From On Desperate Ground: The Marines at The Reservoir, the Korean War’s Greatest Battle, by Hampton Sides (Doubleday, 2018), Kindle pp. 71-72:
The troopships of X Corps departed Inchon in mid-October and sailed down the coast through the Yellow Sea. The convoy of more than seventy vessels passed Kunsan and Mokpo and rounded the peninsular horn, swerving through a confusion of coastal islands and then turning into the Korea Strait. From the railings, off the port side, the men could see the liberated siege grounds of Pusan, site of so much brutal fighting only a little over a month earlier. Then the transports turned into the stormy Sea of Japan and worked their way up the east coast, past Yeongdeok and Samcheok, past Donghae and Yangyang. Finally they crossed into North Korean waters and steamed for Wonsan, a port city of 75,000 people tucked into a large bay a little more than a hundred miles north of the thirty-eighth parallel.
But as they approached Wonsan, to the men’s consternation, the ships turned around and started sailing back down the coast for Pusan. No one seemed to know why. Had their orders changed? Was the war over? Were they going home? Then the ships turned around once again, resuming their northward crawl—only to be followed by yet another turn. The Marines and soldiers of X Corps, crammed into their vessels, didn’t understand what was happening.
Eventually the word sifted through the ranks: The North Koreans, working with Russian experts, had mined the waters off Wonsan. Having anticipated that the U.N. forces might land here, they had gone out into the harbor in diverse local craft—barges, junks, tugboats, fishing sampans—and sown the waters with explosives, mostly Russian-made. The harbor was infested: Thousands of contact mines and magnetic mines bobbed just beneath the surface.
So American minesweepers, along with teams of Navy frogmen, were brought in to clear the approaches to the harbor. More than two dozen of these peculiar vessels went to work, often with helicopters buzzing overhead to serve as spotters. Minesweepers had elaborate wire structures, extending far out from the bows, that were equipped with various floats, depressors, and cutters strong enough to sever the steel cables that often moored mines to the seabed. The sweepers plied the harbor, clearing one long channel at a time, even as North Korean artillery shelled them from shore.
It was tedious but also perilous work: On October 10, two American minesweepers missed their quarry and were blown apart. Twelve men died in the explosions, and dozens more were wounded. A week later, a South Korean minesweeper was also destroyed. The men found one mine—also Russian-made—that had a particularly diabolical design. A dozen ships could pass over it without incident, but the thirteenth ship would cause it to detonate. “It took a curious sort of mind to come up with a notion like that,” wrote one Marine, wondering if the number thirteen had a “sinister connotation for Russians as it did in the States.”
Given the dangers in the harbor, the X Corps landing obviously would have to be delayed until the sweepers had completed their painstaking task. And so the troopships churned back and forth along the coast—changing direction every twelve hours. The Marines dubbed this endless backtracking the “Sail to Nowhere” and “Operation Yo-Yo.” For nearly two weeks, they remained at sea with little to do but watch the dull landforms slide by. As food supplies dwindled, the galleys served mustard sandwiches, glops of fish-head chowder, and other highly dubious fare. Joe Owen, of the Seventh Marine Regiment, called it an “ordeal of misery and sickness, malaise and dreariness. The holds stank of unwashed bodies and sweaty clothes.” As one Marine account put it, “Never did time die a harder death.”
What made their seaborne imprisonment more difficult to take was their discovery, by radio, that Wonsan had already been pacified. Republic of Korea troops, working their way overland from Seoul, had arrived in Wonsan and quelled all enemy resistance there. The First Marine Air Wing had set up shop at a nearby airfield, and planeload after planeload of men and supplies had safely landed. The zone around Wonsan was deemed so peaceful, in fact, that the entertainer Bob Hope had already dropped in to perform one of his USO comedy routines for the aviators—during the show, he boasted of how he and his dancing girls had beaten the famed leathernecks ashore.