Operation Roundup was an advance by United Nations Command (UN) forces during the Korean War that took place from 5 to 11 February 1951. While achieving initial success against limited opposition, it was brought to a halt by Chinese People's Volunteer Army (PVA) and North Korean Korean People's Army (KPA) forces at the Battle of Hoengsong.
Background When US X Corps commander General Edward Almond received a request from Eighth Army commander General Matthew Ridgway on 30 January for an X Corps - Republic of Korea Army (ROKA) III Corps operation similar to Operation Thunderbolt, he was in the process of extending X Corps' diversionary effort ordered earlier by Ridgway. Having achieved the Yoju-Wonju-Yongwol line against little opposition, Almond was planning a strong combat reconnaissance above this line. Searching that deep at Corps' center and right could apply pressure on the KPA V and II Corps concentrated above Hoengsong and Pyongchang. At the same time, the US 2nd Infantry Division, due to move north along the Corps' left boundary as far as Chip'yong-ni, east of Yangp'yong, could protect the right flank of US IX Corps as Operation Thunderbolt continued.
As shown by the Battle of the Twin Tunnels, the PVA appeared determined to retain control of Chip'yong-ni. They had good reason as the town was situated so that the force occupying it could control movements over Route 2 to the west, over Route 24 to the northeast, over Routes 24 and 24A below town, and thus through the Yangp'yong-Ch'ungju segment of the Han River valley stretching to the southeast behind it. Eighth Army possession of Chip'yong-ni, furthermore, would pose a threat of envelopment to enemy forces opposing US I and IX Corps below the Han River. For these same reasons Almond planned to seize Chip'yong-ni and incorporated this plan in his overall recommendations for an operation styled on Operation Thunderbolt. Also behind Almond's proposals were late January intelligence reports of a strong enemy force assembling around Hongcheon, at the intersection of Routes 24 and 29, northeast of Chip'yong-ni and north of Hoengsong. This force, apparently part of the KPA V Corps, could be preparing to advance southwest on Route 24 through Chip'yongni, then down the Han valley toward Yoju and Ch'ungju. Or the V Corps might again push forces south on Route 29 through Hoengsong toward Wonju. To spoil either move, Almond considered Hongcheon the proper main objective of an X Corps' attack. To disrupt both the KPA V Corps and II Corps, he outlined a coordinated X Corps-ROKA III Corps advance, Operation Roundup.
The current Corps' combat reconnaissance limit, generally the Chip'yong-ni-Hoengsong-Pyongchang line, was to be the line of departure for the operation and was to be occupied in a preliminary advance by the 2nd Infantry Division on the left, the 187th Airborne Regimental Combat Team (187th RCT) in the center, and the US 7th Infantry Division on the right. This advance would base US units far enough forward to support a thrust at Hongcheon, which Almond planned ROK forces would make. He proposed a flanking operation against Hongcheon by the ROKA 5th and 8th Infantry Divisions accompanied by artillery and armor drawn from the US units on the line of departure. From behind the 2nd Division on the left, part of the ROKA 8th Division was to advance north over Route 29 while the main body moved northwest to cut Route 24 roughly halfway between Chip'yong-ni and Hongchon, then turned northeast to hit Hongcheon itself. On the right, the ROKA 5th Division was to advance north through the mountains east of Route 29 through part of the area occupied by the KPA II Corps, then swing west against Hongch'on. The 2nd Division was to appoint one light artillery battalion, a medium battery, an automatic weapons battery and a motorized infantry battalion to move with and directly support the ROKA 8th Division. These units eventually constituted Support Force 21. The 7th Division was to furnish a similar Support Force 7 for the ROKA 5th Division. In each instance the artillery commander of the US division was to coordinate all artillery fire within his own zone and within the zone of the ROKA division he was supporting. Later, because control of the ROKA advance was centralized at Corps' headquarters and did not involve either US division headquarters per se, a question-warranted or not-would arise over who should order the displacement of these support forces. Five armored teams, each comprising a company of infantry and a platoon of tanks, also were designated, two by the 2nd Division, two by the 7th Division and one by the 187th RCT. Only three were used. Teams A and B from the 2nd Division were attached to the ROKA 8th Division at the outset of the advance; Team E from the 187th RCT later opened operations under the control of the Corps' armored officer.
By 5 February, the date set for opening the Hongchon strike, Almond expected ROKA III Corps to have come up even with X Corps’ line of departure. On the 5th ROKA III Corps should start forward through successive phase lines, coordinating each phase of movement with X Corps’ progress, to destroy KPA II Corps forces in zone and to protect X Corps' right flank. Ridgway approved Almond's plan on 1 February and made Almond responsible for coordinating the X Corps and ROKA III Corps attacks. Ridgway cautioned him, however, that for the remainder of Operation Thunderbolt his continuing mission of protecting the IX Corps' right flank would be X Corps' overriding tactical consideration. The next day Ridgway ordered ROKA I Corps to capture the east coast town of Gangneung in an advance coordinated with the progress of ROKA III Corps. X Corps’ preliminary advance to the line of departure was largely but not fully effected by the target date. At the Corps' west flank, the 23rd Infantry Regiment moved north of the Twin Tunnels and occupied Chip'yong-ni, surprisingly against no more than token opposition. At Corps' center, the 38th Infantry Regiment, now commanded by Colonel John G. Coughlin, occupied Hoengsong, and the 187th RCT the ground immediately southeast. The 7th Division at the Corps' right was not yet on the line. Its 17th and 31st Infantry Regiments were still approaching over the Chech'on-Pyongchang and Yongwol-Pyongchang roads. Behind the line traced by these clumps of Americans, the ROKA 5th and 8th Divisions were in final assemblies for the Hongcheon attack, one on either side of Route 29.
The assault divisions of ROK III Corps, the 7th and 9th, also were somewhat short of the line of departure on the 5th, yet near enough to satisfy Almond. The day before, at a Corps' commanders’ conference at Suwon, he notified Ridgway that he was ready to begin Operation Roundup. Ridgway that day ordered a westward shift of the X Corps-ROKA III Corps boundary to give the ROKA more of the territory north of Pyongchang. Hence, when Roundup opened at 08:00 on the 5th, General Yu Jae-hung's two divisions faced the bulk of the KPA II Corps while Almond's two assault units confronted the KPA V Corps in the Hoengsong-Hongch'on area.
Advance
Although the advance started in the Thunderbolt pattern, the harsh mountains ahead of X Corps and ROKA III Corps inhibited a complete ground search such as I and IX Corps were making. In X Corps' zone, the ROKA 5th and 8th Divisions advanced in multiple columns astride the best roads, tracks, or trails permitting passage through the convoluted ground. The ROKA troops climbed the higher ridges only when necessary to reduce an enemy position. The main routes for the 8th Division were Route 29 and a mountain road-actually a poor stretch of Route 2-reaching west from Route 29 at a point above Hoengsong. The 5th Division's principal paths followed the upstream traces of two small rivers east of Route 29. Physical contact between columns was rare, especially in the 8th Division zone where the columns diverged as they proceeded north and northwest. After three days Almond perceived that the attack on Hongcheon 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 ROKA to bring down heavy artillery concentrations and to maneuver around them. The ROKA assault forces, in Almond's estimation, had gained confidence over the three days, substantially from the presence and support of the US artillery and tanks. As of 8 February the success of the advance thus appeared largely to depend on overcoming terrain limitations on infantry maneuver, tank movement, and artillery forward displacement.
Against the combination of enemy hilltop defenses and difficult terrain, the two ROKA divisions by 8 February had moved northwest, north, and northeast of Hoengsong. Almond decided on the 8th that the ROKA 8th Division's main effort to envelop Hongcheon from the west could be eased by committing another division. Currently, one of the 8th Division's regiments was moving north astride Route 29 while the other two were pushing through rough ridges to the northwest to cut Route 24. If Almond set another force in the center to move up Route 29, the 8th Division could make its enveloping move in full strength. Almond mistrusted his own reserve division, the ROKA 2nd Infantry Division, still weak from losses in the PVA New Year's Offensive. He chose not to reduce the strength of the US 2nd or 7th Division defenses along the line of departure, and he could not use the 187th RCT, because on 4 February Ridgway had notified him that they were scheduled to be taken off the line and that he was not to give them an offensive role. On the 8th Almond asked Ridgway for the ROKA 3rd Infantry Division, then in ROKA III Corps' reserve. Ridgway hesitated to take Yu's only reserve. On the other hand, Yu's assault divisions were reporting good progress through light to moderate resistance. Moving astride Route 60 from Pyongchang toward Ch’angdong-ni, to the north, the ROKA 7th Division had advanced one regiment within of the latter town. On the Corps' right, the ROKA 9th had moved above Chong-son through the upper Han valley for almost . Since Yu could get help from the US 7th Division, whose 31st Regiment was now following the ROKA 7th Division above Pyongchang, Ridgway agreed to the transfer of the ROKA 3rd Division for the duration of the operation and Almond instructed the division to be in position for an advance above Hoengsong on the morning of the 11th.