Pusan Perimeter Defense and Breakout
The battle for the Pusan Perimeter was one of history’s great mobile defensive operations. It was certainly the longest, largest, and most complex mobile defense in U.S. military history. On June 25, 1950, Korean People’s Army (KPA, North Korean Army) forces invaded the Republic of Korea (ROK, South Korea), unleashing the Korean War (1950–1953). The goal of Kim Il Sung, leader of the Democratic People’s Republic of Korea (DPRK, North Korea), was to conquer the People’s Republic of Korea (ROK, South Korea) in a matter of weeks before the United States, should it choose to intervene, could influence the outcome.
U.S. president Harry S. Truman committed U.S. forces, and on June 27, while the Soviet Union was boycotting its sessions, the Security Council of the United Nations (UN) voted to ask UN member states to furnish “every assistance” to South Korea. On June 30 Truman authorized U.S. Far Eastern commander General Douglas MacArthur to employ all available forces in Korea.The four U.S. divisions in Japan comprising Lieutenant General Walton H. Walker’s Eighth Army were all below authorized strength. Training levels were low, equipment was worn and dated from World War II (1939–1945), and there were serious shortages in weapons. By cannibalizing the 7th Division though, MacArthur was able to get first the 24th Infantry Division and then the 25th Infantry Division and 1st Cavalry Division to Korea within two weeks.
The war was going badly for the outnumbered and outgunned South Korean forces and their 500 U.S. military advisers. Seoul fell on June 28, and South Korean forces were forced to abandon most of their equipment north of the Han River when bridges on the southern edge of that city were blown prematurely. On July 5 U.S. Task Force Smith went into battle at Osan, 50 miles south of Seoul. Numbering only 540 U.S. troops, the task force was expected to stop an entire KPA division spearheaded by T-34 tanks but was speedily overwhelmed. Meanwhile, a United Nations Command (UNC) came into being. Washington insisted on a U.S. commander, and on July 10 Truman appointed MacArthur to head the new UNC.
U.S. troops did not perform well initially. Lack of training as well as faulty equipment and shortages impacted morale and fighting ability. Difficult terrain, primitive logistics, poor communication, and refugees choking the roads probably did more to delay the KPA advance than did American infantry. From the Battle of Osan, South Korean and U.S. 24th Division forces suffered an unbroken string of reverses: Chobnan on July 6–8, Chobngju on July 10, Chochiwobn on July 11–12, the Kubm River on July 15–16, and Taejobn on July 19–20. On July 25 the 1st Cavalry Division was forced to yield Yongdong. Slowly but surely the defenders were being driven back toward the South Korean port of Pusan.
Walker’s mission was to trade space for time to build up his forces and hold until the UNC could build up its strength. By the end of July, however, the Eighth Army was out of space, and on July 29 Walker issued his famous “Stand or Die” order. Holding Pusan was critical, but if Walker’s forces withdrew too far they would have insufficient depth in which to maneuver and mass forces for an eventual breakout. Walker ordered his forces behind the Naktong River and by August 4 had established what became known as the Pusan Perimeter (also known as the Naktong Perimeter), which consisted of a rectangle, approximately 100 by 50 miles, in the southeastern corner of Korea around Pusan.
Over the next month the Eighth Army was reinforced with the 5th Regimental Combat Team (RCT), the 1st Marine Provisional Brigade, regiments of the 2nd Infantry Division, and the British 27th Infantry Brigade. Walker also had the five surviving Republic of Korea Army (ROKA, South Korean Army) divisions. On the west his defensive line ran along the Naktong River except for the southernmost 15 miles, where the river turned east away from the line. The northern boundary ran through the mountains from Naktong-ni to Yonngdong on the east coast and the sea.
Walker enjoyed the advantage of interior lines and an effective logistics network. Pusan was the key. Korea’s chief seaport, it boasted modern facilities capable of handling 30 oceangoing vessels simultaneously with a daily discharge capacity of up to 45,000 tons (during the campaign the daily average was about 28,000 tons). Walker also had the advantage of rail lines linking Pusan with Miryang, Taegu, and Pohang.
Walker positioned his U.S. divisions along the Naktong. The 25th Infantry Division was located in the south, the 24th Infantry Division was in the center, and the 1st Cavalry Division was to its north. The ROKA 1st Division held the north until the line turned to the east.Across the northern flank of the line the ROKA 6th Division held the western portion, the 8th Division and Capital divisions held the center, and the 3rd Division held the eastern end. U.S. Army doctrine called for an infantry division to hold no more than a 9-mile-wide front, but along the Pusan Perimeter frontages ran 20–40 miles.
By mid-August, Walker could call on more than 500 tanks, a 5 to 1 advantage over the KPA. Walker also had the U.S. Navy and the U.S. Air Force, key elements in the ultimate victory. U.S. Navy ships close offshore provided accurate and highly effective gunfire support on the perimeter’s flanks. The U.S. Fifth Air Force enjoyed complete air supremacy, meaning that Walker could move assets within the perimeter without regard to cover and concealment. This enhanced the UNC’s mobility advantage, while the KPA was also prey to regular air attack and was forced to move largely at night.
Initially, 11 KPA divisions, commanded by Lieutenant General Kang Kon, faced UNC forces. From south to north along the Naktong they were the 6th (with the attached 83rd Motorcycle Regiment), 4th, 3rd, 2nd, 15th, and 1st divisions. In the north from west to east the KPA deployed its 13th, 8th, 12th, and 5th divisions and the 766th Independent Infantry Regiment. The bulk of the 105th Armored Division remained in reserve. In mid-August elements of the newly formed KPA 7th Division entered the southern end of the line north of the 6th Division, and the 9th Division and elements of the 10th Division joined the line south and north, respectively, of the 2nd Division. While intelligence estimates at the time gave a different picture, the UNC actually held a slight numerical advantage of some 92,000 to 70,000 men, although many of Walker’s troops were manning the logistics infrastructure.
Between August 5 and September 9 KPA forces attacked the Pusan Perimeter along four widely separated axes, all of which followed natural approach corridors. The southern route ran through Chindong-ni to Masan, 30 miles from Pusan. A northern corridor extended from the Naktong to Miryang. Another route ran through Taegu, the largest city within the perimeter and a vital crossroads. The final avenue ran south from Angang-ni through Kyongju to Pusan.
KPA forces had the initiative and could concentrate superior numbers at the selected points of attack, while Walker was obliged to spread his troops across the entire front, shifting individual regiments as required. None of his divisional commanders had ever commanded divisions in combat, so Walker had to train them on the job.On August 9 Walker launched a division-sized limited-objective attack (Task Force Kean) on his southern flank, but stubborn KPA resistance blocked it. Between August 5 and 18 the KPA launched a series of attacks along the other three avenues. Although the attackers registered gains, all the drives were halted thanks to Walker’s skillful shifting of assets and the arrival of reinforcements.
On August 27 the KPA launched its second offensive over the same avenues. This time the attacks were well coordinated and hit simultaneously. By September 3 Walker was fighting in five different locations at the same time. American casualties during the first two weeks of September 1950 were the heaviest of the war, yet Walker was able to shift his reserves inside the ever-shrinking perimeter and prevent any major breakthroughs. On September 9 General Kang Kon was killed in a land mine explosion and was replaced by Genereal Kim Chaek as commander of KPA forces. On September 12 the KPA offensive reached its culminating point and stalled. The Eighth Army now numbered about 84,500 troops, while the ROKA numbered 72,000 troops.
When the U.S. X Corps of two divisions landed at the port of Inchon on September 15, well behind the bulk of the KPA, UNC forces were still locked in battle along the Pusan Perimeter. The next day the Eighth Army began its attempt to break out. Hampered by insufficient river-crossing equipment and a severe shortage of artillery ammunition, the breakout was not achieved until September 23, when KPA forces began a withdrawal. The allies followed, and on the morning of September 27 just north of Osan, lead elements of the Eighth Army linked up with the U.S. 31st Infantry Regiment of the 7th Infantry Division of X Corps.
The battle for the Pusan Perimeter was over. The single biggest flaw for the KPA was its inability to achieve the necessary mass at a decisive point. Its only hope had been to achieve overwhelming mass at one point, punch through the thinly held UNC lines, and drive on Pusan, but the KPA had failed to do this. Only 20,000 to 30,000 of KPA troops along the Pusan Perimeter ever returned to North Korea. The defenders paid a high price as well. Between July 5 and September 16, Eighth Army casualties totaled 4,280 killed in action, 12,377 wounded, 2,107 missing, and 401 confirmed captured.
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