The Battle of Kumsong, also known as the Jincheng Campaign (), was one of the last battles of the Korean War. During the ceasefire negotiations seeking to end the Korean War, the United Nations Command (UNC) and Chinese and North Korean forces were unable to agree on the issue of prisoner repatriation. South Korean President Syngman Rhee, who refused to sign the armistice, released 27,000 North Korean prisoners who refused repatriation. This action caused an outrage among the Chinese and North Korean commands and threatened to derail the ongoing negotiations. As a result, the Chinese and KPA decided to launch an offensive aimed at the Kumsong salient. This would be the last large-scale Chinese offensive of the war, scoring a victory over the UNC forces.
Background The Chinese People's Volunteer Army (PVA) and the Korean People's Army (KPA) objective was the bulge in the U.S. Eighth Army lines that began roughly about northeast of Kumhwa, extended northeast to the hills south of Kumsong, leveled off to the east for about , then dipped to the southeast for some to the village of Mundung-ni, northwest of Heartbreak Ridge. Since the terrain was very rough, ranging from hills 400 to 600 meters high in the west to somewhat over 1,000 meters at the eastern end of the bulge, the Republic of Korea Army (ROK) troops defending the sector had great difficulty in maintaining lateral lines of communication. Five ROK divisions manned positions in the bulge, with the ROK Capital Division of the U.S. IX Corps on the left flank, the 6th, 8th and 5th Infantry Divisions of the ROK II Corps in the center, and the ROK 20th Infantry Division of the U.S. X Corps on the right. The ROK 3rd Infantry Division was II Corps reserve. Facing the ROK forces were three PVA armies. During the early days of June they had brought in the 68th Army and placed it between the 60th and 67th Armies. In addition, the Chinese had strengthened the 60th Army by attaching to it the 33rd Division. Thus, the PVA had available for the attack on the bulge four new divisions that had been training on a similar type of terrain in the rear.
Battle Initial assault (11–18 June) For the first ten days of June the PVA/KPA had been deceptively quiet on the central front. Then, on the evening of 10 June, the artillery fire became intense and the PVA followed up with coordinated attacks ranging from a battalion to a regiment in strength on the sector held by the ROK 5th Division. Using elements of both the PVA 68th and 60th Armies, the PVA began to build up the pressure. Smashing through the outposts, the PVA seized Hills 973 and 882, northwest of Heartbreak Ridge and part of the main line of resistance. ROK II Corps quickly released the 22nd Regiment of the ROK 3rd Division to the operational control of the ROK 5th Division to redress the PVA inroads on 11 June. Elements of the ROK 35th Regiment counterattacked to recapture Hill 973, but were only partially successful. PVA units swiftly moved to the offensive again and forced the ROK troops to pull back 1,000 meters south of Hill 973. Two battalions of the 22nd Regiment attempted to regain Hill 882 that same day and were able to approach the crest and dig in. Using the 22nd, 27th and 35th Regiments to launch counterattacks on 12 June, the ROK 5th Division was unable to drive the Chinese off the hills. Heavy artillery, mortar, and small arms fire, coupled with the PVA's willingness to reinforce his units and counterattack the ROK assault forces, prevented the UNC troops from recouping their terrain losses.
The Chinese broadened the pressure upon the ROK II Corps on 12 June by attacking elements of the ROK 8th Division on the left flank of the ROK 5th Division. In the Capitol Hill sector, northwest of Hill 973, which was defended by the 21st Regiment, the PVA used two companies initially, reinforced later with three more, and penetrated first the outposts and then the main line positions of the regiment. Two battalions of the ROK 10th Regiment moved up to counterattack early on the morning of 13 June, but were unable to restore the original line. Another PVA attack by an estimated two companies during the afternoon forced the abandonment of a company outpost and further withdrawal by the ROK forces. The next morning the Chinese continued the offensive, employing several companies to sustain pressure against the 21st Regiment. Although the ROK units fought off these drives, disaster struck on the evening of 14 June. First a reinforced battalion enveloped the 3rd Battalion of the 21st, causing it to break up into small groups fighting independently to regain UNC lines. Two PVA companies then hit the main line positions of the 1st Battalion and forced it to pull back. A third attack by a reinforced battalion succeeded in enveloping the 2nd Battalion. Assembling behind the lines, the remnants of the 21st managed to establish a new main line of resistance that was to prove short-lived. On the right flank of the ROK 5th Division, the ROK 20th Division of U.S. X Corps, guarding the sector known as Christmas Hill, southeast of Hill 882, had also been subjected to attack. On 10 June two companies from the PVA 33rd Division captured a company outpost on the approaches to Hill 1220, part of the Christmas Hill area. The ROK 61st Regiment counterattacked, rewon, and then relost the outpost. Further action to regain the position was suspended as the gravity of the situation on the ROK 5th Division front increased. When the PVA showed that they intended to retain possession of Hills 973 and 882, which were located on the main ridge leading to Hill 1220 from the west, the X Corps commander, Lieutenant general Isaac D. White, moved up the ROK 7th Infantry Division, the Corps' reserve, and placed it on the left flank of the ROK 20th Division. While the ROK 7th Division was advancing north, the 61st Regiment made several efforts to relieve some of the pressure on the ROK 5th Division. The Chinese reacted quickly and managed to blunt each attack.
On 14 June the PVA 33rd Division renewed the offensive against the ROK 5th and 20th Divisions and forced the former to fall back south of the Pukhan River. This withdrawal exposed the flank of the ROK 7th Division, which had just reached its defensive lines. The Chinese this time failed to reorganize their attacking force quickly enough. X Corps artillery and Fifth Air Force close air support were concentrated on the PVA units facing the ROK 5th Division, while the ROK 7th readjusted its front-line positions to tie in with the new ones established by the ROK 5th. On the other flank of the 5th, the ROK 8th Division also had to retreat over to tie in its main line of resistance with its sister division on 15 June. The two remaining regiments of the ROK 3rd Division were ordered on 15 June to assume responsibility for the sector east of the 8th Division along the south bank of the Pukhan River, where they served to strengthen the left flank of the ROK 5th Division. As the ROK 3rd Division took over its defensive positions, the ROK 22nd Regiment reverted to the control of its parent unit. At the same time the ROK 5th Division was attached to X Corps, which became responsible for the ground east of the Pukhan. X Corps immediately made efforts to speed supplies and equipment forward to the ROK 5th Division and to replace its personnel losses. Since lateral roads were scarce, twelve H-19 helicopters were allocated to help out and they lifted a quarter of a million pounds of material forward to the front. On 16 June the ROK 11th Division shifted over from the ROK I Corps area to become ROK II Corps reserve.
The action tapered off during the next few days. In the ROK 8th Division territory west of the Pukhan on 16 June the PVA overran an outpost of the ROK l0th Regiment on Finger Ridge, east of Capitol Hill, but the Chinese units broke contact and withdrew that evening. The ROK 21st Regiment repelled several company-sized attacks during the day. Later, aided by the 19th Regiment of the ROK 6th Division, the 21st Regiment mounted a counterattack and the PVA pulled back. Two PVA companies penetrated the main line positions of the ROK 16th Regiment, 8th Division, southeast of Finger Ridge, but did not attempt to follow up the breakthrough. By the evening of 16 June, PVA operations on the 8th Division front had become sporadic. During the next two days, the PVA launched several minor assaults on the ROK 20th and 8th Divisions, effecting slight penetrations. By 18 June the situation began to stabilize and the Eighth Army had an opportunity to survey the damage of the nine-day offensive.
The PVA had driven the ROK forces back an average of 3 km along a 13 km front and in the process had taken over a series of hill positions east of the Pukhan River. As a result of the Chinese drive, three ROK divisions had been redeployed in reinforcing and counterattacking roles. During the action the ROK units had taken a total of over 7,300 casualties, while PVA losses were estimated at over 6,600. In close support of the UNC defense, Air Force, Navy and Marine aircraft had flown 810 sorties in the nine-day period and the strategic air program had been delayed.
Interregnum (26 June – 12 July) The UNC had spent the quiet period reorganizing the battered ROK 5th Division and by 26 June the division was judged ready for action once again and control was returned to ROK II Corps. In the meantime the ROK 7th Division had taken over the ROK 20th Division's positions on the right flank of the ROK 5th Division. During the night of 26 June the PVA 179th Division of the 60th Army dispatched one regiment against elements of the ROK 5th Division east of the Pukhan River and a second regiment against units of the ROK 7th Division on the main ridge leading to Hill 1220. Heavy artillery and mortar fire accompanied the attacks and the PVA pressed on vigorously despite a staunch defense by both ROK divisions. As the ROK 5th stubbornly gave ground and retreated to the next terrain line, the ROK 7th also had to pull back to protect its left flank. The PVA pressed on and managed to penetrate the ROK 7th's positions on Hill 938 just northwest of Hill 1220. For several days the ROK 7th counterattacked to regain Hill 938, but the PVA refused to yield possession. The PVA held the hill with a small force and permitted the ROK troops to move in, then directed heavy artillery and mortar fire on the area and counterattacked in mass. After several experiences along this line and study of the growing list of ROK casualties, White shifted to a policy of containment on 3 July. Terrain to the rear was readied for defense and helicopters rushed up materials and ammunition to prepare the new fortifications for further attacks. The Chinese made two attempts on 4 July to move in closer to Hill 1220, but the ROK 7th Division fought off both of these assaults.