The campaign that finally cracked the Nazi “Fortress Europe” in World War II was spearheaded by the daring Allied landings on the bleak, exposed coast of Normandy in June, 1944. Because there were no harbors, the Allies had to make them. They sank old ships to form breakwaters, and within these artificial harbor areas built unloading platforms which were linked with the distant shore by long pontoon causeways. The code name for these makeshift port facilities was “Mulberry.”
But a vicious storm almost completely wrecked these fragile links in the chain of supplies so desperately needed by the troops just put ashore, and for a time disaster threatened. Fortunately the sea calmed and repairs were made in nick of time.
Engineers who studied the “Mulberry” experiment decided that, for future landings on an open coast, some less vulnerable apparatus would be necessary. For, despite the rapid development of freight airlifts, helicopters, etc., ships and docks remain the surest and most efficient means of moving large quantities of heavy equipment and cargo from a task force or a supply fleet to a beachhead.
But good docks are hard to build, and particularly under enemy fire. Even the “Mulberries” required eleven days to two weeks to construct, and because they had floating pierheads and causeways, they were always at the the mercy of wind and wave.
A possible answer to the problem has recently been undergoing rigorous military tests. It is a combination barge-pier unit called the DeLong Dock. Like many another military weapon or accessory, it was originally designed for civilian use. After a series of trials under various climatic and other conditions, the Defense Department, at the recommendation of the Corps of Engineers and the Transportation Corps, U. S. Army, has decided to order eleven of them. Five units have been put into use, and the other six will be employed in training.
The DeLong Dock is similar to the “Whale,” code name for the floating pierheads used in the D-Day “Mulberries,” in that it is basically a barge with steel legs that rest on or penetrate into the bottom. There most resemblance ends. The “Whale” rose and fell with the tide, and had the vulnerability of a ship in a heavy storm. Its steel legs were comparatively fragile, and there were far too few of them to keep the barge-dock firmly in position. It was at best a hasty expedient, with no permanent value as a dock.
The DeLong Dock, on the other hand, can be used either as a temporary or a permanent installation, hence its value in peace as well as war. Because it is prefabricated from standard steel stock, the basic barge (which becomes a dock platform) can be built in any shipyard. It can be towed thousands of miles in rough sea, carrying on its deck all the equipment and parts needed for installation, including its pier-like legs, a crane for assembly, and the powerful airjacks with which it can lift itself from the surface of the water, above the damaging effect of storm waves.
Mr. Leon B. DeLong, developer of this new device, and a construction contractor for many years, noted the need for stout but mobile pier installations in the Gulf of Mexico, where portable platforms were used in off-shore drilling for oil. In order that they should not be too expensive, these rigs must be capable of being quickly dismantled when a well is brought in, or when the operation proves to be a dud, so that the equipment may be used elsewhere.
It seemed obvious that some kind of “a barge on stilts” was needed, but the big question was how to raise or lower a platform heavy enough to stand the weight of drilling equipment and the shock of drilling operations; also a setup sturdy enough to cope with an occasional hurricane.
The solution to the weight-lifting problem was found in a new and revolutionary kind of gripper-airjack, a powerful gadget that almost literally allows the barge-dock to raise or lower itself by its own bootstraps! The operation can be compared to a boy shinnying up a pole, and is so simple that the first reaction to seeing it work is: “Why hadn’t anyone thought of this before?”
Each dock thus far has been tailor-made to meet specified conditions, consequently the barge units exist in several different sizes. But they could easily be standardized, and they could be built or assembled in any moderately well-equipped shipyard. Consolidated Western Steel Company, at Orange, Texas, did the first ones.
The welded steel barge itself has proved most seaworthy, even with heavy deckloads. Thus far these “package docks” have been towed, with all their gear packed on deck, not only to oil-drilling sites in the Gulf of Mexico, but also to locations in South America, Alaska, and Greenland. One of them is used for a full-scale training unit at the great Army Engineer’s base, Fort Belvoir, on the Potomac below Washington.
It was here that I had a chance to see how the airjack-gripper really works. The training dock at Tompkins Basin, Belvoir, measures 250X60X10 feet and weighs 850 tons. When afloat it draws only about 3 feet of water. This shallow draft permits it to approach very close to the shore. The demonstration unit has caissons or piers in all stages of erection, from lying flat on the deck, to upright but not lowered, and lowered. Air- jacks are shown in operation, half dismantled and completely removed. A crew of two officers and eight enlisted men put the big dock through its paces.
First a big mobile (tractor) crane, which is carried on the barge deck to location, swings one of the caissons on deck into a vertical position. There are twelve of these huge caissons, which serve as legs or piers, to each barge of this size. Actually they are great welded tubes of ¾" steel, six feet in diameter and 100 feet long. Each caisson is carefully lowered into one of the holes in the deck. The holes go clear through the barge, a series of wells along each side of the deck. If the barge is in the place desired for a dock, the caissons are lowered until they touch the bottom.
When all of the caissons have been placed, one at a time, by the crane, the airjack-grippers, which fit like a collar around the caisson at the top of the deck well, go to work. The jacks have two parts, each being a heavy steel ring or jacket, lined with rubber gripping surfaces capable of holding the caisson tightly at any point. Between these bands lie two sets of heavy rubber bellows- tubes which are alternately inflated and deflated. At the same time, either the upper or the lower grippers are tightened or released (by compressed air), depending upon whether the caisson is to be raised or lowered.
It is this alternate grasping and releasing, plus the expanding tube action six inches at a time, that pulls the pier up or forces the caisson down into the mud of the bottom— all very much like a boy “shinnying” up a tree. The jack uses the weight of the pier to drive the caisson deeper into the bottom, or its flotability to pull it out, all without the use of the crane.
If a permanent installation is desired, however, a steam hammer, lowered from the crane, is employed to drive the caisson home. Shear lugs then fix the caisson to the barge, the airjacks are removed, the caisson top is cut off flush with the deck, and capped with a steel cover. You then have a smooth, unbroken dock that quickly can be adapted to any purpose, even to the carrying of railroad tracks, or the erection of a conveyor tower to link the dock with shore. All of the airjacks can be operated simultaneously from a central control panel to lift or lower the barge on its caisson legs, but each jack may also be run independently, for final levelling—a mere 1/32" if necessary!
For military purposes, the DeLong pier has three advantages: (1) Its mobility—it can be taken right along in the wake of a task force to any part of the world; (2) speed of erection—a few days, instead of weeks or months for other fixed-type decks; (3) Reuse—it can be removed in good condition as quickly as it was set up, and placed elsewhere an almost indefinite number of times. In addition, the barge itself can be a cargo carrier, a convenience in salvaging valuable military equipment “to fight another day” if a sudden evacuation is ordered.
One of the principal civilian installations of the DeLong Dock has been at work for the Orinoco Mining Company, a subsidiary of the U. S. Steel Corporation, since 1952. This terminal for loading iron ore from the famous Cerro Bolivar mountain, is at Puerto Ordaz, Venezuela, 180 miles up the Orinoco River. Specifications called for a dock rugged enough to handle iron ore for many years, and strong enough to support large ore-handling conveyors, as well as two moving transfer towers, each weighing 900 tons. Another consideration was that the Orinoco at this point is subject to floods that raised the river level 40 feet above normal. This dock, 82 feet wide and 1,130 feet long, was constructed in three sections at Consolidated Western Steel, Orange, Texas, and towed to the site, carrying as deck cargo not only all its own equipment, but also launches, motor trucks, 13 railroad cars and two 180- ton diesel locomotives.
An earlier DeLong pier was installed under entirely different conditions. More than a year before the first released news of the new airbase at Thule, Greenland, four dock sections each 50X250 feet, were fabricated in Houston and Galveston, Texas, and towed by Navy tugs 4,800 miles to the site. Less than two weeks after their arrival, materiel and equipment of all kinds were being unloaded directly from transports and supply ships to trucks on the docks and hauled ashore. Utmost speed is necessary here because Thule is open to navigation only two months of the year.
Two units recently were installed at Whittier, Alaska, to replace a wooden pier destroyed by fire. The shoreline here falls off steeply into deep water, so the docks were placed parallel to the water’s edge. The caisson legs on one side of the barges go down a considerable depth, on the other side only a few' feet. Because of the rocky bottom, almost all the legs are of different length, yet the dock sits firmly and handles cargo more efficiently than the previous wooden dock.
Numerous uses other than those cited above have been proposed for this ingenious device, including placement as temporary piers for seasonal tourist traffic. Many West Indian islands, for instance, now have open roadsteads and cannot be visited by winter cruise liners. Other northern resorts have the same situation, and are not touched by summer cruises. The same barge docks could be used for each. Another application, where shoals prevent ships from approaching the shore, is as an offshore “island, with cable- ways carrying passengers or freight for transfer to ships. This phase is undergoing engineering tests at Fort Eustis, Va.
What other jobs the barge-dock can do remains for time and circumstance to prescribe. It requires little play of the imagination to visualize their possible usefulness as helicopter supply bases for Arctic, Antarctic or jungle exploration, or as permanent advance weather or sonar or radar stations, or as fishing vessel depots on remote ocean shoals, or even as platforms for launching guided missiles.