The Battle of Triangle Hill, also known as Operation Showdown or the Shangganling Campaign (), was a protracted military engagement during the Korean War. The main combatants were two United Nations (UN) infantry divisions, with additional support from the United States Air Force, against elements of the Chinese People's Volunteer Army (PVA) 15th and 12th Corps. The battle was part of UN attempts to gain control of the "Iron Triangle" and took place from 14 October to 25 November 1952.
The immediate UN objective was Triangle Hill (), a forested ridge of high ground north of Gimhwa-eup. The hill was occupied by the veterans of the PVA's 15th Corps. Over the course of nearly a month, substantial US and Republic of Korea Army (ROK) forces made repeated attempts to capture Triangle Hill and the adjacent Sniper Ridge. Despite clear superiority in artillery and aircraft, the escalating UN casualties resulted in the attack being halted after 42 days of fighting, with PVA forces regaining their original positions.
Background
By mid-1951 the Korean War had entered a period of relative stalemate. With the resignation of Dwight D. Eisenhower as the Supreme Commander of the North Atlantic Treaty Organization (NATO) in June 1952, General Matthew Ridgway of the United Nations Command was transferred from Korea to Europe as Eisenhower's replacement. The United States Army appointed General Mark Wayne Clark, commander of the US Fifth Army during World War II, to overall command of the UN forces as a replacement for Ridgway.
General James Van Fleet commander of the Eighth US Army had hoped that the change of commanders would allow him to reengage the PVA in a major campaign, but in an effort to limit UN losses during the peace talks in Panmunjom, Clark repeatedly overruled Van Fleet's requests for an authorized offensive into North Korean territory. In September 1952, Van Fleet submitted tentative offensive plans for Operation Showdown, a small-scale offensive drafted by US IX Corps as a ridge-capturing operation. The goal of the submitted plans was to improve the defensive line of the US 7th Infantry Division north of Gimhwa near Triangle Hill, pushing the PVA defensive line back .
In September 1952, the negotiations at Panmunjom began to deteriorate, primarily due to Sino-North Korean insistence that all prisoners of war be repatriated to their respective original countries, regardless of their preferences. As a significant number of Chinese and North Korean POWs had been forced, tortured with death threats and expressed their desire to defect permanently to South Korea or Taiwan, the demand was met with strong opposition from the United States and South Korea. Feeling that the negotiations would soon fail, military commanders on both sides authorized numerous tactical plans as means of applying pressure on their opponents. In late September, the PVA High Command authorized the tactical plans which led to the Battle of White Horse Hill. On 8 October 1952, truce negotiations officially ceased. Clark gave his consent to Operation Showdown the same day.
Prelude
Locations and terrain
Sanggam-ryŏng, or Triangle Hill as it was named by the UN command, was a forested hill that appeared as a V shape when seen from the air or on a map. Hill 598 sat at the tip of the V and overlooked the Gimhwa valley less than to the south. From this apex, two ridges extended to the northeast and northwest. The ridge to the northwest is dominated by a hill nicknamed "Pike's Peak". The other connects to a pair of hills that had been dubbed "Jane Russell". A less-prominent ridge, named Sandy, sloped down to the east. Across the valley from Sandy stood Sniper Ridge, located at .
Forces and strategies
The original plan for Operation Showdown called for simultaneous attacks on both Triangle Hill and Sniper Ridge. One battalion from the US 31st Infantry Regiment, 7th Infantry Division would take Triangle Hill from Gimhwa-eup, while one battalion from the ROK 32nd Regiment, 2nd Infantry Division would attack Sniper Ridge along a parallel northbound route. UN planners expected the operation to last no more than five days with 200 casualties on the UN side, based on the assumption that maximum artillery and air support would be available. Before the plan could be carried out, however, the artillery and air assets for this operation were diverted to the Battle of White Horse Hill. Upon reviewing the situation, Colonel Lloyd R. Moses, commander of the US 31st Infantry Regiment, doubled the American strength just before the offensive.