Operation Dauntless was a military operation performed by the United Nations Command (UN) during the Korean War designed to advance the UN lines to positions north of the 38th Parallel designated the "Wyoming Line" which would threaten the Chinese and North Korean logistics hub marked out by the towns of Pyonggang, Ch'orwon and Gimhwa-eup named the Iron Triangle. The operation immediately succeeded Operation Rugged which took the UN forces to the "Kansas Line" north of the 38th Parallel. The operation was initially successful, reaching its initial objectives, but was brought to a halt by the Chinese Spring Offensive on 22 April 1951.
Background.
On 22 March, following the successful conclusion of Operation Courageous, US Eighth Army commander Lieutenant General Matthew Ridgway notified UN forces commander General Douglas MacArthur that he was developing plans for an advance that would take Eighth Army forces above the 38th Parallel to a general line following the upstream trace of the Ryesong River as far as Sibyon-ni () in the west, falling off gently southeastward to the Hwach'on Reservoir, then running east to the coast. As in past and current operations, the objective would be the destruction of enemy troops and materiel. MacArthur approved Ridgway's concept but also scheduled a visit to Korea for 24 March, when he would have an opportunity to discuss the plans in more detail.
Upon his return to Tokyo late on 24 March, following his conference with Ridgway and a visit to the front, MacArthur announced that he had directed the Eighth Army to cross the 38th Parallel "if and when its security makes it tactically advisable. More specifically MacArthur had approved Ridgway's concept of a general advance as deep as into North Korea.
On 27 March, Ridgway assembled Corps and Division commanders at his Yeoju headquarters and advised them that ceasefire negotiations and future US Government decisions might compel the Eighth Army to adopt a static defense. Because of its inherent rigidity, such a stance would require strong leadership and imaginative tactical thinking, he warned, to stand off a numerically stronger enemy that might not be similarly inhibited in the choice of tactics. The Eighth Army meanwhile would continue to move forward and in the next advance would cross the 38th Parallel. Ridgway agreed with MacArthur's earlier prediction that a stalemate ultimately would develop on the battlefront, but just how far the Eighth Army would drive into North Korea before this occurred, could not be accurately assessed at that time.
Ridgway had revised his concept for advancing above the parallel since meeting with MacArthur on March 24. He planned to point his main attack toward the centrally located road and rail complex marked out by the towns of Pyonggang in the north and Ch'orwon and Gimhwa-eup in the south. This complex, eventually named the Iron Triangle, lay above the 38th Parallel in the diagonal corridor dividing the Taebaek Mountains into northern and southern ranges and containing the major road and rail links between the port of Wonsan in the northeast and Seoul in the southwest. Other routes emanating from the triangle of towns connected with Pyongyang to the northwest and with the western and eastern halves of the present front. A unique center of communications, the complex was of obvious importance to the ability of the enemy high command to move troops and supplies within the forward areas and to coordinate operations laterally.
The first phase of this advance was to occupy ground that could serve as a base both for continuing the advance toward the complex and, in view of the enemy's evident offensive preparations, for developing a defensive position. The base selected, the "Kansas Line", followed the lower bank of the Imjin River in the west. From the Imjin eastward as far as the Hwach'on Reservoir the line lay to above the 38th Parallel across the approaches to the Iron Triangle. Following the lower shoreline of the reservoir, it then turned slightly north to a depth of above the parallel before falling off southeastward to the Yangyang area on the coast. In the advance to the "Kansas Line", designated Operation Rugged, US I and IX Corps were to seize the segment of the line between the Imjin and the western edge of the Hwach'on Reservoir. To the east, US X Corps was to occupy the portion tracing the reservoir shore and reaching Route 24 in the Soyang River valley, and the Republic of Korea Army (ROK) III and I Corps were to take the section between Route 24 and Yangyang.
In anticipation of enemy offensive operations, Ridgway planned to pull substantial forces off the line immediately after reaching the "Kansas Line" and prepare them for counter-attacks. IX Corps was to release the US 1st Cavalry Division. The division was to assemble at Kyongan-ni, below the Han River south-east of Seoul, and prepare to meet enemy attacks aimed at the capital via Route 1 from the north-west, over Routes 33 and 3 from the north, or through the Bukhan River valley from the north-east. In the X Corps' zone, the bulk of the US 2nd Infantry Division was to assemble at Hongch'on ready to counter an attack following the Route 29 axis, and a division yet to be selected from one of the two ROK Corps in the east was to assemble at Yuch'on-ni on Route 20 and prepare to operate against enemy attacks in either Corps sector. The 187th Airborne Regimental Combat Team (187th RCT), which had left the I Corps' zone for Taegu on 29 March, meanwhile was to be ready to return north to reinforce operations wherever needed.
While these forces established themselves in reserve, Ridgway planned to launch Operation Dauntless, a limited advance toward the Iron Triangle by I and IX Corps. With the objective only of menacing the triangle, not of investing it, the two corps were to attack in succession to Lines "Utah" and "Wyoming". They would create, in effect, a broad salient bulging above the "Kansas Line" between the Imjin River and Hwach'on Reservoir and reaching prominent heights commanding the Ch'orwon-Kumhwa base of the communications complex. If struck by strong enemy attacks during or after the advance, the two corps were to return to the "Kansas Line".
On 3 April, Ridgway updated MacArthur on the operational plans. MacArthur agreed with the Operation Rugged and Operation Dauntless concept, urging in particular that Ridgway make a strong effort to hold the "Kansas Line". At the same time, MacArthur believed that the two operations would move the battlefront to that "point of theoretical stalemate" he had predicted in early March. Once Ridgway's forces reached their "Kansas-Wyoming" objectives MacArthur intended to limit UN operations to reconnaissance and combat patrols, none larger than a battalion.
Ridgway set an opening date for Operation Dauntless late on 9 April, after all but X and ROK III Corps had reached the "Kansas Line". While those two corps continued what had proved a battle more with terrain than with the Korean People's Army (KPA), I and IX Corps forces were to start toward the Iron Triangle on the 11th. "Utah", the initial objective line, arched above "Kansas" between the Imjin River and the eastern slopes of Kungmang Mountain, its trace resting on the prominent Kumhak, Kwangdok and Paegun mountain masses. The opening phase thus would be primarily an I Corps operation involving attacks by the US 3rd, 24th and 25th Divisions while requiring only a short advance by the British 27th Brigade at the left of IX Corps.
On 11 April MacArthur was removed from UN command and Ridgway was appointed in his place with General James Van Fleet assuming command of 8th Army on 14 April.
Operation.
Advance to the "Kansas" and "Utah Lines".
Since occupying positions around Yangyang above the "Kansas Line" on 10 April, the ROK I Corps had had no contact on its front, and on the 11th a company from the 29th Regiment, 9th Division, had patrolled some north of Yangyang without encountering enemy forces. The KPA 69th Brigade had been taken off the line and disbanded, and the KPA 2nd Division, now responsible for the coastal area, had yet to deploy forces in contact. The untested ROK 11th Infantry Division joined ROK I Corps. In the ROK III Corps zone high in the Taebaek Mountains, the ROK 3rd Infantry Division, despite having to be resupplied entirely by air and porters in the virtually roadless mountains, had beaten back detachments of the KPA 45th Division to reach the "Kansas Line" on 14 April, and its patrols since then had encountered few enemy forces above the line.
To the west, the three divisions of the X Corps were just beginning to consolidate positions along the "Kansas Line" on 16 April. Since the 10th, after it became obvious that KPA 1st Division forces opposite the Corps' left were withdrawing hastily eastward from the ground below the Hwach'on Reservoir, the US 23rd Infantry Regiment, 2nd Division had swung east along the lower shore in pursuit. Abandoned ammunition, food supplies, and a fully stocked aid station evidenced the enemy's haste. Ahead of the pursuing forces, the bulk of the KPA 1st Regiment (also known as the 14th Regiment) crossed the reservoir at a narrow point north-west of Yanggu, using boats and rafts that were burned after the crossing; the remainder moved to Yanggu and then north around the eastern end of the reservoir. Leading forces of the 23rd Infantry entered Yanggu and reached the "Kansas Line" on 15 April. 
The strongest KPA resistance encountered just above the Soyang River by the 7th Infantry Division at X Corps' center and the ROK 5th Division at the right had begun to dissolve on 13 April. The 5th Division cleared KPA 45th Division forces out of their defenses around Inje on the 15th, and after artillery pounded the ridges north of town during the night, dawn attacks carried the ROK to the "Kansas Line" with negligible contact. The US 17th Infantry Regiment, advancing on the 7th Division's left through decreasing opposition from KPA 15th Division forces, found Route 29 leading into Yanggu obstructed by booby-trapped fallen trees and cleverly placed wooden box mines but reached the "Kansas Line" and made contact with the 2nd Division in Yanggu on the 15th/16th. On the division's right, the US 32nd Infantry Regiment pushed through brief but sharp resistance to reach the line early on 17 April.
Beginning on the 17th, X Corps' patrols ranging above the "Kansas Line" found progressively fewer enemy forces. X Corps commander, General Edward Almond attempted to follow the KPA withdrawal by establishing forward patrol bases in all division zones, whence strong patrols were to advance farther north each day in search of KPA positions. As of 20 April the patrolling had reached a depth of about without meeting significant resistance.
On the opposite side of the Hwach'on Reservoir, IX Corps' patrols sent forward of the "Kansas Line" by the ROK 6th and 1st Marine Divisions began to bring back reports of PVA withdrawal when forces engaged in Operation Dauntless to the west drew closer to the "Utah Line". By 17 April the 1st Korean Marine Corps Regiment, which had replaced the 7th Cavalry Regiment after the latter's unsuccessful effort to capture the Hwacheon Dam, established outposts near the dam on the ridge inside the Pukhan loop and on heights above the Pukhan to the west. On the 18th a Marine patrol crossing the Pukhan west of the dam found Hwacheon town on Route 17 unoccupied except for 11 Chinese People's Volunteer Army (PVA) soldiers, whom the patrol took captive. Intelligence officers appraised the voluntary withdrawal ahead of the two IX Corps' divisions as a realignment of forces with those dropping back in the Dauntless sector, but did not overlook the possibility that the PVA were coaxing the IX Corps into a vulnerable deployment. A recently captured document, dated 17 March, extolled the virtues and explained the purpose of "roving defensive warfare," defined as defense through movement without regard for the loss or gain of ground which could "conserve our own power, deplete the enemy's strength, and secure for us more favorable conditions for future victory."
By 17 April, the first phase of Operation Dauntless had been successfully achieved. On the east flank of the advance, the 27th British Commonwealth Brigade of IX Corps had cleared minor PVA 40th Army forces from Paegun Mountain above the headwaters