The UN May–June 1951 counteroffensive was a military operation performed by the United Nations Command (UN) during the Korean War launched in response to the Chinese spring offensive of April-May 1951. It was the final large-scale offensive of the war that saw significant territorial changes.
By 19 May the second phase of the spring offensive, the Battle of the Soyang River, on the eastern section of the front, was losing momentum due to reinforcement of the UN forces, supply difficulties and mounting losses from UN air and artillery strikes. On 20 May the Chinese People's Volunteer Army (PVA) and Korean People's Army (KPA) began to withdraw after suffering heavy losses, simultaneously the UN launched their counteroffensive in the west and central portions of the front. On 24 May, once the PVA/KPA advance had been halted, the UN began a counteroffensive there also. In the west UN forces were unable to maintain contact with the PVA/KPA as they withdrew faster than the UN advance. In the central area the UN forces made contact with the PVA/KPA at chokepoints north of Chuncheon inflicting heavy losses. In the east UN forces had remained in contact with the PVA/KPA and progressively pushed them back north of the Soyang River.
By mid-June UN forces had reached Line Kansas approximately north of the 38th Parallel from which they had withdrawn at the start of the spring offensive and in some areas advanced to Line Wyoming further north. With the discussions for the start of ceasefire negotiations underway, the UN advance stopped on the Kansas-Wyoming Line which was fortified as the Main line of resistance and despite some limited attacks this would essentially remain the frontline throughout the next two years of stalemate.
Background On 18 May, in response to Chinese People's Volunteer Army (PVA) and Korean People's Army (KPA) attacks on the east of the front in the Battle of the Soyang River, UN commander General Matthew Ridgway suggested to US Eighth Army commander General James Van Fleet that he should attempt to relieve the pressure on his forces in the east by attacking in the west to threaten PVA/KPA lines of communication in the Iron Triangle. Ridgway recommended a two-division attack moving on the Route 33 axis towards Ch'orwon. He thought such an attack would have a good chance of succeeding since intelligence indicated that only four PVA armies occupied the sector of the front west of Chuncheon and since PVA commander Peng Dehuai would need at least a week or ten days to shift any material part of his mass from the east to oppose the advance. Nor had PVA/KPA forces on the western front shown much aggressiveness. PVA attacks had forced back some patrol base and outpost units and had tested the main line in both the US I Corps and US IX Corps sectors, but these attacks had been isolated affairs, not coordinated actions in a concerted holding operation.
Judging PVA/KPA forces in the east-central area to be clearly overextended after he reconnoitered the front on 19 May, Ridgway enlarged his concept to take advantage of their vulnerability and ordered Van Fleet to attack across the entire front. Agreeing that the PVA/KPA forces could be trapped, Van Fleet laid out an operation that he believed could produce decisive results if the attack moved fast enough. Though stabilizing the line in the east remained a problem, he now viewed that task with no great alarm even though PVA/KPA forces were deepening and strengthening their penetration. If for no other reason, he expected their logistical difficulties in the mountains to slow if not stop their advance within a matter of days; they would have created only a "long bag" that could closed behind them by rapid drives to block their main routes of resupply and withdrawal. Van Fleet's plan called for I Corps, IX Corps and part of the US 1st Marine Division at the left of US X Corps to advance on 20 May toward the Munsan-Chuncheon segment of Line Topeka. Once the Topeka segment was occupied, strikes to start closing the bag were to be made toward the Iron Triangle, one up Route 3 to secure a road center in the Yongp'yong River valley some above Uijongbu, another up Route 17 beyond Chuncheon to seize the complex of road junctions at the west end of the Hwacheon Reservoir.
Attack
West-Central sector On 20 May, with the objective of reaching the main bodies of PVA/KPA forces, including reserves, before they could organize for defensive action, I Corps' commander Lieutenant general Frank W. Milburn set his three divisions on courses for Line Topeka some above his Seoul defenses, aiming the Republic of Korea Army (ROKA) 1st Division toward Munsan, the US 1st Cavalry Division north through Uijongbu and up Route 33, and the US 25th Infantry Division north along Route 3 toward the road hub in the Yongp'yong River valley. To the east IX Corps commander Lieutenant general William M. Hoge had established an intermediate line, Georgia, whose central trace lay just above the lateral stretch of the Bukhan River dammed on the west to form the Chongpyong Reservoir and along the upper bank of the Hongch'on River emptying into the reservoir from the east. A rapid advance to Line Georgia, Hoge had believed, would allow his four divisions (the US 24th Infantry Division and the ROKA 2nd and 6th Divisions and the US 7th Infantry Division, arrayed west to east) to reach the PVA/KPA reserves.
I Corps' forces had gained ground rapidly, especially the ROKA 1st Division, which entered Munsan-ni at midmorning on 21 May, and all three divisions were on or near Line Topeka by evening of 23 May. But the attack had amounted to a futile chase as the KPA I Corps and PVA 63rd Army retreated faster than the I Corps advanced. Tank and tank-infantry forces probing well to the front of the main body of the 25th Infantry Division consistently failed to make solid contact and raised doubt that the Yongp'yong River valley road hub more than ahead of the division could be taken in time to block PVA/KPA movement through it.
Despite light resistance, the IX Corps' attack from the outset had been more cautious than aggressive. After a short advance on 20 May, Hoge sharply reprimanded his division commanders for failing to push their attacks, but gains on 21 May were even shorter. Attempting again to accelerate the advance, Hoge directed his forces to employ pursuit tactics and move no less than on 22 May, a distance that would carry them to beyond Line Georgia, far enough, if done speedily enough, Hoge believed, to break through covering forces and make contact with the main bodies of withdrawing PVA. The attack on the 22nd, however, took his four divisions no farther than Line Georgia.
In new attack orders for 23 May, Hoge made zone adjustments, obliged to do so on his right by Van Fleet's orders moving the corps boundary east as X Corps joined the counterattack. The ROKA 7th Division, after advancing in its present zone for most of the day, was to relieve 1st Marine Division forces straddling Route 29 and prepare to attack on the Chuncheon-Hwacheon axis toward the road complex at the west end of the Hwacheon Reservoir. On his left, Hoge switched the zones of the 24th Infantry Division and ROKA 2nd Division and ordered 24th Division commander General Blackshear M. Bryan to send a task force northeast up Route 17 to seize Kap'yong while the remainder of his division followed astride the road. The ROKA 2nd Division, shifting to the Corps' left flank after Bryan's forces passed through it en route to Kap'yong, was to attack northwest along secondary Route 15 toward Taebo-ri.
Still trying to animate his forces, Hoge again directed pursuit tactics and authorized them to bypass enemy groups up to company in size. His divisions advanced easily on 23 May against an accelerating withdrawal by the PVA 63rd and 64th Armies, but few units gained more than . In the deepest move, Bryan's task force of tanks and the 1st Battalion, 21st Infantry Regiment captured Kap'yong after meeting only a smattering of opposition along Route 17. Hoge nevertheless now had two American divisions positioned for advances over roads converging near the lower edge of his road center objective, the 7th Infantry Division below Chuncheon and the 24th at Kap'yong, whence a secondary valley road left Route 17 and ran northeast to rejoin it near the village of Chiam-ni ().
Eastern sector General Edward Almond's plan for the X Corps' counterattack commencing on 23 May amounted to an enlargement of limited attacks launched the day before. In the Soksa-ri () area, the 1st Battalion, 7th Infantry Regiment, had driven cross-country against hard resistance to a position commanding the lower end of a pass on the Soksa-ri-Habaejae () road about midway between the towns. Almond ordered the 3rd Infantry Division to point its general attack at the remainder of the pass and, farther north, at a road junction some due east of Habaejae where the Soksa-ri-Habaejae road connected with another road winding northeast through the higher Taebaek Mountains to Yangyang on the coast. The seizure of these objectives, ordered before the withdrawal of PVA/KPA forces from the Soksa-ri-Hajinbu-ri area became apparent, was aimed at blocking the two best roads behind the PVA. Almond reinforced the 3rd Division by attaching the ROKA 8th Division, now fully assembled in Chech'on, and also gave the ROKA 9th Division (received as a result of ROKA III Corps' inactivation on 22 May) to General Robert H. Soule along with the responsibility for the additional ground assigned to X Corps in the Hajinbu-ri area. About to attack with the approximation of a corps, Soule planned to send his 7th and 65th Regiments toward the pass and road junction, bring the damaged ROK 9th Division back into action in the Hajinbu-ri area, and keep the untried ROKA 8th Division in reserve.
Task Force Yoke, the mix of: the 2nd Battalion, 38th Infantry Regiment; the bulk of the ROKA 3rd Regiment; all but two companies of the 72nd Tank Battalion; a platoon of the 15th Infantry Regiment's tank company; a battery of the 300th Field Artillery Battalion; and a tactical air control party organized by Almond under the deputy corps commander, Colonel Ladue, had attacked through the lines of the ROKA 7th Division in the P'ungam-ni () area to seize the Habaejae road junction. A combination of difficult terrain, heavy, if spotty, resistance, and a foot-dragging performance by the South Korean troops had stopped Ladue short of his objective. For the general attack, Almond elected to replace the Yoke forces with Task Force Able, built around the 15th Regimental Combat Team (15th RCT), which was to be detached from the 3rd Division and operate under Corps' control. Once the Able force had taken Habaejae and the 3rd Division coming up from the south had captured the road junction to the east, the task force was to be dissolved and the 15th Infantry was to join the operations of its own division.
In what amounted to the beginning of one of two major spearheads of the corps counterattack, Almond on the afternoon of 22 May had sent the 187th Airborne Regimental Combat Team (187th RCT) up Route 24 to take the high ground around Han'gye (). Passing through the 23rd Infantry, General Frank S. Bowen's forces, with a battalion of the 5th Marine Regiment and two battalions of the 9th Infantry Regiment moving forward on their flanks, had driven to their objective easily against light opposition. In the counterattack, the main effort was to be made on the Route 24 axis. The 2nd Infantry Division, with the 187th RCT attached, was to drive on Inje, the 1st Marine Division to advance on Yanggu. Almond's concept was that the two spearheads would trap the enemy forces east of Route 24 and lay them open to destruction by Corps forces advancing on the right.