The first, or western, phase of Operation THUNDERBOLT lasted from 25 to 31 January. The I and IX Corps moved up to twenty miles into the area south of Seoul. Only the Turkish Brigade, attached to the U.S. 25th Infantry Division, east of Osan, a major city twenty miles south of Seoul, encountered stiff resistance. Elsewhere opposition was light, and the Chinese merely conducted rearguard actions rather than hold their ground. On the twenty-sixth, Suwon, north of Osan, with its large airfield complex, was recaptured. Close air support sorties supported the advance, damaging enemy lines of communications and pounding points of resistance. As January neared its end, Chinese resistance began gradually to increase, indicating that the main enemy line had almost been reached. On 27 January the U.S. 3d Infantry Division joined the attack in the I Corps sector, and on the twenty-ninth Ridgway converted THUNDERBOLT into a full-scale offensive with X Corps joining the offensive on its eastern flank. The I and IX Corps continued a steady, if slow, advance to the Han River against increasingly more vigorous enemy defenses. On 2 February armored elements of the X Corps reached Wonju, located in the central section fifty miles southeast of Seoul. Other elements of the X Corps recaptured Hoengsong, ten miles north of Wonju, the same day.
The 96th Field Artillery Battalion winds its way through the mountains to the 1st Cavalry Division Area, 26 January 1951. (National Archives)
As part of the I Corps attack, the U.S. 25th Infantry Division advanced against stiff enemy resistance in high ground south of Seoul. One obstacle, Hill 180, an enemy strongpoint located near Soam-ni, proved particularly difficult. Capt. Lewis L. Millett of Company E, 27th Infantry, 25th Division, led his company against that hill in a dramatic bayonet and grenade assault. The tank-infantry task force to which Millett's company belonged had been held up for several days by a determined, mixed force of Chinese and North Koreans. In the resulting hand-to-hand combat, the American shock action carried the day, routing the enemy from his well-entrenched positions atop the hill. The surviving defenders fled the battlefield, leaving their equipment and weapons behind, while Millett, in the thick of the fighting, was subsequently awarded the Medal of Honor. Actions such as Millett's sustained the UN offensive despite fierce Communist resistance. On 9 February the enemy defense opposite I and IX Corps gave way. Soon UN units in the west were racing northward. The U.S. 25th Infantry Division retook Inch'on and Kimpo Airfield as elements of I Corps closed on the south bank of the Han opposite Seoul. While the three U.S. corps advanced west and into the center, General Ridgway decided to expand the offensive to the east by committing additional elements of the X Corps and the ROK III Corps (under X Corps control) in an operation code-named ROUNDUP. ROUNDUP's object was the expansion of the offensive to the central sector of the front. The X Corps' ROK 5th and 8th Divisions were to retake Hongch'on, fifteen miles north of Hoengsong, and in the process destroy the North Korean forces in that vicinity. U.S. forces supporting the movement included the 2d and 7th Infantry Divisions and the 187th Airborne Regimental Combat Team (RCT). ROUNDUP would also protect the right flank of THUNDERBOLT. Farther east, the ROK III Corps, on X Corps' right flank and still under its control, would also advance north. The operation commenced on 5 February, with both the X and the ROK III Corps attacking steadily, but against increasing enemy resistance. While UN forces in Operation THUNDERBOLT advanced to an area just south of the Han against only minor resistance, Chinese and North Korean forces were massing in the central sector north of Hoengsong seeking to renew their offensive south. On the night of 11-12 February the enemy struck with five Chinese People's Liberation Army (PLA) armies and two North Korean corps, totaling approximately 135,000 soldiers. The main effort was against X Corps' ROK divisions north of Hoengsong. The Chinese attack, dramatically announced with bugle calls and drum beating, penetrated the ROK line and forced the South Koreans into a ragged withdrawal to the southeast via snow-covered passes in the rugged mountains. The ROK units, particularly the 8th Division, were badly battered in the process, creating large holes in the UN defenses. Accordingly, UN forces were soon in a general withdrawal to the south in the central section, giving up most of the terrain recently regained. Despite an attempt to form a solid defensive line, Hoengsong itself was abandoned on 13 February.
Also on the thirteenth the Chinese broadened the offensive against the X Corps with attacks against U.S. 2d Infantry Division positions near Chip'yong-ni, on the left of the corps' front. They also struck farther to thewest out of a bridgehead south of the Han near Yangp'yong against elements of the U.S. 24th Infantry Division, holding the IX Corps' right flank. The 21st Infantry of the 24th Division quickly contained the Yangp'yong attack that was aimed toward Suwon, but at Chip'yong-ni the Chinese encircled the 2d Division's 23d Infantry and its attached French Army battalion, cleverly exploiting a gap in the overextended American lines. Chip'yong-ni was a key road junction surrounded by a ring of small hills. Rather than have the 23d Infantry withdraw, General Ridgway directed that the position be held to block or delay Chinese access to the nearby Han River Valley. An enemy advance down the east bank of the Han would threaten the positions of the IX and I Corps west of the river. Accordingly, the UN forces at Chip'yong-ni dug into the surrounding hills and formed a solid perimeter while reinforcements were mustered. The role of the Air Force was essential at Chip'yong-ni with close air support forcing the attackers to conduct their assaults only after dark. And once the enemy had cut off the ground routes, all resupply was by air. As Ridgway hoped, the 5,000 defenders of Chip'yong-ni quickly became the focus of Chinese attention. Throughout the night of 13-14 February, three Chinese divisions assaulted the perimeter, supported by artillery. The attackers shifted to different sections of the two-mile American perimeter probing for weak points. The Chinese were often stopped only at the barbed wire protecting the individual American positions, with the defenders employing extensive artillery support and automatic weapons fire from an attached antiaircraft artillery battalion. Daylight brought a respite to the attacks. True to form, the Chinese renewed their assaults the night of 14-15 February. Again the fighting was intense. During the 14 February attack, Sfc. William Sitman, a machine gun section leader in Company M, 23d Infantry, was posthumously awarded the Medal of Honor for his actions in providing support to an infantry company, in the end placing his body between an enemy grenade and five fellow soldiers. While the 23d Infantry held on at Chip'yong-ni, the situation to the southeast was grave. At the time Ridgway and Maj. Gen. Edward M. Almond, the X Corps commander, were seeking to stabilize the front line between Chip'yong-ni and Wonju, where the destruction of the ROK forces around Hoengsong had created major gaps in the defensive line. For three desperate days, the front wavered as the Chinese attempted to exploit these gaps before UN reinforcements could arrive on the scene. Ridgway acted quickly to push units into the critical areas, ordering IX Corps to move the 27th British Commonwealth Brigade and the ROK 6th Division over to X Corps and into the gap south of Chip'yong-ni. The action proved timely. On the night of 13-14 February, the Chinese conducted major assaults at Chip'yong-ni, Ch'uam-ni, five miles southeast of Chip'yong-ni, and at Wonju. But supported by massed artillery and air support, the UN forces repulsed the attacks, causing heavy Chinese casualties. To provide additional support, the IX Corps, commanded by Maj. Gen. Bryant E. Moore, now began directly assisting the X Corps in restoring the front and relieving Chip'yong-ni. On 14 February the 5th Cavalry, detached from the U.S. 1st Cavalry Division, was taken out of IX Corps reserve and assigned the relief mission. For the task, the three infantry battalions of the 5th Cavalry were reinforced with two field artillery battalions, two tank companies, and a company each of combat engineers and medics. Initially the relief force advanced rapidly, making half the twelve-mile distance to Chip'yong-ni from the main U.S. defensive line on the first day. Damaged bridges and roadblocks then slowed movement. On the morning of the fifteenth, two of the infantry battalions assaulted enemy positions on the high ground north of the secondary road leading to Chip'yong-ni. When the attack stalled against firm Chinese resistance, Col. Marcel Crombez, 5th Cavalry commander, organized a force of twenty-three tanks, with infantry and engineers riding on them, to cut through the final six miles to the 23d Infantry. The tank-infantry force advanced in the late afternoon, using mobility and firepower to run a gauntlet of enemy defenses. Poor coordination between the tanks and supporting artillery made progress slow. Nevertheless, in an hour and fifteen minutes the task force reached the encircled garrison and spent the night there. At daylight the tanks returned to the main body of the relief force unopposed and came back to Chip'yong-ni spearheading a supply column. With the defenders resupplied and linked up with friendly forces, the siege could be considered over. UN casualties totaled 404, including 52 soldiers killed. Chinese losses were far greater. Captured documents later revealed that the enemy suffered at least 5,000 casualties. The defense of Chip'yong-ni was a major factor in the successful blunting of the Chinese counteroffensive in February 1951 and a major boost to UN morale. Elsewhere on 15 February, the efforts to restore the front finally bore fruit. Rather than take advantage of the weakened front to the east, the Chinese had chosen to concentrate on eliminating the U.S. forces at Chip'yong-ni first. But they had chosen poorly, and the respite allowed Moore and Almond to restore their lines. Reinforcements, particularly the U.S. 7th Infantry Division and 187th Airborne RCT, helped the South Koreans form a solid line around Wonju and near Chech'on, twenty miles to the southwest. By the eighteenth the Communist offensive was spent, and enemy forces began withdrawing to the north rather than attempting to hold what they had taken. Such tactics would become the familiar way that the Communists would indicate the end of their offensives. Heavy casualties and the need for resupply and reorganization frequently forced the Chinese to break direct contact and pull back. UN firepower was simply too strong.
With the enemy withdrawing, Ridgway immediately ordered an advance by the IX Corps, while the X Corps moved to destroy the Communist forces around Chech'on in the central sector. By the nineteenth the initiative had completely shifted back to the United Nations Command. The new offensive became formalized on 20 February as Operation KILLER. Ridgway hoped that the name would help encourage an offensive spirit in the Eighth Army. The IX, X, and ROK III Corps were directed north toward a line, named Arizona, running from Yangp'yong east to positions north of Hoengsong and along the east-west portion of the Wonju-Kangnung highway, all about twelve to fifteen miles above the current front line. The operation was designed to enhance the damage to enemy forces and in practice proved methodical, often slowed by the spring thaw and heavy rains that swelled streams and turned roads into seas of mud. By 28 February all units had reached their KILLER objectives, in the process finally eliminating all enemy forces south of the Han River. Nevertheless, many enemy units escaped by withdrawing north under cover of inclement weather.
M4 tanks of the 89th Tank Battalion, 25th Infantry Division, cross the Han River, 7 March 1951. (National Archives)
With General MacArthur's support, Ridgway planned a new operation, code-named RIPPER, to continue the advance twenty to thirty miles northward to a new line, Idaho. Line Idaho was in an arc with its apex just south of the 38th Parallel. The major objectives of RIPPER included the recapture of Seoul and of the towns of Hongch'on, fifty miles west of Seoul, and Ch'unch'on, fifteen miles farther to the north. However, the destruction of enemy forces continued to be more important than geographical objectives. Although the removal of all Communist forces from areas south of the 38th Parallel and the restoration of South Korea's prewar boundaries remained a broad strategic objective, weakening the enemy's military power was the primary operational goal.
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