Invasion and counterinvasion, 1950–51

South to Pusan

In early 1949 Kim Il-sung pressed his case with Soviet leader Joseph Stalin that the time had come for a conventional invasion of the South. Stalin refused, concerned about the relative unpreparedness of the North Korean armed forces and about possible U.S. involvement. In the course of the next year, the communist leadership built the KPA into a formidable offensive force modeled after a Soviet mechanized army. The Chinese released Korean veterans from the People’s Liberation Army, while the Soviets provided armaments. By 1950 the North Koreans enjoyed substantial advantages over the South in every category of equipment. After another Kim visit to Moscow in March–April 1950, Stalin approved an invasion.

In the predawn hours of June 25, the North Koreans struck across the 38th parallel behind a thunderous artillery barrage. The principal offensive, conducted by the KPA I Corps (53,000 men), drove across the Imjin River toward Seoul. The II Corps (54,000 soldiers) attacked along two widely separated axes, one through the cities of Ch’unch’ŏn and Inje to Hongch’ŏn and the other down the east coast road toward Kangnŭng. The KPA entered Seoul in the afternoon of June 28, but the North Koreans did not accomplish their goal of a quick surrender by the Rhee government and the disintegration of the South Korean army. Instead, remnants of the Seoul-area ROKA forces formed a defensive line south of the Han River, and on the east coast road ROKA units gave ground in good order. Still, if the South was to stave off collapse, it would need help—from the U.S. armed forces.

Truman’s initial response was to order MacArthur to transfer munitions to the ROKA and to use air cover to protect the evacuation of U.S. citizens. Instead of pressing for a congressional declaration of war, which he regarded as too alarmist and time-consuming when time was of the essence, Truman went to the United Nations for sanction. Under U.S. guidance, the UN called for the invasion to halt (June 25), then for the UN member states to provide military assistance to the ROK (June 27). By charter the Security Council considered and passed the resolutions, which could have been vetoed by a permanent member such as the Soviet Union. The Soviets, however, were boycotting the Council over the issue of admitting communist China to the UN. Congressional and public opinion in the United States, meanwhile, supported military intervention without significant dissent.

Having demonstrated its political will, the Truman administration faced the unhappy truth that it did not have much effective military power to meet the invasion. MacArthur secured the commitment of three divisions from Japan, but U.S. ground forces only expanded the scope of defeat. For almost eight weeks, near Osan, along the Kum River, through Taejŏn, and south to Taegu, U.S. soldiers fought and died—and some fled. Weakened by inadequate weapons, limited numbers, and uncertain leadership, U.S. troops were frequently beset by streams of refugees fleeing south, which increased the threat of guerrilla infiltration. These conditions produced horrifying attacks on Korean civilians. From late June to mid-July, South Korean paramilitary forces massacred thousands of civilians at Taejŏn, a war crime that was attributed to the North Koreans by South Korean and U.S. authorities for half a century. During the last week in July, U.S. troops and aircraft fired on refugees at a railroad viaduct near the hamlet of Nogun-ri, west of the Naktong River, killing hundreds.

It was not until the first weeks of August that the United Nations Command, or UNC, as MacArthur’s theatre forces had been redesignated, started to slow the North Koreans. The Eighth Army, commanded by Lieutenant General Walton H. Walker, one of the best corps commanders in Europe in 1944–45, and the ROKA, led by Major General Chung Il-kwon, rallied and fought back with more success. Supplies came through the port at Pusan, where the Eighth Army’s logistics system depended on Korean and Japanese technicians and on thousands of Korean labourers. To stop the North Koreans’ tanks and supporting artillery and infantry, Walker brought in Sherman and Pershing medium tanks, rocket launchers, artillery pieces, antiaircraft guns, and, most important of all, close-air-support aircraft. The Fifth Air Force attacked forward units of the KPA with World War II-era P-51 Mustangs, new jet-powered F-80s and F-84s, and even B-26 and B-29 bombers. U.S. Marine Corps squadrons, embarked on navy light carriers, were capable of flying anywhere along the front in quick response to requests from ground forces, and on the east coast the U.S. Navy’s cruisers and destroyers became a seagoing heavy artillery for the ROK I Corps. Meanwhile, fresh U.S. Army and Marine Corps units began to arrive, supplemented by a British Commonwealth brigade. In the same period, the ROKA, which had shrunk to half its prewar strength through deaths, surrenders, a few defections, and substantial desertions, began to bring its ranks back up with reservists, student volunteers, and men impressed from cities’ streets as the South Koreans fell back.

Korean War events

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Inchon landing

September 15, 1950 - September 26, 1950

Battle of the Chosin Reservoir

November 1950 - December 1950

Battle of Kapyong

April 23, 1951 - April 25, 1951

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Concerned that the shift of combat power toward the UNC would continue into September, the field commander of the KPA, General Kim Chaek, ordered an advance against the Naktong River–Taegu–Yŏngdŏk line, soon to become famous as the “Pusan Perimeter.” The major effort was a double envelopment of Taegu, supplemented by drives toward Masan and P’ohang, the southwestern and northeastern coastal anchors of the perimeter. None reached significant objectives. At the Battle of Tabu-dong (August 18–26), the ROK 1st Division and the U.S. 27th Regimental Combat Team defeated the North Koreans’ main armoured thrust toward Taegu. By September 12 the KPA, its two corps reduced to 60,000 men and its tank forces destroyed, had been driven back in most places west of the Naktong and well away from Taegu and P’ohang. At that moment the entire strategic balance of the war was shifted by the sudden appearance of the X Corps at Inch’ŏn.