer on the Cotentin Peninsula. From the western end of where Mulberry A was to begin, along the foot of the cliffs there was a brief level area of several hundred yards. At the seaward edge of this interval, a two‑way asphalt road was said to run east about half the distance the harbor would occupy. Then the road dwindled to a one‑way road as it moved east, became a minor road, and finally a trail.

The villages of Colleville, Vierville and St. Laurent were back a mile or so inland. There was little life or habitation directly on the cliffs or on the shore. But back of the road that skirted the water's edge stood a few odd summer cottages. A low sea wall approximately six feet high protected the road from the Baie de la Seine. Below this wall the beach was rocky, then yielded to a long stretch of flat sand.

 p65  One longed hungrily for more details of this mysterious spot toward which all the mighty effort of the free world was focused. Too obvious reconnaissance from the air or surface would betray Allied interest and excite German suspicions to the point of strengthening existing dugouts, strong points, mines and beach obstacles. So the picture had to form very gradually, bit by bit, from low oblique air photos taken at widely separated intervals and from fragmentary ground reports.

A British submarine got in and ran one line of soundings off the American beach. These soundings showed the depth contours changed from the data on French and Admiralty charts, which in turn were based on French sailing charts of the 1890's. The changes were due, as one would suspect, to the scouring effect of strong tides (up to 3 knots) on a sandy shore. Each new storm would alter a beach like that, introducing new shoals, new runnels and flats.

From here on the planner left the area of simple facts; for however one might long for a more complete knowledge of the area, or stare at air photographs of the monotonously level cliff line, the small splashes of shadow that might be concrete strong points on the shore, or the dots in the rippling waves offshore that might be steel obstacles to pierce approach landing craft, one in the end was forced to return to just the precise facts that were facts. Beyond could only be wonder and a little awe at the peacefulness of the scene, and a technical surety that a survey party must start work practically with the first assault wave to have the complete data needed for siting such huge and complex objects as were proposed.

Still, the beach was a specific spot on a map. There were  p66 the shoreline and the road net back into the interior. One could measure out 3,000 to 4,000 feet from high-water mark on the shore and draw a line 13,000 feet long. That would be the harbor space that would become Mulberry in the fateful days ahead.

There, in the spring, a sixteen-hour day could be counted on and, in the long twilight and long pre‑dawn glow, light could be found to add to the normal day. If enemy action allowed it, the thousands of milling craft could unload their prescribed daily 8,000 tons of stores and 1,400 motor vehicles from the huge invasion fleet.

Trusting that the soundings of water depth taken so many years ago were approximately right, and brooding over the air photos, one could picture the look of the beach at various stages of the tide.

At low tide the flat sandy beach would run out from the wall alongside the road to seaward for a quarter of a mile, sloping about one foot in one hundred. With that much tide there would be occasional deep potholes and gullies. To reach depths of 12 to 18 feet when the tide was low it would be necessary to go out more than half a mile from shore. Here coasters and tugs could venture. To go out far enough for Liberty ships, which needed 28 feet depth, required the outer limit of the harbor to be placed a full 4,000 feet from the shore.

The vertical tide rise of 21 feet would cover all the quarter of a mile of beach.

One of the most difficult design problems Mulberry had to face was how to cross the flats and reach out to piers where there would always be a minimum 18 feet of water at all tides. To cross this gap from shore to piers, plans  p67 called for three lines of floating steel bridges, resting on steel and concrete pontoons. These bridges were to be made up in 80‑foot sections but towed to the site and there linked together with telescopic spans. The telescopic action of the links would accommodate the roadways to the heaving action of small waves. At low tide some of the pontoons would rest on the sand. As the 21‑foot tide came in, they would float. This floating bridging was known by the code word "Whale" and seven and a half miles of 80‑foot sections were scheduled for production in the British Isles.

These three Whales were thought of as originating at the point on the shore where the road from the village came down through a dry gully in the cliff face to join the road along the beach. This was the logical focal point for inland-bound traffic to get away in the very first days of the beach-head before new roads could be built by the engineers.

Of the three Whale roadways for the American harbor, each half a mile long, one needed to be of heavy enough construction to have a load limit of 40 tons. This would carry heavy tanks and armor. The other two Whales were to be of 25‑ton capacity, which would take the heaviest trucks, half-tracks and light armor as well as personnel and vehicles.

These three floating Whales coming out from the shore converged upon a group of six floating piers known as Lobnitz​1 piers. These piers were truly complex structures. Each pier was an oblong floating steel hull 200 feet long and 60 feet wide and 10 feet from top to bottom. In each of the four corners of a pier was a 60‑foot "spud" leg, on  p68 which the steel structure could slide up and down like an elevator. The whole weight of the pier was hung by cables that ran from winches below up over the top of each spud leg. The Diesel electric winches in the 'tween decks of the pier, where the winches took the strain, were the means of elevating or lowering the piers to adjust them to the rise and fall of the tide. Here in the 'tween deck not only was there machinery space for the winches and cable drums, but also living quarters for the crew who would operate the structure.

By hoisting on the winches as the tide came in, the piers could be raised so as to be semi-floating, with part of the weight resting on the spud ends of the legs. Under this weight the spuds dug down into the bottom muck, acting as anchors. The four legs dug in, steadied the structure and kept the deck level. The surface of the pier was thus always firm, never tilting or wobbling.

Since the men on watch at the winches could hoist and lower with the tide, the Lobnitz pier was always at a uniform height above the water for maximum ease of unloading. If the piers did not have this elevator-like characteristic of raising and lowering, at low tide they would be twenty feet above the vessel that was alongside to be unloaded, which would halt operations.

Another design problem that had to be met in the three half-mile Whale roadways leading out to the Lobnitz spud piers was the obvious sideways thrust and bend they might take from the wind and current. To offset this, it was necessary to anchor each pontoon with a thousand-foot wire rope cable and anchor.

All this elaborate structure of floating Whale roadway  p69 and Lobnitz piers would quickly be wrecked in rough weather and breaking seas, to say nothing of the heaving of the roadway, if exposed to the open sea. This led back to the even more fundamental and basic problem of all Mulberry planning, providing calm water.

To provide sheltered water, a breakwater made from a line of concrete cellular caissons, called Phoenix units as has been said, was planned. They would be towed individually to the site, then sunk in a line, butt to butt, following the contour of the five-fathom depth curve.

These caisson monsters were of five different sizes, ranging from A‑1 units of 204‑foot length to C‑1 units 176 feet long. This Phoenix breakwater was thought of as having three openings. An entrance gap to the west was provided, protected by a side arm breakwater. Another opening was planned for the east around the other end. A 200‑foot opening was laid out at the center as an additional inlet for traffic. Forty-seven huge Phoenix units were required to build this sixty-foot-high breakwater wall at Mulberry A. Nineteen spares were provided as some loss from enemy action while in tow was anticipated.

This breakwater would provide sheltered water for the pierheads and roadways. In addition to the ships berthed at the Lobnitz piers, there would be theoretical space for mooring seven Liberty ships or large coasters inside the Phoenix shelter. These ships would be served by overside discharge into duckws,​2 barges, Rhino ferries​3 and landing craft.

 p70  Since the enclosed stretches of the beach itself would be freed from breaking seas, other landing craft could by‑pass the piers and go direct to the beach, giving still further discharge capacity. Smooth water would be vital for this, since breaking seas at a beach make even sea‑kindly craft unmanageable, to say nothing of blunt-nosed landing craft without keels and with inexperienced coxswains steering.

The concrete Phoenix breakwater really stood at the heart of the Mulberry plan, which let men for the first time in military history dare to chance the weather and invade over an open beach.

But more than just making the giant caissons had to be provided for.

The towing of each caisson was admittedly a major operation. Because of the burden of towing, it was at first forecast that at least fourteen days would be required to complete the Phoenix tows alone, even with the mobilization of tugs from all over the world. There still remained the other Mulberry elements requiring towing after the breakwater units were taken care of.

To cope with the problem of earlier shelter, in shoaler water to the east an additional breakwater was to be created. For this, a 9,000‑foot line of old merchant ships was to be sunk end to end. This was known by the code word "Gooseberry." The extension of the harbor thus formed gave almost as long a shelter as the Phoenix-enclosed portion, and presumably much earlier, but with water less deep inside. It could serve smaller coasters which could dry out​4 and landing craft. This line of sunken ships had to be placed  p71 quite far in toward the shore since the 21‑foot tide of high water would otherwise wash over their hulls and nullify the protection. It would serve principally as shelter for landing craft.

Even the large total harbor area thus created by both Phoenix and Gooseberry would hold only an emergency fraction of the ships in the area for unloading. Hence a third breakwater even farther out was considered. Here the water was too deep to sink caissons or ships. This was to be therefore a floating breakwater. It was believed that some type of floating units could be devised which when anchored in line would dampen the wave action inside. For this many bizarre schemes were considered. Long inflatable canvas tubes with reinforced concrete keels, rows of perforated pipe to spray compressed air upward, triangular concrete floating caissons, a row of moored ships — all these and many more fantastic ideas were considered.

Finally a hollow steel cruciform structure proposed by Robert Lochner was adopted. These objects floated two‑thirds submerged. They were called Bombardons — and were two hundred feet long. From the narrow central shape steel fins protruded underwater nine feet on each side, clumsy and murderous-looking to a sailorman. To come alongside this underwater fin for handling or towing would be really difficult. Nevertheless after tests they did seem to have a smoothing effect on the water and the Bombardon scheme was duly adopted. Like their code name, they looked like gigantic battering rams. Twenty-four of these were to be moored in a long row outside the breakwater of Phoenix caissons and the Gooseberry sunken ships.

 p72  In spite of these elaborations, the Phoenix units were at the heart of the whole Mulberry scheme. Yet of all the structural elements required for Mulberry, with its vast requirements of steel and cement and labor, the Phoenix caisson units were the first and most outstanding construction problem.

Forms for some were set up in the sorely needed Royal Naval Dockyards at Stokes Bay, still others as far away as East India docks in London. Some were built part way up, inland, then launched by digging a channel in to them. The structures were then finally completed afloat. In all, some twenty-eight construction sites along the south coast of England within reasonable reach of deep water were selected and a week-by‑week construction schedule adopted.

By 31 October, 1943, work was commenced. As early as January, it was clear that all the Phoenix caissons would not be finished in time for the invasion, much less with time to train crews to man them. Construction was already three weeks behind.

The U. S. Naval side — at this time ComNavEu's Logistics Section — could only try to pry out the actual facts of construction progress. It seemed imperative to get an experienced U. S. construction engineer on the spot to check on the program. There was a mounting suspicion that optimistic British progress reports were based on wishful thinking. Capt. C. R. Johnson, CEC,​5 USN, was rushed to England to investigate the situation and give a realistic appraisal of the chances for completion.

A grim meeting held after Captain Johnson's arrival listed  p73 these problems in connection with Mulberry in the face of firm optimism from the British side:​6

a) labor not yet half recruited

b) work at majority of Phoenix sites not begun

c) space to store finished caissons nowhere available in U. K. All harbor space allocated

d) no moorings available or provided for launched units

e) no pumping gear

f) no space for crew's living quarters.

In addition to worry over whether the specifications provided sufficient strength for floors and the partitions of the ten watertight compartments, Captain Johnson was concerned about the stability of the caissons when partly sunk — i.e., whether they would roll over. Despite tests at the National Physics Laboratory at Teddington, with models, there was no experience on caissons of this huge size. In sinking them, extremely well-timed co‑ordinated handling of the eleven scuttling valves would be required. It could be readily seen that unless control was quick, should a list to one side or the other develop, the water would rush to the low side and capsize the structure.

Plainly there was urgent need for at least one completed full-size Phoenix structure at the earliest possible moment.

Lack of iron reinforcing rods was a constantly plaguing material problem in completing even the first units. The labor problem had been seen as an almost impossible requirement, particularly when one realized that from the outset pouring the huge volume of concrete was actually to be  p74 undertaken by hand hoist, bucket by bucket. Some of these buckets were so small they held only one‑third of a cubic yard of concrete. This slow method magnified the amount of labor required. Low diet and the weakened condition of the men available were never properly allowed for in establishing the progress schedule.

Instead of early January or December, actually it was 27 February, 1944, before the first towering unit reached the full height of 60 feet in the London docks. There, over a frail scaffolding and broken ladders, a few of ComNavEu's senior officers were persuaded to clamber up. Looking down into the caissons from a warped and teetering plank laid across the partitions, one could, however, truly comprehend the size of these strange objects. Reach rods leading to the eleven scuttling valves in the bottom disappeared downward into the murky, almost unseeable, depths from the dizzy height of the top of the structure.

Until the end of the enterprise these Phoenix caissons were the cause of continuing difficulty and delay.

At Stokes Bay one of the early units collapsed, causing numerous casualties and creating a delay of six weeks in completing other units at the site. Others developed cracks and strains.

In February, 1944, the tight knot of dedicated men in Number Eight Grosvenor Square was still in London, still without an adequate skeleton force of officers and men to meet assigned responsibilities, without any experience in towing, sinking or handling at sea the concrete monsters that were the basis of Mulberry.

Until actual towing tests were possible, tug requirements could not be estimated, except in generalizations by British  p75 civilian towing experts. Of these Captain Mylchreest was surely one of the best informed and most experienced. His guesses figured that two sea tugs of 2,000 hp. would be required for each Phoenix unit. There was a total of 149 Phoenix units required for both U. S. and British Mulberries. That would mean a lot of tugs must be found for the seven and a half miles of Whale bridging, twenty Lobnitz piers for the two harbors and forty-eight Bombardons. Plainly this indicated a larger number of tugs than there probably were in the entire Atlantic and Pacific. No one dared really calculate how many hundred.

The British in meetings held that the U. S. could supply tugs, but all the U. S. sea tugs might not exceed 150 and there were other duties for them. The British argued that handling the heavy shipping for the build‑up in British tidal harbors would permit the release of only a small number of British tugs to Mulberry duty.

In Washington, the Navy Department stood flatly by its original commitment, expressed in the first Joint Chiefs of Staff paper that offered twenty-five "U. S. towing vessels" for Mulberry. Towing and salvage commitments in the Pacific with its immense area and distances made further U. S. tug allocation impossible.

Unfortunately of the twenty-five "towing vessels" in the U. S. commitment, it turned out that eleven were YMS's. A YMS was a small, wooden, harbor minesweeper, utterly unsuited to a heavy tow in spite of its 1,500‑horsepower engines. There were not even bitts aft that could hold a towing bridle. To all practical purposes the YMS's assigned were so many high-powered motor boats.

Finally no decisive action could be precipitated as to any  p76 assembly area where the Phoenix units could be moved until their dispatch to the Far Shore on D‑day. All the south coast harbors of England would be filled to their limit with landing craft, transports and cargo vessels in the assembly period.

With Phoenix units of doubtful stability and floating characteristics, hopelessly behind in construction schedule, no personnel to man them, a bare handful of tugs to tow them, and no place to store them, Force Mulberry knew it had a problem for which there was only the remotest reasonable hope of partial resolution.

It was hard to meet army officers who had seen the model of the harbor in the secret room in Forty-seven Grosvenor Square, look them in the eye, and agree with them that Mulberry was indeed a wonder­ful project and that their landing and supply behind Mulberry's safe walls were assured by skilled naval planning.

What could one do or say at such a point, except to go back to the dark chill rooms of Number Eight and once more comb progress reports in hope of more promising construction news; again screen signals one by one in hope of finding a new tug; and thumb over and over again the cards that listed available naval personnel in the U. K. and personnel supposedly en route.

After this there was the map of the Channel and beach area, full wall height. One's eyes dwelt long on the shoreline of that open beach below Colleville and St. Laurent. A loaded duckw had only a bare foot of freeboard above the water. Landing craft pushed at any speed in rough weather would ship water heavily.

In the mind's eye it was easy to see how a mild blow from  p77 the north or northeast could quickly produce a sea on that beach, and make it virtually unworkable. Mulberry had to be there.

Some unpleasant facts, obviously, had to be faced soon. The months left before the invasion date, vaguely assumed to be about 1 May, 1944, were slipping by with dangerous rapidity as February neared its end.

The calendar at last began to threaten in a way meetings and promises could not dispel.

The Author's Notes:

1 Presumed to have been so named for their designer and manufacturer in Scotland.

Thayer's Note: Henry Pearson Lobnitz, managing director of the family firm Lobnitz & Co Ltd, of Renfrew. For the piers themselves, see the page at the University of Glasgow (with several photographs); for the company and its founder Henry Christian Lobnitz, its page at Archives Hub.
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2 Amphibious truck. Could carry one and a half tons in smooth water.

Thayer's Note: Usually written DUKW (an acronym, though pronounced "duck").
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3 Broad steel barge, powered with outboard motor.

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4 I.e., remain high and dry as the tide went out.

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5 Civil Engineer Corps.

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6 Expressed repeatedly by Brig. Bruce White, British War Office head of the project and friend of the Prime Minister.

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