Meanwhile troops of the I ROK Corps (6th ROK Division) rapidly advanced and captured the port of Wonson without a shot being fired before the Marines arrived. The landing at Wonson became delayed due to mines in the harbor. Minesweeping commenced on 8 October.

Three large fleet sweepers, Pledge, Pirate and Incredible were not well adapted to the shallow sweeping task. Seven small wooden-hulled sweepers were added to the fleet in addition to nine Japanese and three ROK sweepers.

On the 12th both the Pledge and Pirate sank, blown up by mines. On the 18th a Japanese sweeper JMS-14 hit a mine and went down and the ROK YMS 516 met the same fate on the 19th. Meanwhile, in what became know as operation Yo-Yo the Marine Division sailed north and south, back and forth, waiting.