Operation Roundup ( 1951 ) Operation Roundup was an attack launched on 5 February 1951 , during the Korean War . The attack was launched by the United States X Corps toward Hongch ' on and P ' yonch ' ang . History . As an operation similar to " Operation Thunderbolt " , General Matthew Ridgway had sent orders to General Edward Almond of making contact with the enemy , determining their disposition , and if possible to discover their intentions . The X Corps plan was issued on the 1st of February for units to move out four days later , the 5th of February in 1951 . General Ridgway ' s overall intentions was to bring the Eighth Army forward to the Han River and establish a line running east along the river to Yangpyong . Having moved up to the line of Yoju - Wonju - Yongwol against little struggle , Almond was planning a strong combat reconnaissance fifteen miles above this line . Searching that deep at the corps center and do so strategically could apply pressure on the North Korean V and II Corps concentrated above Hoengsong and P ' yongch ' ang . While at the same time , the 2nd Division , due to move north along the corps left boundary , up to as far as Chip ' yong - ni , which is eight miles east of Yangp ' yong , could protect the right flank of the IX Corps as " Operation Thunderbolt " continued . At the discovery of the Chinese at the twin tunnels , General Almond ordered the 2nd Division to identify and destroy all enemy units in that area ; the 23rd Infantry received the assignment . On the 31st of January , Colonel Freeman sent his 3rd Battalion and the attached a French battalion to the tunnels , after placing the 37th Field Artillery Battalion within a thousand yards of the tunnel area for direct support . The infantry battalions reached and established a perimeter around the tunnel - bridge complex without sighting enemy forces . But from farther north , Colonel Freeman ' s forces were observed by the 125th Division , 42nd Battalion , Army . Around dawn of the 1st of February , the 375th and 374th Regiments attacked from the north and northeast , respectively ; and after daylight , the 373rd Regiment assaulted the perimeter from the northwest and southwest . In a tough , close - in fighting lasting all day , the defending battalions , relying heavily on artillery fire and on more than eighty air strikes , drew far more blood and finally forced the Chinese to withdraw . Freeman ' s forces counted 1 , 300 enemy bodies outside their perimeter and estimated total enemy casualties at 3 , 600 . Their own losses were 45 killed , 207 wounded , and 4 missing . The Attack . After three days Almond perceived that the attack on Hongch ' on was as much a battle against terrain as against enemy opposition . Resistance did stiffen after an easy opening day , but the defending forces stayed to the tops of hills and allowed the South Koreans to bring down heavy artillery concentrations and to maneuver around them . The ROK assault forces , in Almond ' s estimation , had gained confidence over the three days , substantially from the presence and support of the American artillery and tanks . As of the 8th the success of the advance thus appeared largely to depend on overcoming terrain limitations on infantry maneuver , tank movement , and artillery forward displacement .