With Lieutenant-General Matthew Ridgway assuming the command of the US Eighth Army on 26 December, the PVA and the KPA launched their Third Phase Offensive (also known as the "Chinese New Year's Offensive") on New Year's Eve of 1951. Utilizing night attacks in which UN Command fighting positions were encircled and then assaulted by numerically superior troops who had the element of surprise. The attacks were accompanied by loud trumpets and gongs, which fulfilled the double purpose of facilitating tactical communication and mentally disorienting the enemy. UN forces initially had no familiarity with this tactic, and as a result some soldiers "bugged out," abandoning their weapons and retreating to the south. The Chinese New Year's Offensive overwhelmed UN forces, allowing the PVA and KPA to conquer Seoul for the second time on 4 January 1951.
B-26 Invaders bomb logistics depots in Wonsan, North Korea, 1951
These setbacks prompted General MacArthur to consider using nuclear weapons against the Chinese or North Korean interiors, intending radioactive fallout zones would interrupt the Chinese supply chains. However, upon the arrival of the charismatic General Ridgway, the esprit de corps of the bloodied Eighth Army immediately began to revive.
UN forces retreated to Suwon in the west, Wonju in the center, and the territory north of Samcheok in the east, where the battlefront stabilized and held. The PVA had outrun its logistics capability and thus was forced to recoil from pressing the attack beyond Seoul; food, ammunition, and materiel were carried nightly, on foot and bicycle, from the border at the Yalu River to the three battle lines. In late January, upon finding that the PVA had abandoned their battle lines, General Ridgway ordered a reconnaissance-in-force, which became Operation Roundup (5 February 1951). A full-scale X Corps advance gradually proceeded while fully exploiting the UN Command's air superiority, concluded with the UN reaching the Han River and recapturing Wonju near Seoul.
In mid-February, the PVA counterattacked with the Fourth Phase Offensive and achieved initial victory at Hoengseong. But the offensive was soon blunted by the IX Corps positions at Chipyong-ni in the center. Units of the US 2nd Infantry Division and the French Battalion fought a short but desperate battle that broke the attack's momentum. The battle is sometimes known as the Gettysburg of the Korean War. The battle saw 5,600 Korean, American and French defeat a numerically superior Chinese force. Surrounded on all sides, the US 2nd Infantry Division Warrior Division's 23rd Regimental Combat Team with an attached French Battalion was hemmed in by more than 25,000 Chinese Communist Forces. United Nations Forces had previously retreated in the face of large Communist forces instead of getting cut off, but this time they stood and fought. The allies fought at odds of roughly 15 to 1.
In the last two weeks of February 1951, Operation Roundup was followed by Operation Killer, carried out by the revitalized Eighth Army. It was a full-scale, battlefront-length attack staged for maximum exploitation of firepower to kill as many KPA and PVA troops as possible. Operation Killer concluded with I Corps re-occupying the territory south of the Han River, and IX Corps capturing Hoengseong. On 7 March 1951, the Eighth Army attacked with Operation Ripper, expelling the PVA and the KPA from Seoul on 14 March 1951. This was the city's fourth conquest in a years' time, leaving it a ruin; the 1.5 million pre-war population was down to 200,000, and people were suffering from severe food shortages.