The Battle of the Soyang River, also referred to as the "May Massacre", or Battle of Hyeon-ri (, ) in Korean and Chinese was fought during the Korean War between United Nations Command (UN) and the Chinese People's Volunteer Army (PVA) and Korean People's Army (KPA) during the Spring Offensive of April–May 1951. The attack took place across the entire front but with the main thrust below the Soyang River in the Taebaek Mountains. The objective of the main effort was to sever the six Republic of Korea Army (ROK) divisions on the eastern front from the remainder of the US Eighth Army and annihilate them and the US 2nd Infantry Division. Secondary attacks would be mounted by PVA and KPA forces across the entire front.
The attack was launched on 16 May 1951 and succeeded in swiftly pushing back the ROK I Corps which retreated in good order and ROK III Corps which was routed, while the US 2nd Infantry Division to their left mounted a stronger defense before gradually giving up ground. By 19 May the PVA/KPA advance 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 UN launched a counterattack on the west of the front and the PVA/KPA began to withdraw after suffering heavy losses with the offensive coming to an end on 22 May.
Background Eighth United States Army commander General James Van Fleet expected the PVA's next effort to come either in the west, as had the main force of the April attacks, or on his central front. Judging the Uijongbu-Seoul, Bukhan River, and Chuncheon-Hongch'on corridors to be the most likely axes of enemy advance, he shifted forces by 4 May to place most of his strength and all US divisions in the western and central sectors and aligned the US I, IX and X Corps so that each was responsible for one of these avenues. Deployed around Seoul, I Corps blocked the Uijongbu approach with the US 1st Cavalry and 25th Infantry Divisions and the ROK 1st Division on line, and the US 3rd Infantry Division and British 29th Brigade in reserve. IX Corps, its sector narrowed by a westward shift of its right boundary, now had the British 28th Brigade, US 24th Infantry Division, ROK 2nd Division, ROK 6th Division, and US 7th Infantry Division west to east on the No-Name Line as well as the 187th Airborne Regimental Combat Team (187th RCT) in reserve for defense against an enemy strike down or out of the Bukhan River valley. In the left portion of the X Corps sector, the US 1st Marine Division and the US 2nd Infantry Division, less the bulk of the US 23rd Infantry Regiment in Corps' reserve, covered the Chuncheon-Hongch'on axis. Though the concentration of strength in the western and central areas left the remainder of the front comparatively thin, Van Fleet believed that the six ROK divisions in the east- the 5th and 7th in the right portion of the X Corps sector, the 9th and 3rd in the ROK III Corps sector, and the Capital and 11th in the ROK I Corps sector- could hold the line since opposing KPA forces were weak and since the terrain barriers of the higher Taebaek Mountains favored defense.
On 30 April Van Fleet had ordered intensive patrolling to locate and identify PVA/KPA formations as they continued to move out of contact. Patrols searching above the front during the first two days of May, however, encountered no major enemy force except at the I Corps' left where ROKA 1st Division patrols found the KPA 8th Division deployed astride Route 1. To deepen the search in the west and central areas, Van Fleet ordered patrol bases set up out along a line reaching east as far as Route 24 in the X Corps' sector. Each division fronted by this line was to establish a regimental combat team in a base position organized for perimeter defense. Patrols operating from the bases could work farther north with full fire support, and the forward positions would deepen the defense in the sectors where Van Fleet expected to be most heavily attacked. While the fortification of the No Name Line continued, the front east of Route 24 was to be advanced to to Line Missouri, both to restore contact and to clear a stretch of Route 24 and a connecting secondary road angling east to the coast for use as a supply route by the ROK divisions defending the sector. Van Fleet also directed a foray to destroy KPA forces in I Corps' west sector after the KPA 8th Division stopped short the 12th Regiment of the ROK 1st Division's attempt to establish a patrol base up Route 1 on 4 May.
The six ROK divisions in the east opened the advance toward Line Missouri on 7 May. Along the coast, ROK I Corps forces met almost no opposition, and on 9 May the ROK 11th Division's tank destroyer battalion moved some beyond Line Missouri to occupy the town of Kansong, where Route 24 ended in a junction with the coastal highway. Forces of the ROK 5th Division on the left flank of the advance in the X Corps zone reached Line Missouri the same day. The other four divisions, though still as much as short of the line on 9 May, had made long daily gains against scattered delaying forces. In the west, the bulk of the ROK 1st Division advancing up Route 1 between 7 and 9 May levered KPA forces out of successive positions and finally forced them into a general withdrawal. Setting the 15th Regiment in a patrol base 6 miles up Route 1, General Kang Mun-bong pulled his remaining forces back into his No Name fortifications.
From other bases in the I, IX, and X Corps sectors, patrols doubled the depth of their previous reconnaissance, but had no more success in making firm contact than had patrols working from the No Name Line. Available intelligence in formation indicated that the PVA 64th, 12th, 60th, and 20th Armies were completely off the west and west central fronts for refurbishing and that each of the four armies still in those sectors - the 65th, 63rd, 15th and 27th Armies - had only one division forward as a screen while remaining divisions prepared to resume the offensive. Since there were no firm indications that the resumption was an immediate prospect, however, Van Fleet on 9 May issued plans for returning the Eighth Army to Line Kansas. In the first phase of the return I, IX, and X Corps were to attack, tentatively on 12 May, towards Line Topeka running from Munsan-ni east through Chuncheon, then northeast toward Inje. ROK III and I Corps in the east meanwhile were to continue their attack to Line Missouri, a step which would carry them above Line Kansas.
On 11 May Van Fleet decided against the Topeka advance after changes in the intelligence picture indicated that PVA/KPA forces were within a few days of reopening their offensive. Air observation of enemy troops where none previously had been seen suggested forward movements under cover of darkness, reports told of large enemy reconnaissance patrols, and both agents and prisoners alleged an early resumption of the Spring Offensive. Extensive smoke screens rose north of the 38th Parallel ahead of IX Corps and above the Hwacheon Reservoir in the X Corps sector. Drawing Van Fleet's particular notice were reports that five armies - the 60th, 15th, 12th, 27th, and 20th - were massing west of the Bukhan River for a major attack in the west central sector. In further instructions for defense, Van Fleet ordered the No Name fortifications improved and directed IX Corps commander General William M. Hoge to give special attention to the Bukhan corridor, where the heaviest enemy buildup was reported. Hoge was to place the bulk of the IX Corps artillery on that flank. "I want to stop the Chinese here and hurt him," Van Fleet told Hoge. "I welcome his attack and want to be strong enough in position and fire power to defeat him." Lavish artillery fire, in particular, was to be used. If gun positions could be kept supplied with ammunition, Van Fleet wanted five times the normal day of fire expended against enemy attacks. As calculated by his supply officer, Colonel Stebbins, the "Van Fleet day of fire" could be supported for at least seven days, although transportation could become a problem since Stebbins could not haul other supplies while handling that amount of ammunition. Rations and petroleum products already stocked in corps sectors, however, would last for more than seven days.
Immediate army reserves for the advance to Line Topeka were to have been the 3rd Division, to be withdrawn from I Corps, and the newly arrived 25th Canadian Infantry Brigade. Though the Topeka advance was off, Van Fleet ordered the 25th Canadian Infantry Brigade to move north, beginning on 15 May, to Kumnyangjang-ni, southeast of Seoul, and prepare to counter any enemy penetration in the Bukhan or Seoul-Suwon corridors. The 3rd Division was still to pass to army reserve and organize forces capable of reinforcing or counterattacking in the I, IX or X Corps sectors in at least regimental combat team strength on six hours' notice. Beginning on 11 May the 15th Regimental Combat Team assembled near Ich'on, at the intersection of Routes 13 and 20 southeast of Seoul, ready to move on call into the X Corps sector; for operations in support of the IX Corps, the 65th Regimental Combat Team assembled near Kyongan-ni, southeast of Seoul and directly below the Bukhan River corridor; and the 7th Regimental Combat Team assembled in Seoul for missions in the I Corps' sector.
The six ROK divisions on the eastern front were to stay forward of the No Name Line, but were not to make further attempts to occupy Line Missouri. In the X Corps' sector, the ROK 5th and 7th Divisions, whose forces had all but reached the Soyang River southwest of Inje, were to fortify their present positions. ROK III and I Corps were to set their four divisions in fortified defenses between the lower bank of the Soyang south of Inje and the town of Kangson-ni, north of Yangyang on the coast, after conducting spoiling attacks on 12 May in the two principal communications centers ahead of them, Inje and Yongdae-ri, the latter located on Route 24 northeast of Inje. The reconnaissance company of the ROK 9th Division already had entered Inje without a fight during the afternoon of 11 May and dispersed an enemy force about a mile beyond the town before retiring on 12 May, but other forces of the two ROK Corps were prevented by distance and moderate resistance from reaching the objectives of their attacks in the one day allotted for them.
Light contact along the remainder of the front revealed little about enemy dispositions, but the composite of reports from air observers, agents, civilians, and prisoners made clear by 13 May that major PVA forces had begun to shift eastward from the west and west central sectors. Steady rain and fog all but eliminated further air observation on 14 and 15 May; poor visibility also hampered ground patrols; and a IX Corps reconnaissance-in-force by the 187th RCT up the valley northeast of Kap'yong toward what was believed to be a large concentration of enemy forces had to be canceled shortly after it started on the 15th because of the rain and poor road conditions. As much as could be determined by 16 May was that the eastward shift probably extended to the Chuncheon area.