Triangle Hill earned its name from the V-shape it traced on aerial photographs. Hill 598 sat at the apex, overlooking the Gimhwa valley to the south. Two ridges extended northeast and northwest -- the northwestern one dominated by a peak nicknamed Pike's Peak, the other connecting to a pair of hills soldiers had dubbed Jane Russell. Across the valley stood Sniper Ridge. Together, these positions formed part of the Iron Triangle, the strategic zone that had defined the Korean War's central front since 1951. The Chinese 15th Corps held the hills with veteran troops who had excavated 9,000 meters of tunnels, plus extensive trenches, obstacles, and minefields. A ROK staff officer had defected to the Chinese before the battle carrying a complete copy of the UN attack plan, but the Chinese command did not take the intelligence seriously.

The opening bombardment on October 14 stripped the foliage from Triangle Hill and destroyed most above-ground fortifications. But the defenders were underground. As US and ROK troops approached, they were met with grenades, Bangalore torpedoes, shaped charges, and rocks thrown from tunnel mouths. The 31st Infantry Regiment wore ballistic vests in one of the first mass deployments of modern body armor, but the fighting was at a range where such protection mattered less than the Chinese willingness to absorb punishment and counterattack after dark. Night after night, PVA assault troops charged through their own artillery screens to reach UN positions -- a tactic so desperate that American observers suspected the attackers were drugged, though no evidence supported this. The defending company on Sniper Ridge was reduced to 20 survivors before withdrawing into the tunnels.

By late October, PVA acting commander Deng Hua recognized a strategic opportunity: if China could absorb the losses, the battle would exhaust American willingness to attack. On October 25, the 15th Corps was ordered to retake the hills "regardless of the cost." Fresh reinforcements arrived -- the 12th Corps was placed under 15th Corps command, 1,200 new recruits replenished shattered companies, and 67 heavy guns were brought forward. On October 30, the 15th Corps unleashed the largest Chinese artillery barrage of the war: 133 large-caliber guns, 22 rocket launchers, and 30 heavy mortars. Ten infantry companies swarmed the ROK positions after midnight and pushed them off the summit. The seesaw fighting continued for weeks, each side retaking and losing ground in a rhythm of bombardment and assault that consumed men and ammunition at a staggering rate.

On November 5, Lieutenant General Reuben Jenkins, commanding US IX Corps, suspended attacks on Triangle Hill. The Chinese had suffered an estimated 11,500 casualties, with many units nearly destroyed, but their ability to sustain such losses had slowly ground down the US Eighth Army. General Mark Clark, UN commander, suspended all offensive operations involving more than one battalion -- a prohibition that held for the rest of the war. No major UN offensive followed Triangle Hill. In China, the outcome was celebrated as a victory. Qin Jiwei, commander of the 15th Corps, became a national hero and eventually rose to Minister of Defense. The 15th Corps itself was selected to become China's first airborne corps in 1961 and remains one of the most elite units in the Chinese military. The battle demonstrated a grim arithmetic: a force willing to accept massive casualties can defeat a technologically superior enemy if that enemy's tolerance for losses is lower.