North Korean People's Army

The North Korean People's Army was the principal military force behind the June 1950 invasion of South Korea. Its rapid advance overwhelmed poorly prepared defenders and brought Seoul under North Korean control, but the successful Inchon landing and the breakout from the Pusan Perimeter turned the campaign against it, trapping more than half of the North Korean Army by late September.

Invasion and Early Advance

On June 27, headlines reported North Korean tanks sweeping into Seoul as the South Korean government fled. From Pyongyang, Premier Kim Il Sung vowed to crush South Korea swiftly. The invasion placed the North Korean People's Army at the center of a war that moved quickly from an attack on the South to a crisis demanding an American and United Nations response.

The first American ground troops entered combat near Osan on July 5: 256 men from the 24th Infantry Division. They had been rushed from Japan without adequate preparation, and they and their South Korean allies faced a disciplined enemy advancing in large numbers with Russian T-34 tanks. On July 6, General Omar Bradley estimated that 90,000 North Koreans were involved in the operation, compared with about 10,000 American troops and 25,000 South Korean troops. In many engagements, the defenders were outnumbered three to one or more; their available weapons could not reliably stop the tanks.

Pressure on the Defenders

The North Korean advance drove American and South Korean forces into a sustained retreat. The American units, many composed of young draftees without combat experience, had arrived from garrison duty in Japan and were inadequately equipped for the scale and speed of the attack. The South Korean forces were also short of arms capable of slowing the tanks. The difference in numbers and equipment helped turn early encounters into a struggle to prevent retreat from becoming a rout.

By the first week of July, the military situation was serious enough that Douglas MacArthur requested 30,000 additional American ground troops. On July 9, he called for twice that number, saying four more divisions were urgently needed. The scale of those requests reflected how sharply the North Korean offensive had tilted the balance in the early weeks of the war.

Reversal at Inchon

The amphibious landing at Inchon began on September 15 and took the North Korean forces by surprise. The invasion force comprised 262 ships and 70,000 men of the U.S. Tenth Corps, with the 1st Marine Division leading the assault. Inchon fell in little more than a day, and Seoul was retaken within eleven days. At the same time, General Walton Walker's Eighth Army broke out of the Pusan Perimeter and advanced north.

The combined pressure produced a decisive reversal. By September 27, more than half of the North Korean Army had been trapped in a large pincer movement. On October 1, United Nations forces reached the 38th parallel, and South Korea was under United Nations control. The army that had advanced rapidly toward Seoul was now confronted with the collapse of its gains and the loss of a large part of its force.

Significance in the Campaign

The North Korean People's Army's early superiority made the invasion an immediate emergency for South Korea and a test of whether outside forces could hold the line. Its advance shaped the decision to commit American troops, while the conditions facing those troops underscored the imbalance they initially confronted. The Inchon landing and the Eighth Army's breakout then transformed the conflict: the central military question shifted from whether the defenders could survive to whether the war would continue north of the 38th parallel.