While the blast of a half-ton bomb had not been powerful enough, Spofford reasoned that depth charges might start a chain reaction in which mines would detonate mines. But a precision drop by naval planes met with no success, and there was nothing left but a return to the slow, weary, and dangerous work of methodical sweeping.[76]
[76] ComNavFE OpSum 219; ComNavFE IntSum 82.
The flying boats, Mariners and Sunderlands, were called upon to assist by conducting systematic aerial searches for moored and drifting mines, which they destroyed by .50 caliber machine-gun fire. Soon an effective new technique was developed as the seaplanes carried overlays of Hydrographic Office charts to be marked with the locations of all mines sighted. These charts were dropped to the sweepers and were of considerable assistance in pinpointing literally hundreds of mines.[77]
[77] ComFltAirWing 6, “Evaluation information,” in CinCPacFlt Interim Evaluation Report No. 1, D8.
On the 18th one of the Japanese sweepers, the JMS-14, hit a mine and went down. In spite of this loss, the end seemed in sight. No attempt was being made to clear all the mines; but with a lane swept into the harbor, it remained only to check the immediate area of the landing beaches. So hopeful did the outlook appear that it was more disillusioning when the ROK YMS 516 disintegrated on 19 October after a terrific explosion in the supposedly cleared lane. Thus was TG 95.6 rudely introduced to the fact that the sweepers had to deal with magnetic mines in addition to the other types. The mechanism could be set to allow as many as 12 ships to pass over the mine before it exploded. This meant, of course, that the sweepers must make at least 13 passes over any given area before it could be considered safe.[78]
[78] Smith, Notes, 404–407; Karig, Korea, 324–326.
The Mount McKinley having arrived off Wonsan that same day, Admiral Doyle and General Almond, with six members of the X Corps staff, went by boat to the battleship Missouri for a conference with Admiral Struble. CJTF-7 asserted that he would not authorize the administrative landing until the magnetic mines were cleared from the shipping lane—a task which he estimated would take three more days. This announcement led to General Almond’s decision to fly ashore in the Missouri’s helicopter on the 20th and establish his CP in Wonsan.[79] So rapidly had the situation changed, it was hard to remember that this date had once been set as D-Day when the Marine landing force would fight for a beachhead.
[79] CG’s Diary Extracts in X Corps WD, 10–25 Oct 50; Smith, Notes, 404–405; ComPhibGruOne “Operations Report,” 11–12; LtCol H. W. Edwards, “A Naval Lesson of the Korean Conflict,” U. S. Naval Institute Proceedings, lxxx, no. 12 (Dec 54), 1337–1340; Karig, Korea, 324–326; 1stMarDiv G-1 Journal 20 Oct 50.
Operation Yo-Yo
Shortly after 1700 on the afternoon of 19 October, a rumor swept through the 250 ships of the Tractor and Transport Groups. “War’s over!” shouted the excited Marines. “They’re taking us back to Pusan for embarkation to the States.”