Chinese spring offensive
The Chinese spring offensive, also known as the Chinese Fifth Phase Offensive, was a military operation conducted by the Chinese People's Volunteer Army during the Korean War. Mobilizing three field armies totaling 700,000 men for the operation, the Chinese command conducted their largest offensive operation since their Second Phase Offensive in November and December 1950. The operation took place in the spring of 1951 and aimed at permanently driving the United Nations Command forces off the Korean peninsula.
The offensive's first thrust fell upon the units of US I Corps and US IX Corps on 22 April but was halted at the No-Name Line north of Seoul by 30 April. On 15 May 1951, the PVA and Korean People's Army commenced the second impulse of the spring offensive and attacked the Republic of Korea Army and US X Corps in the east. Although initially successful, they were halted by 22 May. On 20 May, perceiving that the enemy were overextended, the US Eighth Army counterattacked the exhausted PVA/KPA forces, inflicting heavy losses.
Background
Chinese intervention
North Korea invaded South Korea on 25 June 1950. But after having conquered much of southern Korea, the KPA suffered crushing defeats after losing much of their army at the Battle of the Pusan Perimeter in early September. Outflanked by the landing at Incheon on 15 September, Eighth Army broke out of the Pusan Perimeter starting on 16 September and pursued the KPA north; in October they crossed the 38th Parallel, the dividing line between North and South Korea and invaded North Korea in turn. The Chinese government warned that to safeguard their national sovereignty, they would militarily intervene in Korea if American forces crossed the parallel. However, US president Harry Truman dismissed the warning.As the UN forces raced to the Yalu River after capturing Pyongyang on 19 October, the Chinese launched their first offensive of the war on 25 October. Undeterred, UN Commander Douglas MacArthur initiated the Home-by-Christmas offensive aimed at unifying Korea. In response, the Chinese launched their Second Phase Offensive on 25 November that forced the UN forces to retreat from North Korea in December 1950, carrying the war back south of the 38th Parallel, with Seoul being abandoned to the PVA/KPA on 4 January 1951. Reeling from these defeats, the UN Command sought to commence ceasefire negotiations with the Chinese government in January 1951, but Mao Zedong and his colleagues ardently refused; as a result, the United Nations General Assembly passed Resolution 498 on 1 February, condemning China as an aggressor, and demanded that its forces withdraw from Korea.
UN counteroffensives
The UN Command, under new commander Matthew Ridgway, began counterattacks in late January 1951 that retook Seoul from the PVA/KPA on 16 March and brought the fighting to the hills situated along the 38th Parallel. PVA commanders launched a counterattack in mid-February, with their Fourth Phase Campaign, but after gaining ground, this too was halted by UN troops in the Battle of Hoengsong and the Battle of Chipyong-ni. The PVA by this time had been badly mauled, and were worn out from incessant combat and exhaustion and their supply lines had been constantly bombed, further weakening their fighting capabilities due to lack of food and supplies.In mid-April 1951 UN forces in the central front in Korea were engaged in Operation Dauntless to advance UN positions from the Kansas Line north of the 38th Parallel to positions north of the 38th Parallel designated the Wyoming Line which would threaten the PVA/KPA logistics hub marked out by the towns of Pyonggang, Ch'orwon and Kumhwa named the Iron Triangle. The advance by US I and IX Corps was to menace the Triangle, not invest it and if struck by strong enemy attacks during or after the advance, the two Corps were to return to the Kansas Line.
US Eighth Army intelligence on 18 April warned that a PVA/KPA attack was likely any time between 20 April and 1 May but on 21 April Eighth Army commander General James Van Fleet decided to continue the Dauntless advance.
I Corps' final Dauntless objectives lay in the zones of the US 25th and 24th Infantry Divisions stretching north of the Utah Line to Ch'orwon and Kumhwa at the base of the Iron Triangle. Leading the IX Corps' advance were the ROK 6th Division and the US 1st Marine Division. In their sector the Wyoming Line curved southeast from the Kumhwa area to the Hwacheon Reservoir. On 21 April the two divisions moved above the Kansas Line against almost no opposition. Immediately west, the 24th Division did not test the opposition below Kumhwa, but deliberately stood fast in the Kwangdok-san ridges to allow the neighboring ROK 6th Division to come abreast. In the Pogae-san heights, the 25th Division attacked toward Ch'orwon, but made no substantial progress after receiving increasing artillery fire during the day and becoming involved in hard fights right at the Utah Line, especially in the zone of the Turkish Brigade along Route 33. Neither Corps developed evidence of enemy offensive preparations during the day. The absence of opposition in the IX Corps' zone only confirmed the recent patrol reports of PVA/KPA withdrawal. Below the Iron Triangle, the resistance that began to stiffen on 19 April had been expected to grow progressively heavier as I Corps' forces moved above the Utah Line. On the Imjin River front, daylight patrols working above the river again found only a scattering of PVA. I Corps' commander General Frank W. Milburn concluded in an evening wrap-up report to Van Fleet that the "enemy attitude remains defensive."
On 21 April, the Eighth Army G-2 reported that his information still was not firm enough to "indicate the nearness" of the impending enemy offensive with any degree of certainty. A worrisome fact, as he earlier had pointed out to Van Fleet, was that a lack of offensive signs did not necessarily mean that the opening of the offensive was distant. In preparing past attacks, PVA forces had successfully concealed their locations until they moved into forward assembly areas immediately before they attacked. In the US X Corps' zone north and northeast of Yanggu, US 2nd and 7th Infantry Division patrols, after several days of nearly fruitless searches, located several groups of 600-1000 immediately above the Corps' front. These groups suggested, as X Corps' commander General Edward Almond reported to Van Fleet, that a relief or reinforcement of enemy units was taking place.
Aerial reconnaissance after daybreak on 22 April, reported a general forward displacement of enemy formations from rear assemblies northwest of I Corps and north of both I and IX Corps, also extensive troop movements, both north and south, on the roads above Yanggu and Inje east of the Hwacheon Reservoir. Though air strikes punished the moving troops bodies, air observers reported the southward march of enemy groups with increasing frequency during the day. On the basis of the sightings west of the Hwacheon Reservoir, it appeared that the enemy forces approaching I Corps would mass evenly across the Corps' front while those moving toward IX Corps would concentrate on the front of the ROK 6th Division.
For the scheduled advance to the Alabama Line east of the Hwacheon Reservoir, the X Corps/ROK III Corps boundary was to be shifted west at noon on 23 April, to give the ROK III Corps, which had been operating with only the ROK 3rd Division on line, a two-division front. The III Corps' reserve division, the ROK 7th Division, began occupying the added frontage on the 22nd, its 5th Regiment relieving the ROK 36th Regiment, 5th Division and the X Corps' right early in the evening. On 23 April, the incoming division's 3rd Regiment was to move into a gap directly above Inje between the 5th Regiment and the 35th Regiment, now the right flank unit of the 5th Division. The latter's 36th Regiment meanwhile assembled below its former position in preparation for moving west into the redrawn 5th Division zone the following day as the remainder of the ROK 7th Division came into its new area. A similar shifting of KPA forces above the X and ROK III Corps was indicated when the ROK 5th Division, previously in contact with the KPA 45th Division, III Corps above Inje, captured a member of the KPA 12th Division, V Corps. Farther east, the ROK 3rd Division, which had had almost no contact since reaching the Kansas Line, received hard local attacks that drove in its outposts and pressed its main line before easing in the evening of 22 April. Thus the KPA III Corps could be shifting west toward the reservoir and the KPA V Corps returning to the line from a point above Inje eastward.
On 22 April, as I and IX Corps continued their advance toward the Wyoming Line. The progress of the attack resembled that on the previous day, IX Corps' forces making easy moves of, the two I Corps divisions being limited to shorter gains by heavier resistance. On the east flank of the advance, the Hwacheon Dam, defended so stoutly by PVA 39th Army forces only a few days earlier, fell to the 1st Korean Marine Corps Regiment without a fight. But a PVA captive taken elsewhere in the 1st Marine Division zone during the afternoon told interrogators that an attack would open before the day was out. In mid-afternoon the ROK 6th Division captured several members of the PVA 60th Division and, immediately west, the US 24th Infantry Division took captives from the PVA 59th Division. These two divisions belonged to the fresh 20th Army. The full IX Army Group had reached the front. In the US 25th Infantry Division's zone on the west flank of the advance, six PVA who blundered into the hands of the Turkish Brigade along Route 33 during the afternoon were members of a survey party from the PVA 2nd Motorized Artillery Division. The division's guns, according to the officer in charge, were being positioned to support an attack scheduled to start after dark.