Fighting across the 38th Parallel (Early 1951)
In January 1951, the Chinese and North Korean forces struck again in their 3rd Phase Offensive (also known as the Chinese Winter Offensive). The Chinese repeated their previous tactics of mostly night attacks, with a stealthy approach from positions some distance from the front, followed by a rush with overwhelming numbers, and using trumpets or gongs both for communication and to disorient their foes. Against this U.N. forces had no remedy, and their resistance crumbled; they retreated rapidly to the south (referred to by U.N. forces as the “bug-out”). Seoul was abandoned, and was captured by Communist forces on the 4 January 1951.

To add to the Eighth Army’s difficulties, General Walker was killed in an accident. He was replaced by a World War II airborne veteran, Lieutenant-General Matthew Ridgway, who took immediate steps to raise the morale and fighting spirit of the battered Eighth Army, which had fallen to low levels during its retreat. Nevertheless, the situation was so grim that MacArthur mentioned the use of atomic weapons against China, much to the alarm of America’s allies.

U.N. forces continued to retreat until they had reached a line south of Suwon in the west and Wonju in the center, and north of Samchok in the east, where the front stabilized. The PVA had outrun its supply line and was forced to recoil. The Chinese could not go beyond Seoul because they were at the end of their logistics supply line—all food and ammunition had to be carried at night on foot or bicycle from the Yalu River.

In late January, finding the lines in front of his forces were deserted, Ridgway ordered reconnaissance in force, which developed into a full-scale offensive, Operation Roundup. The operation was planned to proceed gradually, to make full use of the U.N.’s superiority in firepower on the ground and in the air; by the time Roundup was completed, in early February, U.N. forces had reached the Han River, and re-captured Wonju.

The Chinese struck back in mid-February with their Fourth Phase Offensive, from Hoengsong in the center against IX Corps positions around Chipyong-ni. A short but desperate siege there fought by units of the U.S. 2nd Infantry Division, including the French Battalion, broke up the offensive; in this action, the U.N. learned how to deal with Chinese offensive tactics and be able to stand their ground.

Roundup was followed in the last two weeks of February 1951,with Operation Killer, by a revitalized Eighth Army, restored by Ridgway to fighting trim. This was a full-scale offensive across the front, again staged to maximize firepower and with the aim of destroying as much of the PVA and NKPA as possible. By the end of Killer, I Corps had re-occupied all territory south of the Han, while IX Corps had captured Hoengsong.

On 7th March, 1951, the Eighth Army pushed forward again, in Operation Ripper, and on the 14th expelled the North Korean and Chinese troops from Seoul, the fourth time in a year the city had changed hands. Seoul was in utter ruins; its prewar population of 1.5 million had dropped to 200,000, with severe food shortages.[27]

MacArthur was removed from command by President Truman on April 11, 1951, for insubordination, setting off a firestorm of protest back in the States. The new supreme commander was Ridgway, who had managed to regroup U.N. forces for the series of effective counter-offensives. Command of Eighth Army passed to General James Van Fleet.

Chinese soldier killed by US Marines.A further series of attacks slowly drove back the Communist forces, such as Operations Courageous and Tomahawk, a combined ground- and air-assault to trap Communist forces between Kaesong and Seoul. U.N. forces continued to advance until they reached Line Kansas, some miles north of the 38th parallel.

The Chinese were far from beaten, however; In April 1951 they launched their Fifth Phase Offensive, (also called the Chinese Spring Offensive) This was a major effort, involving three Field Armies (up to 700,000 men). The main blow fell on I Corps, but fierce resistance in battles at the Imjin River and Kapyong, blunted its impetus, and the Chinese were halted at a defensive line north of Seoul (referred to as the No-Name Line).

A further Communist offensive in the east against ROK and X Corps on the 15 May also made initial gains, but by the 20th the attack had ground to a halt. Eighth Army counterattacked and by the end of May had regained Line Kansas.

The decision by U.N. forces to halt at Line Kansas, just north of the 38th Parallel, and not to persist in offensive action into North Korea, ushered in the period of stalemate which typified the remainder of the conflict.