Roiling the ocean into a quarter-mile of froth, a gray and barnacle-encrusted snout reared up through the surface of a darkened sea, gave voice to an “awesome, frightening, ear splitting” roar, and spewed a geyser of spray more than 50 feet into the air. Briefly the monster shape strained at the lines which tethered it, as if fighting back at the ships which had just brought it up from the deep. Then gradually the venting subsided and the huge form settled down in apparent surrender to its captors. Divers dropped into rubber boats and paddled cautiously to the motionless hulk, then clambered up onto the unresisting skin. It was the evening of 12 July 1964, and the crew of the USS Windlass (ARSD-4) had finally brought an end to the saga of one of the most ornery beasts ever encountered by the U. S. Navy.
Few Navy men had heard of the XMAP and even fewer had laid eyes on the monster during the eight years of its existence. Its characteristics were a well- kept secret, because it was a device intended to sweep the notorious pressure mine. In appearance it was a cylinder 250 feet long and about 19 feet in diameter that lay nearly awash in the water with a few mysterious-looking protuberances attached to its outer skin. Its genesis resulted from World War II.
Of all the diabolical anti-shipping devices contrived by the ingenious scientists of the Axis countries, the German pressure mine was probably the worst— almost impossible to sweep safely. The only thing that could produce a pressure signal that the mine would recognize was a good-sized ship, which was intended to be the mine’s victim in the first place. A reasonably effective solution to the problem was improvised for such tasks as clearing U. S. pressure mines from the waters around Japan. Several war- damaged ships of little remaining value were fitted with remote controls for the critical items of machinery, packed with flotation cells not unlike ping-pong balls, manned by skeleton crews stationed in a well-padded control room in the highest part of the ship, and sailed brazenly through the mined waters.
In the years after the war, the Navy devoted considerable effort toward finding more sophisticated methods of countering the pressure mine. In the early 1950s, three Liberty ships—the former Floyd IV. Spencer (YAG-36), John L. Sullivan (YAG-37), and Edward Kavanagh (YAG-38)—were filled with refined versions of ping-pong balls and remote controls. Probably the most original of these was the YAG-37, which was fitted with a propulsion plant consisting of four surplus T-54 turboprop airplane engines mounted on the main deck, thus eliminating boilers, gearing, shafts, and propellers as candidates for derangement.
In addition, the Navy had picked up the idea of designing a truly indestructible sweeping device based on a 1944 proposal by the David Taylor Model Basin personnel. The concept was that of a huge cylindrical hull, roughly the size and shape of a submarine, but made of what was essentially steel armor plate. The only problem was that the technology for welding plates of this thickness did not exist. (The armor plates of battleships were keyed together and bolted to the hull. It would be impossible to make a self-supporting, watertight hull using this technique.) By 1949, however, the Navy thought that the requisite welding procedures could be developed, and the design of the proposed device was undertaken.
The plans which resulted called for a cylinder 251 feet long with a maximum diameter of 281/2 feet, tapering to blunt ellipsoidal ends. It was to be made of special nickel-chromium alloy steel of the highest quality, forged and heat treated, and rolled into plates varying from 3!/> to 10!A inches in thickness. The displacement of the finished hull was 2,880 tons, and 2,626 linear feet of welds were required to join its plates together. There could be no notches in the surface, and distortion during construction and welding had to be held to a minimum, for “the plating will be stressed up to its yield point from loads induced by shock, blast, and longitudinal bending,” in the words of the Navy’s specifications. Under such circumstances, notches and similar discontinuities are notorious “stress raisers” or points where cracks can start and propagate to the extent of complete failure of a hull.
To make welds of the type contemplated, men had to be specially trained, tested, and qualified before being allowed to touch arc to steel. The plates had to be precisely beveled to produce a double V groove welded from the center outward on both sides, preheated to 200° F., and clad on both edges with two layers of weld metal before the main production welding sequence could begin. Each weld bead was to be wire-brushed, inspected, and peened to cause deep mechanical working in order to relieve any stresses that might be “locked into” the structure. During production the plates had to be kept heated between 100° and 300° F., and each layer or pass had to be proven free of cracks by magnetic particle inspection. Any unsound metal had to be chipped or gouged out and rewelded. The entire procedure would involve tons and tons of welding rod deposited in bead after bead, layer upon layer, requiring many man-years of continuous welding during which the steel could not be allowed to cool.
Funds for two of these massive devices were included in the naval construction program for fiscal year 1950. The reason for planning a pair was that they were intended to be towed in tandem through a real or suspected minefield, sweeping a path wide enough to make a usable ship channel in a single pass. The two units were to be linked by struts with ball-and- socket joints at each end and towed with a bridle arrangement by a tug far ahead. The nomenclature XMAP was assigned to the devices, standing roughly for “experimental magnetic, acoustic, and pressure” minesweeping device. The construction of XMAP-1 was assigned to the Philadelphia Naval Shipyard, but so difficult were the technological problems involved that delay after delay resulted and costs soared far beyond original estimates. Before long it became apparent that XMAP-2 could never be built, and the authorization for its construction was cancelled in 1954.
In the meantime, the Navy procured a less expensive stand-in in the form of a cylindrical vessel of identical external dimensions but built of ordinary 30.6- pound steel plate which could be fabricated by conventional methods. This tank, designated EC (for experimental caisson) would be ballasted down with five feet of solid concrete to have the same draft as the genuine XMAP. Although it would not be capable of surviving a mine blast, it could be towed to test the feasibility of handling the devices at sea. Two of these so-called caissons, EC-1 and EC-2, were ordered from the Tampa Ship Repair and Drydock Company under the fiscal year 1952 shipbuilding program.
When the XMAP-1 was finally completed, it resembled a belly-up whale on which had been mounted a pair of huge coils of copper wire, referred to as the “dog blanket,” towing and mooring pads, portable spars for the legally required running lights, and a minimal access platform. For the initial towing tests, the Navy contracted with the experienced Moran Towing and Transportation Company, which assigned Captain Ira F. George and the tug Marion Moran (a | former Navy auxiliary tug) to the job. On 20 March 1956, they departed from Philadelphia with the XMAP-1 and arrived at Panama City, Florida, eight days later, having achieved the respectable speed of advance of eight and one-half knots. Captain George’s report stated that “this device does not pose any difficult problems, based on ordinary towing standards.” For the next two months he conducted further tests with various types of towing rigs, finally concluding that the best setup was a three-legged bridle with a shorter middle line to take the normal towing strain and two outer spans to pull the tow back into line if it should start to veer to either side.
Handling the XMAP in restricted waters, as in entering and leaving port, was quite another matter. The tremendous inertia of the almost-submerged cylinder made it extremely difficult to control through a narrow or crooked ship channel, and it is reported that the XMAP proved to be a very efficient sweeper of navigation buoys. Captain George pointed out in his report that the towing vessel could easily be “tripped” by the tow when making a turn, and appended a little diagram showing the juggernaut “taking charge” and dragging the hapless tug around by the stem. To avoid so ( embarrassing a situation, the captain recommended a rig for towing alongside such that the tension of the different towlines would always keep the beast under control.
All in all, the problem of towing the XMAP proved to be quite manageable. Even in tandem with one of the ECs, catamaran style at the end of 1,200 feet ot 2-inch plow steel towing wire, she was reported to make a “good handling tow.” The results of the minesweeping experiments remain locked in the classified files, but on completion of the tests the XMAP was tied up at the Mine Defense Laboratory in Panama City.
Months passed, then in March 1961, the naval architects working on the design of the America (CVA-66) needed data on “bubble pulse” loading. Someone remembered the XMAP, and the Chief of Naval Operations authorized that it be used for explosive tests and disposed of when they were completed. Six blasts were set off without incident, but on the seventh an 1,800-pound charge of high explosive tore off the starboard skeg and opened a crack about 8 feet long and, at most, half an inch wide. As the tugs labored vainly to get the sluggish XMAP back to port, she slowly filled until her stem dragged bottom in about 150 feet of water. Two days later, on 23 November 1961, she gurgled to the bottom off Panama City.
Within a few days, the submarine rescue vessel Penguin (ASR-12) arrived at the scene, sent down divers, and rigged an old battleship mooring buoy to the sunken hulk. Then the divers connected an air hose to a 1-inch access pipe on the XMAP’s deck, and for two days the Penguin pumped compressed air into the big cylinder at 175 pounds per square inch until bubbles could be seen coming out of the crack. Still the XMAP never stirred in her resting place. The rescue vessel fixed a towline to the mooring buoy and hauled away in hopes of breaking the bottom suction, but no amount of heaving would start the waterlogged hulk toward the surface. Plagued with repeated breakdowns in the air compressors and faced with worsening weather, the Penguin's divers went down again, only to find that the crack was longer than previously believed. The decision was made to discontinue operations, flood the hulk, and sink the marker buoy lest it menace navigation. On 1 December 1961, the XMAP was flooded and abandoned.
Two and a half years elapsed before the Bureau of Ships initiated another attempt to raise the sunken XMAP. This time the task was assigned to Service Squadron Eight and the Norfolk-based Windlass (ARSD-4), a former medium landing ship, converted to a salvage ship and fitted with heavy lifting horns extending out from the bow. Norfolk Naval Shipyard prepared an engineering analysis and stability estimate, extra divers were detailed to the ship, and personnel familiar with the XMAP, including the former commanding officer of the Penguin, were consulted. Then the salvage crew moved to Key West for the big effort.
When all was in readiness, the Windlass and the minesweeper Bittern (MSC-43) departed on 6 July 1964 for the scene of the sinking. There the minesweeper soon located the massive steel body and dropped a marker right on the XMAP’s deck. For the next four days, salvage divers and underwater welders fitted blow and spill connections to the XMAP's manholes and the Windlass began pumping air. By the 11th, the air bubble reached the crack, whereupon the salvagers fashioned lead wedges and drove them into the crack. On the following evening, without warning, the stem of the XMAP surfaced with the sound effects previously described. When daylight came, welders went over and closed as much of the crack as possible, and all would have been ready for the final blow had not the weather worsened. The wind and seas rose until the Windlass rolled up to 40 degrees in the trough of the waves, compressors broke down, and the little yard tugs that were assisting in the operation had to cast off from the derelict.
On 16 July the weather appeared to be moderating, so the Windlass again made fast to the XMAP and had started to replace the salvage gear when a line of squalls came howling down from the northeast at 40 knots. Within a few minutes the tug Salinan (ATF-161), which was anchored with a hawser holding the port quarter of the Windlass away from the upended XMAP, dragged anchor and drifted across the salvage ship’s bow. The hawser had to be cut, whereupon the Windlass swung helplessly down on the XMAP. To the surprise and relief of all concerned, the deep-lying hulk set up a roll of water which effectively acted as a fender between the two vessels, and their hulls merely kissed lightly and harmlessly. Three more times that night squall lines passed over the little flotilla without further mishap, and with the dawn all was made secure. Heavy weather continued until the 21st, and the ships used the enforced lull in their salvage work to replenish stores at Key West. Then the tilted XMAP was once again hauled close in between the bow horns of the Windlass, and a final welding pass was made to seal the troublesome crack. Blowing was resumed.
As the air compressors pounded away, at 0125 on the morning of 22 July the XMAP suddenly rolled slightly to port, started “walking” along the bottom toward the salvage ship, then rose gently to the surface in a sea of froth and gave vent to a final five-minute geyser of air and water before subsiding into inertness. The salvors retrieved their gear and cleared away the accumulated debris. The tug Luiseno (ATF-156), which had relieved the Salinan that morning, passed a towline forward while the YTM-543 acted as a drag astern, and the triumphant task group set off for Key West, mission accomplished.
The remains of the XMAP were sold for $96,000 “as is, where is” on 25 August 1964 to a scrap buyer, after the copper “dog blanket” coils had been stripped off by the Navy. The salvage operation had cost only $7,300, exclusive of personnel time, which was considered well spent as a realistic training exercise.
