The U. S. destroyers _Collett_, _Swenson_, _Maddox_, and _Thomas_ were in the Wonsan area as well as the cruiser _Rochester_. On the 9th the _Rochester’s_ helicopter sighted 61 mines in a reconnaissance, and the next day the observer found them too numerous to count. In spite of these grim indications, rapid progress the first day led to predictions of a brief operation. By late afternoon a 3000-yard channel had been cleared from the 100-fathom curve to the 30-fathom line. But hopes were dashed at this point by the discovery of five additional lines of mines.[71] [71] Minesweep Rpt #1 in X Corps _WD_ 10–25 Oct 50; ComNavFE Intelligence Summary (IntSum) 76; ComNavFE Operations Summary (OpSum) 201; D/A Daily SitRpt 105; Karig, _Korea_, 315. On 12 and 13 October the naval guns of TG 95.2 bombarded Tanchon and Songjin on the northeast coast. While the USS _Missouri_ treated the marshaling yards of Tanchon to 163 16″ rounds, the cruisers _Helena_, _Worcester_, and _Ceylon_ fired at bridges, shore batteries, and tunnels in the Chongjin area.[72] [72] ComUNBlockandCortFor, “Evaluation Information,” in CinCPacFlt, _Interim Evaluation Report No. 1_, 13–15; ComSeventhFlt, “Chronological Narrative,” in _Ibid._, 7. Spofford tried to save time on the morning of the 12th by counter-mining as 39 planes from the carriers _Leyte Gulf_ and _Philippine Sea_ dropped 50 tons of bombs. It was found, however, that even the explosion of a 1000-pound bomb would not set off nearby mines by concussion.[73] According to Admiral Struble, “The results of this operation simply bore out our experience in World War II, but were tried out on the long chance that they might be effective in the current situation.”[74] [73] CTG 95.6 msg to CTF95, CTF77 11 Oct 50 in G-3 Journal, X Corps _WD_ 10–25 Oct 50; ComNavFE OpSum 215; ComNavFE IntSum 82; Karig, _Korea_, 315. [74] VAdm A. D. Struble Comments, 14 Mar 56. The 12th was a black day for the sweeping squadron. For the steel sweepers _Pledge_ and _Pirate_ both were blown up by mines that afternoon and sank with a total of 13 killed and 87 wounded. Rescue of the survivors was handicapped by fire from enemy shore batteries.[75] [75] ComPatRon 47, “Special Historical Report,” in CinCPacFlt _Interim Evaluation Report No. 1_, H4; ComUNBlockandCortFor, “Evaluation Information,” 5, 15; Karig, _Korea_, 318–322. 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.