Wonsan: The Battle Of The Mines*

On the second floor of the capitol in Seoul on September 29, 1950, General MacArthur met with his subordinate commanders and described how he planned to end the Korean War with another amphibious envelopment. In just three weeks, on October 20, the Tenth Corps would land at Wonsan. While this end-run was taking place, the Eighth Army would push directly toward the North Korean capital of Pyongyang and the ROK’s would drive north along the east coast. Later the same afternoon, Major General Edward M. Almond, USA, the Tenth Corps commander, began the implementation of the Wonsan plan and stated that he hoped it would be possible to make the landing by October 15.

During these early days of planning, the critical threat to be presented by Communist mines and the significant role to be assigned United Nations minesweeping forces were by no means clearly foreseen. Within two weeks, however, the Wonsan landing operation could justly be called, “The Battle of the Mines.”

Historical Background of the Communist Mining Campaign

Before commencing the narrative of the problems encountered by the U. S. Navy’s minesweepers at Wonsan, it will help the reader’s understanding if the Russian interest in mine warfare is documented and a brief description is given of the hydrography of Korea.

Historically, Russia has long been noted for her interest and success in mining. She used the mine effectively in the Crimean War, in the Russo-Turkish War of 1877 and ’78, and in the Russo-Japanese War of 1904 and 1905. In the latter conflict, for example, the Soviet Navy sank two Japanese battleships outside Port Arthur in a single day with moored contact-type mines of a type very similar to those that were to be used so effectively at Wonsan nearly a half century later.¹

Initially, the Soviet mining effort in North Korea was probably undertaken to keep UN ships out of North Korean harbors and to limit UN naval offensive capabilities. As it turned out, Korea provided the Soviet Navy an ideal opportunity to test the U. S. Navy’s ability to cope with mines in the western Pacific as of 1950. At the same time, Soviet Russia was able to help her North Korean satellite delay the advance of the UN ground forces.

The Korean peninsula was almost ideally suited for an experiment in defensive mine warfare. First of all, much of the Korean coastal area was shallow—ideal for minefields. Second, the muddy waters offered near-perfect concealment. Third, ocean currents in both the Sea of Japan and the

Yellow Sea were such that floating mines, easily launched from the many junks and sampans, would traverse the entire length of the peninsula within fifteen days. In such a favorable area the Soviets could once again make full use of mines to forestall further amphibious assaults by planting minefields off every suitable beach area and to make coastal bombardments hazardous by the use of offshore moored minefields.

The Modern Mine

Mines have been employed in naval warfare for more than 350 years. Until about 1880, sea mines were known as “torpedoes.” Admiral Farragut’s famous order at Mobile Bay, “Damn the torpedoes, Four bells!” was made in regard to the crude sea mines built and used by Confederate forces during the Civil War.

Until the advent of World War I, the sea mine was a simple but effective weapon. A large charge of gunpowder or TNT, encased in a suitable container, was chained to the floor of the ocean by an anchor so that the mine itself bobbed beneath the surface some ten to twenty feet. Several triggering “horns” protruded from the mine container. If a passing ship made contact with one of these horns, the mine’s firing circuit was closed and the mine exploded—usually with fatal consequences to the contacting ship. These mines are cut by streaming sweep cables from the stern of the sweeper with “depressors” and “otters” to hold the cable—with cutting gear attached—at proper depth as well as to force the cutting cable to plane outboard of the sweep vessel. Floats or “pigs” keep the cable from running too deep.

Commencing with World War I, however, this simple type of contact mine was joined by the first of several other types. The British at that time developed and used the first magnetic mines.

In World War II, still more treacherous mines were developed. It was no longer necessary for the ship to strike a mine. Modern mines could be detonated not only by the shifting lines of force of the earth’s magnetic field as a ship’s steel hull passed near it, but also by the noise of a ship’s propeller, or by the reduction of water pressure caused by a passing ship’s hull, or by a combination of these influences.

To sweep the modern magnetic mine, which was perfected by the Germans in World War II, minesweepers must duplicate the influence to which the mine itself responds. The magnetic sweep gear consists of two large cables—a short “leg” and a long “leg”; these are lowered into the sea from the minesweeper’s stern. Floats known as “pigs” keep the cables buoyant. The long leg is allowed to drift astern of the sweeping vessel some 1,200 feet distant. At the end of each leg is a copper electrode. When the electrical cables are in position, a powerful generator aboard the sweeping vessel is turned on. This transmits a powerfully pulsed current which passes through either a closed loop of cable or through the cables and a water path between their electrodes kept safely astern of the sweeper. Thus, a strong magnetic field is created, capable of detonating magnetic mines within the cables’ influence.

The second type of modern mine is the acoustic mine—which can be detonated by the machinery or propeller noise of a passing ship. Like the magnetic mine, it can also be planted on the floor of the sea. The acoustic mine utilizes a simple hydrophone or an “artificial ear” that is set to “hear” a ship’s engines or propellers. When it does, its diaphragm vibrates and closes the fatal switch. Acoustic mines are destroyed by duplicating the noise of a ship’s propeller. The equipment for doing so is called a “hammer” or a “bumblebee” that rumbles as it is dragged through the water.

The third type of modern mine is the pressure mine. In the evil lexicon of mine warfare, pressure mines are even more unsweepable and diabolical than either acoustic or magnetic mines. In a pressure mine, the negative pressure of a passing ship sucks a diaphragm upward, closing the firing switch. Consequently, to sweep them, the minesweeper must endeavor to duplicate the change in water pressure produced by a passing ship. This requires that either an underwater hull like that of a ship, in both size and shape—called a “guinea pig” ship—be pulled through the minefield or some other means be employed to induce the same kind of pressure change in the water.

Fourthly, the toughest type of modern mine is the combination mine—one that combines one or more of the above types in the same carcass—a magnetic-acoustic, or a pressure-magnetic mine. This type will only explode when the sweepers employ two or more of the disturbing forces. To make the problem even more complicated, “ship counters” can be built into the firing circuit of nearly any type mine. These counters can be pre-set so they will explode only after five, ten, or more ships have passed safely by. The minesweeper can thus sweep a channel a predetermined number of times, declare the channel “clear,” and have a mine explode beneath the next passing ship.

These are the main types of modern mines which naval science had devised at the time of the Wonsan landing. They are passive weapons which complement other naval weapons in controlling the seas. They can deny access to harbors, approaches, and ocean areas where the water depth will permit, to friend and foe alike.

Retrenchment Hits Mine Warfare in U. S. Navy After World War II

The attitude in the U. S. Navy toward mine warfare, generally until October, 1950, and occasionally since, has not been unlike the bitter sentiment against mines expressed in 1805 by the British Admiral, Earl St. Vincent, to Prime Minister William Pitt. The latter had given encouragement to Robert Fulton to build a mine from a gunpowder keg. “Why should we who depend utterly on command of the sea,” said the British Admiral, “seek to develop a weapon which we do not need, and which, if perfected, would deprive us of that command?”

Between 1945 and 1950 the excellent minesweeping forces of World War II had literally dissolved. Ninety-nine per cent of the mine personnel during the war were Reserves and this reservoir of trained officers and men had dwindled to the vanishing point due to budgetary cuts and lack of interest in, and emphasis on, mine warfare. In 1947 the headquarters of Mine Force, Pacific Fleet were abolished. Severe reductions in minesweeper strength took place and were accompanied by a de-emphasis of training and diminishment of the importance given to mine warfare. There was little effort to improve minesweeping equipment or to develop new operational techniques. Paravanes were no longer installed on naval vessels as protection against the moored contact-type mines. Although the discovery had been made near the end of World War II that a destroyer’s sonar could be modified to pick up moored mines, the possibility had not been implemented. As far as the general service attitude in the Navy toward mine warfare was concerned, it was regarded as a task which virtually any line officer could perform when the time came. That effective mine warfare requires training, experience, and research was not generally appreciated.

As a result of these various factors, the great Pacific minesweeping fleet of World War II, which had varied between 525 and 550 ships, was no more. Instead, when the Korean War began, Commander Naval Forces Far East had six AMS’s and one AM in active commission, three AM’s in a caretaker status, and twelve Japanese minesweepers under contract. This made a total of 22 ships available in Far Eastern waters, ships which for five years had been employed generally in check-sweeping Japanese harbors and channels.

Located in West Coast yards, at Pearl Harbor, and at Guam were twelve more minesweeper type ships under command of Commander in Chief, U. S. Pacific Fleet. As there was no mine-type commander in the Pacific, these twelve vessels were split with the AM’s and AMS’s under Commander Service Force, Pacific, while Commander Cruiser-Destroyer Force, Pacific controlled the DMS’s.

The Wonsan operation was destined to focus considerable attention on the status of these forces and upon the U. S. Navy’s readiness to wage mine warfare.²

Preparations in the Far East

Directing Far Eastern minesweeper operations at the outbreak of hostilities was Commander Mine Squadron Three, Lieutenant Commander D’Arcy V. Shouldice, whose flagship, the Pledge (AM-277), commanded by Lieutenant Richard O. Young, served also as tender and logistics supply ship. In addition to his flagship, Shouldice’s force included the following ships:

Partridge (AMS-31)	Lieutenant (jg) R. C. Fuller (CoMinDiv-31)
Kite (AMS-22)	Lieutenant (jg) Nick Grkovic
Osprey (AMS-28)	Lieutenant (jg) Philip Levin
Redhead (AMS-34)	Lieutenant (jg) T.R. Howard
Chatterer (AMS-40)	Lieutenant James Patrick McMahon
Mocking Bird (AMS-27)	Lieutenant (jg) Stanley P. Gary

 

On August 3, Captain Richard T. Spofford who had much experience in the mineplanting side of mine warfare, was ordered to duty as Commander, Mine Squadron Three. Lieutenant Commander Shouldice became Commander, Mine Division 31, and immediately took the sweepers to Pusan.

Since the mine warfare problem was not foreseen in July and August of 1950, first priority for the reactivation of ships was given to amphibious types, carriers, and escort ships. In spite of this, some limited progress was made toward strengthening the force. Rear Admiral F. C. Denebrink, Commander, Service Force, Pacific, ordered the three AM’s in caretaker status at Yokosuka reactivated. On August 14 Pirate (AM-275) and Incredible (AM-249) were placed on the active list in Yokosuka. The third ship, Mainstay (AM-261), remained inactive for a time because of material shortages. COMSERPAC also deployed the Merganser (AMS-26) and Magpie (AMS-25), then at Guam, and the Pelican (AMS-32), Gull (AMS-16) and Swallow (AMS-36), then at Pearl Harbor, to the Korean theater.

Other steps were taken by Captain Spofford. Shortly after he assumed command, he reported to Vice Admiral C. Turner Joy, ComNavFE, that the squadron was not adequate to conduct assault sweeping operations against a major combatant power. He emphasized the inadequate intelligence information on enemy mines and minelaying vessels as well as the fact that he had an insufficient number of ships particularly for an assault sweep of well-planned minefields of mixed types. In late August Admiral Joy relayed these comments to Admiral Forrest P. Sherman, who was in the Far East, and asked him about the possibility of increasing minesweeping types. The Chief of Naval Operations said that because of the higher priority of other type vessels, minesweepers could not be activated for the time being. His views were concurred in by Admiral Arthur W. Radford, Commander in Chief, U. S. Pacific Fleet.

Planning and Intelligence

On October 2, Vice Admiral Arthur D. Struble riding anchor at Inchon aboard his flagship Rochester, ordered Joint Task Force Seven reformed for the Wonsan amphibious assault. Simultaneously, he ordered all Seventh Fleet minesweepers underway for the Wonsan area as soon as possible. An experienced mine warfare officer,³ Vice Admiral Struble had very little to warn him of the impending enemy’s mining effort other than isolated bits of evidence which, when added to intuition, provided less than an optimistic picture. Admiral Struble viewed the possibility of mines in Wonsan as a calculated risk. He thought the sea approaches to Wonsan were mined; that the minefields might consist of moored mines of Russian type, probably of magnetic and controlled types; that acoustic and pressure mines might be found in the area and—in addition to the mines—opposition could be expected from emplaced artillery in the Wonsan approaches.

Some of the evidence used by Admiral Struble as a basis for his rather discouraging estimate deserves examination. During the period of September 4 to September 30, UN ships and aircraft sighted mines on 54 separate occasions, most of them in the shallow Yellow Sea. To make matters worse, more than 25 floater, contact-type mines had been sighted on the surface in the high seas around Korea. It was assumed that these drifter mines had become detached from their moorings and were floating on the surface. Whether the omission of self-scuttling devices on these mines was intentional for operational reasons or a product of the need for simplicity and economy was not known.⁴

Unfortunately, some of the mines were not sighted in time. On September 26 the Brush (DD-745) struck a mine off Korea’s northeast coast. Although severely damaged, the ship limped into the Sasebo drydock on the 30th. That same day the Mansfield (DD-728) was damaged extensively enough by a mine in Chosen harbor to require stateside repair. On October 1 a mine escaped the sweeps of the Magpie and struck her starboard bow. Of the 33-man crew only twelve survived, every one of them injured. Two South Korean ships also struck mines during this period—YMS-509 on September 28 and YMS-504 on October 1. Both of these vessels managed to reach port.

There were still other dangerous signs to be sifted out for consideration. One prisoner- of-war report stated that mines had been laid around the Chongjin lighthouse in North Korea. On Wolmi-do Island in Inchon harbor, ten unassembled influence mines of Soviet make were discovered in an ox-cart. On September 27, a normal contact mine was sunk a few miles directly east of Wonsan. It was reported to have been new or freshly painted.

In spite of these numerous reports, the picture was by no means clear. The available intelligence had confirmed neither the presence nor the absence of concentrated minefields in the Wonsan or Hungnam areas. As the ships of Mine Squadron Three began departing Sasebo for Wonsan on October 6, Admiral Struble’s estimate foreshadowed the troubles ahead. Mine warfare was to be the crucial problem. In the words of Commander Harry W. McElwain, Intelligence Officer for Task Force 90, “When they said ‘go’ on the Wonsan operation, mines were our biggest headache.”

In early October the North Korean defenses on the east coast collapsed and the ROK’s advance proceeded more rapidly than had been expected. This development raised questions concerning the possibility of either an overland advance to Wonsan or a landing at a point further north on the coast. Paradoxically, most Navy men favored an overland movement to Wonsan. Their preference stemmed from several reasons. First, to outload the Tenth Corps at Inchon would seriously interfere with the unloading of incoming supplies for the Eighth Army. Second, to assemble the necessary sea lift would materially reduce the naval support available for UN forces in other areas. Third, from October 10 on, reports from the minesweepers indicated that the Wonsan landing might well be delayed. Most Army men, on the other hand, favored the sea assaults and their arguments were summed up by Major General Almond: “From a tactical point of view it’s cheaper to go to Wonsan by sea. Going overland, half of our heavy equipment would have been left in the ditches by the side of the road.” The plan to move to Korea’s east coast by sea was never changed in spite of these discussions.

On October 8, however, General MacArthur confided to Admiral Joy that he was considering a plan to invade at Hungnam rather than at Wonsan. He thought the First Marine Division might assault that port while the Seventh Division landed administratively at Iwon. Admirals Joy and Struble discussed this plan. The open beaches at Iwon suggested that the problem of mines might be greatly reduced there, and Admiral Struble felt it offered a good chance for an assault landing. Landing the Marines at Hungnam, however, was a more complicated problem, and Admiral Joy pointed out to General MacArthur that because of mines early and easy entry might be impossible, that there were insufficient landing craft to simultaneously land at two places, that the timetable for the operation was already critically tight; there was no time to shift ships, re-write plans, and all the rest. But the most important deterrent, he reminded General MacArthur, was the fact that there were far too few minesweepers to clear even one area, let alone two. Admiral Struble was in full agreement with Admiral Joy that no Hungnam change should be tried. “If anything,” he told the authors, “Hungnam represented a potentially longer sweeping problem than Wonsan. Because of the very considerable lack of minesweeping forces and experienced personnel available, only one mined area could be cleared at a time.” These naval opinions prevailed, and General MacArthur decided to continue the original Wonsan plan. It is apparent that the lack of an adequate mine warfare capability had far-reaching influence as it reduced naval flexibility and modified strategic plans.

Clearing a Path through the Wonsan Minefield

When Captain Richard T. Spofford and his small flotilla arrived off Wonsan in the chilling gray-green dawn of October 10 to commence sweeping operations, he knew little about Wonsan’s harbor except its geography and bathymetry. Only three fragments of mine intelligence were available. First, the location of the normal navigation channel published by the Soviets was known; second, a report had been received from the cruiser Worcester concerning the location of an offshore minefield near Wonsan, which had been spotted by the ship’s helicopter on October 9. And third, the earlier discovery of minefields in both Inchon and Chinnampo suggested that Wonsan probably was mined. How extensive, and what type of “cabbage patch” the Communists had planted in the harber of Wonsan itself were largely matters for conjecture.

Nor did Spofford have information concerning the military status of the numerous islands in the harbor. Were they occupied by North Korean troops? Did the islands have artillery to oppose minesweeping efforts? Had the city yet been captured by friendly troops? As for the minefields themselves, Spofford lacked even fragmentary information of how many mines had been planted in the harbor, what types they were, or where they might be located.

Had someone gratuitously handed Captain Spofford the information that the Wonsan minefield covered four hundred square miles, that it numbered more than three thousand mines, that it was a “mixed bag” of magnetic as well as contact mines, his task of sweeping the expansive Wonsan minefield would still have been an exceedingly hazardous one. The biggest handicap was a shortage of minesweepers. During World War II, the amphibious assaults against Okinawa, Leyte, and Balikpapan had been preceded by more than one hundred sweepers; at the invasion of Normandy, by three hundred. At Wonsan, Spofford’s Mine Squadron Three commenced its work on October 10 with six minesweepers.

“My first inclination,” said Captain Spofford, “was to start work in the regular navigation channel which the Soviet naval forces had been using, on the assumption that it would have been subjected to a faster and more careless mining effort because of the hasty retreat of the Soviet satellite forces.”

After careful consideration, however, with the October 15 landing date in mind, Spofford decided to risk a direct-approach sweep, sending his ships, led by the two “big steel jobs,”⁵Pledge and Incredible, on an exploratory run straight from the 100-fathom curve to the landing beaches by the shortest and most direct route. “If it worked,” said Spofford, “there was a chance we could meet the D-Day deadline.”

Shortly after sunrise on the morning of October 10, the minesweeping task got underway. The officer in tactical command, Lieutenant Commander Bruce Hyatt, was riding the Pledge, since his flagship Pirate had not yet rejoined from conducting exploratory minesweeping chores in behalf of the gunfire support ships south of Wonsan.

The Pledge began the sweep directly from the westward tongue of the 100-fathom curve in a direct line for the landing beaches where the troops were scheduled to go ashore in only five days. Astern of Pledge steamed the Incredible, Osprey, and Mocking Bird, each ship streaming its sweep gear. Two additional minesweepers followed the formation; the Chatterer dropping orange-colored conical “Dan buoys” to mark the edge of the swept channel and Partridge “riding shotgun,” to destroy by gunfire any mines brought to the surface by the other minesweepers.

To assist and expedite the sweeping, a helicopter from the USS Worcester hovered to shoreward of the minesweepers attempting to spot mines beneath the surface of the water. This would be the first instance in naval warfare of an organized and combined effort between surface ships and a helicopter to locate a minefield, although patrol aircraft and lighter-than-air ships were used in some instances and with varying degrees of success in World War II.

By late afternoon, a three-thousand-yard wide channel had been swept from the 100- fathom curve to the 30-fathom curve, a distance of about twelve miles. Twenty-one contact mines had been cut and destroyed without casualty.

“We were pleased and optimistic as the first day’s effort was about to end,” said Captain Spofford. “If the combination of Mine Squadron Three’s skillful seamanship and good luck held, I felt that we might not even need the entire time that had been allotted (by General MacArthur) to clear the channel.”

But good luck did not hold. In the late afternoon of the 10th, the Worcester helicopter suddenly dipped, lifted slightly, dipped again and again. The voice of Chief Aviation Pilot B. D. Pennington rang out the bad news: “One mine line directly ahead of Pledge.... Another line just beyond that. . . . Another . . . .” Altogether, Pennington could see five distinct lines of mines inside the 30- fathom curve, directly in the assault path to the beach. Within a few moments, all the minesweeps had verified the presence of dozens of mines from sonar echoes. As dusk fell, the sweepers filed out of the channel and anchored in swept water near the 30-fathom curve. Every officer and man was weary and somewhat taken aback by the discovery.

Efforts to Clear a Channel

After receiving the information about the extensive minefield, Captain Spofford decided to shift his sweeping effort to the Russian navigation channel. By this time his force had been augmented by the arrival of the Pirate, Redhead, and Kite. Also available was the advice of three mine experts hastily flown to the Korean theater from the east coast of the United States. These were Commander S. M. Archer and Lieutenant Commander Don C. Deforest from Mine Forces, Atlantic and Mr. Howard Naeseth from the Mine Countermeasures Station in Panama City, Florida.⁶

On the 11th the sweeping operations in the Russian channel went smoothly. As they progressed other forces were used to search for mines. From the destroyer transport Diachenko (APD-123) came frogmen who were ordered to search the surface of the harbor in their shallow draft LCPR’s. A PBM was obtained from Patrol Squadron 47 of Fleet Air Wing One. Since the 1st ROK Corps seized Wonsan during the day, steps were also taken to locate possible intelligence information ashore. After such a favorable beginning, Captain Spofford decided at a midnight conference to make an all-out effort in the Soviet channel on the following day.

All available forces were to be employed on October 12. The frogmen under the command of Lieutenant Commander William R. McKinney were ordered to reconnoiter the two outlying islands of Ung-do and Yo-do in search of mine cables which would indicate the presence of electrically-controlled mines. Helicopters and PBM’s were to continue their search missions. Spofford also tried a rarely used technique to clear the minefield: a countermining aerial strike by Task Force 77.

The Sinking of Pirate and Pledge

In the afternoon, following the air countermining attack, the minesweepers proceeded on a westerly course toward the harbor at a speed of six knots. Ahead of them were three islands: Yo-do on the left; Ung-do on the right; and Sin-do almost dead ahead. As on previous occasions, the “big steel jobs” were in the van. Lieutenant Commander Bruce Hyatt led the formation in his flagship Pirate, with Pledge and Incredible following astern. The Redhead was laying Dan buoys astern of the Pirate, while Kile was on shotgun duty astern of Incredible. Protecting the sweepers and ready to give them gunfire support were the Diachenko, Doyle (DMS-34), and Endicott (DMS-35).

At 1112 the minesweeping fleet entered unswept waters. The Pirate's ready boxes were undogged and her 3-inch gun manned as a precaution against possible enemy shore fire. Then, as quickly as it is written here, things began to happen. Two mines—their cables severed by Pirate's sweeping gear- popped to the surface. Four more followed. The mines were fifty yards apart and lay on a north-south line between Yo-do and Ung-do islands. Three minutes later, Pledge, maneuvering astern through the mines already cut by Pirate, swept three more with her port gear. Incredible, still in formation, got herself into the thick of things by cutting still another four.

At this same moment Lieutenant Commander Hyatt received information from the helicopter pilot that a large field lay dead ahead and at least three more lines of mines were in the vicinity of the sweepers. The lines were apparently bounded by the islands of Ung-do, Yo-do, Mo-do, and Sin-do, but their exact position and angle were not indicated.

Hyatt made a quick decision to abandon the original plan to turn south and to continue in the reported Russian-swept channel instead. Hyatt and McMullen considered a turn at this critical point more dangerous and continued on course. Any turn would in all likelihood expose Pirate to a mine while in the turn.⁷

The Pirate's first definite sonar report came a moment later—when the range was only one-hundred yards. Within seconds the Pirate's starboard bow lookout reported a shallow mine close aboard the starboard bow. McMullen threaded his way gingerly through the treacherous field.

There was a shattering explosion as the enemy mine exploded beneath the Pirate. A few seconds later, her stern arose from the water, exposing her propellers, then the ship fell into a boiling sea of muddy spray. The mine explosion had broken Pirate's main deck into two parts. The ship lurched to starboard, then back to port, quickly taking a list. Within four minutes she had capsized.

Pledge, commanded by Lieutenant Richard 0. Young, immediately hove to and put her motor whaleboat in the water. To add to the confusion, as Pledge’s whaleboat was being launched, previously undetected shore batteries on the island of Sin-do opened fire on the sinking Pirate and those of her crew already in the water. Pledge responded with her single 3-inch gun, whereupon the enemy fire shifted to Pledge. While this was happening, thirteen loose mines lay floating on the surface, and nearby, countless others lay undetected beneath the surface. Young’s first thought was to rescue Pirate’s survivors and continue the sweep. He was soon to decide otherwise, however, in view of the concentration of shore battery fire, plus the fact that he could not pass through Pirate’s minesweeping gear without enmeshing his own vessel. Young ordered all battle stations manned as quickly as possible to counter the concentration of fire that was coming not only from Sin-do but also in the form of small caliber fire from Yo-do island as well. Young made a quick radio call for air support and ordered his minesweeping gear cut.

The Pledge lay to and continued to fire until all her ready 3-inch ammunition had been expended. By then the shore battery on Sin-do had bracketed Pledge, and Young knew his position was fast becoming untenable. With the hope he might make a turn back into waters that had already been swept, Young ordered, “left-full rudder; starboard engine ahead two-thirds.” The ship had turned approximately thirty degrees when she struck a mine. The time was 1220. The explosion had occurred amidships on the starboard side near the forward engine room. Damage throughout the ship was extensive. Decks and bulkheads were ruptured from the keel to the open bridge. Water rushed into the hole on the starboard side. When Young, who had been temporarily knocked out by the blast, regained his senses and saw the status of both his ship and crew, he gave the order to abandon ship.

The mine-hunting patrol plane overhead, a PBM Mariner flown by Lieutenant Commander Randall Boyd, executive officer of VP-47, had discontinued its search the moment the Pirate commenced to receive surface fire. Boyd noticed gun flashes on the beach and radioed the Endicolt offering his services as aerial observer. During the next few minutes he managed to keep fully occupied by spotting the Endicolt's fire, reporting the location of survivors, making strafing runs on the enemy emplacements, and requesting an aircraft strike from the carriers.

With the Pirate down, and the Pledge sinking, the Incredible’s radio suddenly blared forth: “Dusty, Dusty, my engines are dead.” At the worst possible moment, the third and last of the “big steel jobs” had experienced complete engine failure. This meant that only Lieutenant Commander D’Arcy Shouldice’s “splinter fleet” was left to do the sweeping. Immediately these ships moved into the rescue and joined the Endicott’s gunners in taking the enemy batteries under fire with their single 40-mm and their two 20-mm guns. Under cover of this fire the Endicott’s boats pulled in the survivors. Altogether, there were ninety-two casualties from the sunken vessels—twelve missing in action and one dead from wounds after his rescue.

Thus far two attempts to open a path through the minefield had ended in failure. Both the plan to cut a direct path to the beaches and the attempt to sweep the Soviet navigation channel had been thwarted. Now the deadline for landing the Marines was only seven days away. Admiral Struble was aboard the Missouri when news came about the sinking of the Pirate and the Pledge. So serious were these developments that he transferred to a destroyer and headed for Wonsan at best possible speed to take direct charge.

As bad as this situation was, an even worse one would soon be discovered: the presence of magnetic mines.

The Discovery of Magnetic Mines in Wonsan

With the three AM’s out, two permanently and one temporarily for engine repairs, safe sweeping practices assumed paramount importance. After reviewing his predicament, Captain Spofford made the decision to marshall as many small boats and frogmen as he could, and they, in conjunction with helicopters and PBM’s spotting from above, would undertake the tedious search for mines. Under the personal supervision of Lieutenant Commander DeForest, the small boat crews took to the mine hunt like children at an Easter egg-hunt. Aided by a few sympathetic North Korean fishermen, work progressed satisfactorily, and within two days the channel had been sufficiently explored and marked for sweepers to enter with relative safety. As an additional check, Captain Spofford ordered the destroyer transport Diachenko to probe her way cautiously down the channel using the long fingers of her antisubmarine sonar in a final search for additional underwater charges.

It appeared as if the Wonsan channel was at last open. The Mocking Bird, Chatterer, Redhead, and Kite were making their last few penmanship ovals near the beaches, when, as Lieutenant (jg) T. R. Howard expressed it, “the whole ocean started to erupt amidst the sweepers.” The first 250-foot geyser about four hundred yards astern of the Redhead had not subsided when a second blast occurred six seconds later very similar to the first and not more than one hundred yards away from the first. So far, no damage had been done, except to the jangled and exhausted nerves of the sweep force themselves. Then a third explosion under the keel of ROK YMS-516 blasted that small ship into bits and pieces. In all probability, these newly found mines were the same influence type that had been discovered in the oxcarts on Wolmi-do a month earlier. If this were true, it meant that the AMS’s must now form a line parallel to the beaches about three miles out and methodically edge toward land by making pass after pass over virtually the same track.

It was not until the following morning, October 19, that the mystery concerning the type of mines disappeared. Then during a rather dramatic conference, Captain Spofford was able to announce an important discovery. “We know that there are magnetic mines; we know at least one magnetic line has been planted and we know its position quite well, thanks to the work of DeForest.”

After completing his supervisory task of buoying those contact mines that could be seen from the surface, DeForest had set out to the beach in search for some mine intelligence that was so sorely needed. In spite of sniper fire and a few hairbreadth escapes, he stuck to the task and was eventually led to an old strawstack under which he found a new Soviet-built search coil—the “eyes and ears” of a magnetic mine. In addition to this he located North Korean personnel who had helped to assemble and lay the mines, so that when he returned to Captain Spofford, he had the vital information needed to finish the job.

Although Captain Spofford now knew the combination to the Wonsan minefield, it would still require seven more days of arduous sweeping before he would have it open. Finally, on the evening of October 25, Shouldice reported to Captain Spofford that Wonsan had a swept channel “clear of mines.” A total of fifteen days had been required to complete what was supposed to have been a five-day sweep. Of the approximately 3,000 mines which had originally been planted in Wonsan, only 225 had been swept and destroyed. Probably that many or more had broken their moorings and had become floaters. But the majority of the mines, probably 2,000 or more, were still anchored in place in the minefields. “These two thousand were no longer dangerous to our operations,” said Struble, “as we knew where they were, and cleared channels to the Wonsan beach had been swept.”

How the North Korean Minefields were Laid

From an examination of the available records, it is concluded that the Communist mining campaign in Korea commenced no earlier than July 10. There is no evidence of any mine shipments or minelaying prior to that date. It is Admiral Struble’s view that the decision to commence mining was not made prior to North Korea’s initiating the war. His belief is further supported by the fact that North Korean forces were initially supplied with other types of weapons and war materials rather than mines. Moreover, it is concluded that had the Communists anticipated U. S. naval opposition, undoubtedly the mining campaign would have commenced immediately on outbreak of war in order to deny as much water as possible to our naval forces. Post-Wonsan assault intelligence reports indicated that the mining of Wonsan and Chinnampo began around August 1. This program was intensified after the fall of Inchon.

It is further concluded, based on an examination of recovered shipping labels and an examination of captured mines, that all the mines used in the Korean campaign originated from Soviet stockpiles. Most of them arrived in Korea during the period July 10-20, 1950, by rail, although there is evidence to indicate that a few were shipped by sea. Interrogation of railroad personnel at Wonsan after its capture verified the fact that about 4,000 mines passed through their hands, mainly for use in Wonsan itself but also for use at points further south. At Chinnampo, it was learned from the interrogation of prisoners that mines were shipped to Haeju by truck, that other mines were shipped to Inchon and Kunsan by rail.

It was to be later discovered that the Soviet Union had not only provided the North Koreans with mines, but with torpedoes and depth charges as well. On October 16, fourteen Soviet-built, 21-inch torpedoes were found in a tunnel near the Wonsan airstrip. With warheads attached, the torpedoes were about twenty-four feet long, and similar to the type used by the Germans in World War II. Twenty-nine depth charges weighing 300 pounds, and forty depth charges weighing fifty pounds each were found. In addition, 167 contact-type mines were found.⁸ In all, more than 600 sea mines were later discovered ashore in the Wonsan area.⁹

North Korean prisoners stated that in some instances Russian naval officers operated as far south as Inchon; that Soviet naval instructors gave mine technical training and supervised assembly of the mines in both Wonsan and Chinnampo between July 16 and August 17; that they made the adjustments of the magnetic mines that were laid in the Wonsan minefield; and that Soviet military personnel actually participated in the laying of magnetic mines. Later, at Pyongyang, one officer and three men—all North Koreans—were given training in magnetic mines. Because of the excellent mine patterns laid and their close integration with the North Korean coastal defenses, it is also concluded that Soviet personnel supervised the preparation of the Wonsan minefield.

As far as the contact mines were concerned, the evidence indicates that North Koreans did most of this work. The minelaying procedure and equipment was very simple, even primitive, in sharp contrast to U. S. Navy equipment and doctrine. Wooden barges, of a type normally used in river and coastal traffic, were equipped with iron or wooden tracks and fitted to carry ten to fifteen mines. The mines were man-loaded on the barges and towed by tug-boats into pre-determined areas where, on signal, the mines were rolled off the stern of the barges at intervals of one to one-and-one-half minutes. In this manner, about 3,000 mines were laid off the city of Wonsan in a period of three weeks.

Conclusion

The jam-packed amphibious shipping carrying the First Marine Division had filed out of Inchon between October 15 and 17. Two days later they had arrived at Wonsan only to begin what they called “Operation Yo-Yo” —steaming southward for twelve hours then northward for twelve more. This process of march and countermarch lasted until the 25th when they were finally ordered to enter the swept channel of Wonsan for an administrative landing on the following day. On October 29 the Seventh Division landed at Iwon in the same manner after the fast minesweepers, Doyle and Endicoll, reported no trace of mines in that area.

The delayed landing seemed to bring endless delight to those already ashore. Jeering placards of welcome greeted the Marines as they stepped ashore at Wonsan—one from the First Marine Air Wing, another from the enthusiastic ROKs. All such greetings struck the Marines as being somewhat excessive. But Major General Oliver P. Smith summed up the Wonsan landing very philosophically: “History just got ahead of us for once.” Even though the landing seemed to end on a light note, there were some serious and significant lessons that merited consideration.

For Captain Spofford, the minesweeping experience at Wonsan emphasized the need for including small boat sweepers in any assault sweeping operation. Had they been available there, the clearance problem might have been materially reduced. He considered it equally essential that at least one and preferably two ships with locator equipment be made available. Nor did Spofford desire to write off entirely the possibility of future counter-mine bombing. As long as there was some evidence to indicate a gap had been bombed in even one mine line, he recommended that it was a tactic deserving further experimentation.

Admiral Struble also saw several lessons in the Wonsan operation. It demonstrated that suitably-equipped helicopters can be of great value. It pointed out the need for better communications, adequate intelligence teams operated on theater level, and adequate mine counter-measure forces ready for service in each fleet.

The most serious fact of all was that the strongest navy in the world—a navy which was prepared to defeat a Communist air or submarine attack, to sink an enemy’s fleet, to do precision bombing, rocketing, and gunnery, to support troops ashore, and to enforce a blockade—had encountered a mine field off Wonsan and been compelled to steam in the Sea of Japan for over a week while a few minesweepers struggled to clear it. To many this fact meant simply that the Navy couldn’t go where it wanted to, when it wanted to. In short, the Navy did not command the sea.

Admiral Struble felt this view was exaggerated, for had the need existed to assault Wonsan it could have been done despite the mines. In view of the rapid ROK advance up the coast he decided that, “the acceptance of a very large mining risk against our heavily loaded transports would have been ‘bad judgment’ without military necessity.” Both Admiral Joy and General MacArthur had promptly approved this decision. In pointing this out, however, Admiral Struble in no way was minimizing the problem that had confronted and delayed our forces.

Admiral Joy summed it up in a manner almost everyone would agree with: “The main lesson of the Wonsan operation is that no so-called subsidiary branch of the naval service, such as mine warfare, should ever be neglected or relegated to a minor role in the future. Wonsan also taught us that we can be denied freedom of movement to an enemy objective through the intelligent use of mines by an alert foe.”