The Korean War is notable for two of the most significant intelligence failures in U.S. military history: the failure to anticipate the North Korean invasion of South Korea in 1950 and the failure to foresee the massive Chinese intervention in the war in November 1950. These failures were the result of several factors including the post-WWII dismantling of the wartime intelligence structure, severe pressure to reduce defense budgets, the desire to focus all possible intelligence resources on the Soviet Union, and the failure to question the mistaken assumption that all communist governments acted only at the direction of the Soviet Union.

Encyclopedia of US Intelligence

ENCYCLOPEDIA OF U.S. INTELLIGENCE: THE KOREAN WAR

Abstract

The Korean War is notable for two of the most significant intelligence failures in U.S. military history: the failure to anticipate the North Korean invasion of South Korea in 1950 and the failure to foresee the massive Chinese intervention in the war in November 1950. These failures were the result of several factors including the post-WWII dismantling of the wartime intelligence structure, severe pressure to reduce defense budgets, the desire to focus all possible intelligence resources on the Soviet Union, and the failure to question the mistaken assumption that all communist governments acted only at the direction of the Soviet Union.

Keywords

Korean War, North Korea, South Korea, Gen. Douglas MacArthur, , Maj Gen Charles A. Willoughby, Far East Command (FECOM), Korea Military Assistance Group (KMAG), Korea Liaison Office (KLO), Armed Forces Security Agency (AFSA), Army Security Agency (ASA)

Introduction

The Korean War (1950-1953) was a seminal event in the Cold War conflict between the United States and the Soviet Union and a significant catalyst for the creation of the modern American intelligence establishment. While the original purpose of the war was the political reunification of North and South Korea, the growing ideological rivalry between the United States and the Soviet Union dominated the conflict from the start and ensured that its effects would be felt far beyond the Korean peninsula. The fact that the war occurred at all was a failure of intelligence on both sides of the Cold War divide. The United States, the Soviet Union, and the People’s Republic of China did not seek war in Korea, but a series of intelligence failures, misunderstandings, mistaken assumptions and miscommunications both enabled and shaped the conflict. North and South Korea each sought war as a means of unifying the country under their own government, but neither they nor their patrons anticipated the actual course of the conflict. Five years of declining U.S. defense budgets and neglect of the nation’s intelligence gathering capabilities had left American military and civilian decision-makers ill prepared to manage the demands of the post-World War II contest with the Soviet Union. The war in Korea forcefully demonstrated the folly of conducting foreign policy with inadequate intelligence, sparked a rapid and sustained expansion of the nation’s intelligence apparatus, and hastened the implementation of the highly-militarized containment strategy that had been recommended in National Security Council Report 68 (NSC 68).

The Roots of War: Korea Before 1945

The Korean War began before dawn on 25 Jun, 1950 when North Korean armed forces invaded South Korea in an effort to reunify the peninsula. Thirty-seven months of bitter fighting killed more than two million people and laid waste to huge sections of the country, but failed to reunify the peninsula. While the war was initiated by North Korea, the nascent Cold War competition between the United States and the Soviet Union dominated the conflict. As had been the case so often in Korean history, the peninsula was a battleground for great power rivalries.
Although nominally independent since the 14th century, Korea had for centuries been the object of competition between Japan, China, and Russia. But the decline of China and the Japanese victory in the Russo-Japanese War of 1904-1905 left Japan predominant. Free to do as they wished, the Japanese made Korea a protectorate in 1905 and formally annexed the peninsula in 1910, imposing a contested and brutal occupation that would last until the Japanese surrender in 1945. Japan’s defeat brought a sudden end to Japanese rule in Korea, but to the intense disappointment and anger of Koreans it did not bring political freedom. Fearing that the long years of Japanese occupation had impaired Korea’s ability to exercise full sovereignty, the victorious allied powers were reluctant to grant a liberated Korea political freedom. But the allies could not agree on a plan for overseeing Korea, and in 1945 the sudden surrender of Japan left them unprepared.

A Nation Divided: Korea from 1945-1950

Prior to the Japanese surrender U. S. officials had not intended to occupy Korea. But the Soviet invasion of Manchuria and Korea in August 1945 caused the Americans to reconsider their policy toward Korea. Soviet and American relations were deteriorating and although Korea held no particular strategic interest for the United States, American planners did not want to see the peninsula occupied and dominated by the USSR. American officials hastily drew up a plan to divide Korea into U.S. and Soviet occupation zones using the 38th parallel – a line with no historical, political or geographic significance – as the dividing line and the Soviets quickly agreed. The Koreans were not consulted.
The division of the country at the 38th parallel split Korea unevenly and severely disrupted the economies of both occupation zones. The largely agrarian south contained the capital and largest city, Seoul, and produced food for the north, while the more industrialized north produced manufactured goods and raw materials for the south. South Korea was smaller than North Korea (37,000 square miles in the south against 48,000 square miles in the north) but had a much greater population (21 million persons in the south against 9 million in the north). The north, however, had a better-educated population, and contained the majority of the country’s coal, mineral deposits and electrical generating plants. (1)
U.S. and Soviet occupation forces installed military governments and began the process of creating civilian government institutions. At the time, neither the United States nor the Soviet Union anticipated or intended that the division of Korea would last for decades. The Russians quickly established a provisional North Korean government and selected a former anti-Japanese resistance fighter named Kim Il Sung to lead it.
In the south the United States struggled to make sense of a confusing and deteriorating political situation. American occupation forces were unprepared for their complex task and were largely ignorant of Korean history, culture, and language. U.S. intelligence capabilities in Korea were remarkably poor. With U.S. Government attention focused on the occupations of Germany and Japan, little thought had been given to the occupation of Korea. As a result, the command received virtually no strategic guidance on U.S. interests in Korea and received few, if any, of the resources necessary to conduct an effective administration. U.S. forces in Korea were insufficient in numbers, training, and specialized skills, especially Korean language skills. Intelligence officers assigned to the Korean occupation were not Korean specialists and they struggled to understand the chaotic political situation in South Korea.
In those post-war years U.S. intelligence shortcomings were not confined to Korea. American intelligence capabilities throughout the Far East and in Washington were marked by poor collection, processing, analysis, and reporting practices and procedures. (2)
For U.S. forces in Korea, little intelligence help was available from other sources within the government, as the nation’s rapidly shrinking intelligence apparatus was focused almost entirely on the Soviet Union. Lacking effective intelligence, U.S. military administrators made several key missteps which damaged their credibility and contributed to the unrest which rocked South Korea. Although Korean exiles had established a provisional Korean government in China during the long years of Japanese occupation, American occupation authorities refused to recognize it, fearing that it was aligned with the communists. Worse, the Americans initially kept Japanese occupation officials, including the hated security forces, in their positions, which damaged the legitimacy of the occupation administration. While US-military authorities soon delegated most day-to-day administrative workings of government to Korean administrators the US effort remained tainted.
During this period U.S. concern over the expansionist policies of the Soviet Union prompted a reappraisal of Korea’s strategic importance. Both U.S. and Soviet officials recognized that Korea was critical to any attempt to dominate Japan, which both nations prized. Since neither nation was willing to risk a unified Korea aligned with its ideological opponent, no serious effort was made by either the U.S. or the Soviet Union to reunify Korea.
In 1947 the frustrated Americans unilaterally referred the matter to the United Nations with a proposal for UN-supervised elections to be followed by Korean independence and the withdrawal of U.S. and Soviet occupation troops. The UN General Assembly approved the proposal, but the Soviets and the North Koreans refused to allow elections and left-wing parties in the south refused to participate. South Korean voters elected a right-wing anti-communist government which later elected the former exile and ardent anti-communist Syngman Rhee as Korea’s first president. On Aug 15, 1948 the Republic of Korea (South Korea) was formally established. On 8 September 1948 the Soviet Union responded by proclaiming the existence of the Democratic People’s Republic of Korea (North Korea). In December 1948 the United Nations General Assembly recognized the Republic of Korea (ROK) as the sole legal government of Korea.
Thus, by the end of 1948 the “temporary” division of Korea had resulted in the creation of two ideologically opposed states, backed by opposing superpowers, each committed to re-unifying the country under its own system. From 1948 until June of 1950 the two Koreas sparred with verbal threats, cross border raids and increasingly bloody border skirmishes using military equipment provided by their superpower backers. In addition, North Korea instigated and supported a large-scale communist insurgency in the South, which the ROK suppressed ruthlessly. Between 1946 and 1950 more than 100,000 South Koreans were killed. (3)
During this period U.S. policy towards South Korea was ambiguous. Relations with the Soviet Union continued to deteriorate as crises in Turkey and Greece prompted President Harry S Truman to announce the Truman Doctrine, promising support for free peoples battling communist takeover attempts. Although the U.S. was unwilling to cede South Korea to the Soviet Union, U. S. support for the Rhee’s regime was tempered by American unease with Rhee’s program of political repression. In the end the United States determined to develop South Korea into an independent state that could stand against the communist North.
But U.S efforts to assist South Korea were severely limited by financial constraints. Under severe Congressional and public pressure to balance the federal budget and keep taxes low, the administration lacked the resources to meet its growing global commitments and military officials in Washington urged the withdrawal of the 40,000 American occupation troops in Korea. Despite a growing recognition among American policymakers that Korea was strategically important and against Rhee’s pleas for U.S. forces to remain, U.S. occupation troops were withdrawn in 1949, a year after the last Soviet troops had left North Korea. The U.S. military presence in Korea was limited to a 500-man training contingent, the Korean Military Assistance group (KMAG). The U.S. decision to withdraw its occupation forces was influenced by the success of the ROK counter-insurgency campaign, the cost of maintaining the troops in Korea, and the withdrawal of Soviet forces.

Far East Command (FECOM) Intelligence Activities Before June 1950:

Between the end of World War II and the beginning of the Korean War, the successful wartime U. S. intelligence organization had been largely dismantled. From a peak of 12 million persons in 1945, the U. S. military had been reduced to 1.6 million by 1947. Defense spending had been slashed from $81 billion in 1945 to $13 billion in 1947. Intelligence organizations had suffered proportionally. Within Korea U.S. intelligence activities were chronically under-resourced, lacked a strong centralizing organization, and suffered from deficient leadership and poor coordination among regional commands. (2)
While U.S. occupation troops were in Korea, intelligence operations were the responsibility of General Douglas MacArthur’s Far East Command (FECOM). MacArthur’s Intelligence Chief (G-2) was Major General Charles A. Willoughby, who also served as the G-2 for MacArthur’s Supreme Commander Allied Powers (SCAP) organization. Willoughby had served as MacArthur’s Intelligence Chief throughout World War II, where he had acquired a reputation for slanting his intelligence reports to match MacArthur’s predetermined opinions. This was particularly unfortunate as MacArthur was famously loath to change his opinions, regardless of new information that might become available. (4) Between FECOM and SCAP Willoughby had more than 2,500 intelligence personnel under his command, but these units were directed almost entirely to supporting the occupation of Japan. FECOM was proficient at collecting information, but poor at analyzing it, primarily because it was poorly led. Willoughby and MacArthur both distrusted unconventional methods of intelligence gathering and consequently made no attempt to place agents in the north. As a result FECOM relied heavily on ROK sources. In general, FECOM’s intelligence organization was ineffective. (5)
SCAP G-2 focused on civil intelligence gathering and counterintelligence in Japan while FECOM G-2 focused on military intelligence matters in the Far East. Neither organization devoted significant resources to Korea. FECOM’s intelligence organization had just two Korean linguists. (6)
Following the withdrawal of US occupation troops in 1949, FECOM no longer was responsible for intelligence collection on the Korean peninsula. The residual US military command, the Korean Military Advisory Group (KMAG), had no intelligence collection capability. To fill the intelligence vacuum, in June 1949 FECOM established the Korean Liaison Office (KLO), whose primary responsibility was to monitor troop movements in the north and the activities of Communist guerillas operating in the south. (7).
Lacking technical collection capabilities, KLO was dependent on intelligence collected by the ROK or intelligence it could collect through human sources (HUMINT). In the year before the North Korean invasion, KLO infiltrated a small number of agents into North Korea. In June of 1950 KLO was reported to have had 16 agents operating in North Korea. KLO had some success reporting on North Korean military activities in southern portions of the DPRK, but was unable to infiltrate agents into the northern areas of the country and could not provide effective strategic intelligence or warnings. Since HUMINT reports could not usually be corroborated by other means they were mostly considered unreliable by officials in Tokyo and Washington. It was probably just as well. Many, if not most, of the KLO agents operating in North Korea disappeared almost immediately after the invasion, suggesting that they had been detected and likely co-opted by the North Koreans in the months before the attack. (2)
A similar HUMINT collection program was conducted by the Office of Special Investigations (OSI) of the Far East Air Forces (FEAF), a component of FECOM which retained considerable autonomy. FEAF’s focus was on Soviet military capabilities in the Far East, especially in Siberia. From 1945 until the withdrawal of American forces from South Korea in 1949 the intelligence staff of US Army Forces in Korea (USAFIK) also operated a small network of Korean agents in North Korea. (2)
The CIA in Korea Before June 1950:
In 1947 the Central Intelligence Agency (CIA) was formed from the remnants of the wartime Office of Strategic Services (OSS). But the fledgling agency had a small budget, no history, and little influence in Washington DC or Tokyo.
In the Far East the CIA had inherited the antipathy that MacArthur and Willoughby had felt for the OSS during the Pacific War, during which MacArthur had actively resisted OSS attempts to operate in his Southwest Pacific Theater. From Tokyo MacArthur was equally determined to control all of the intelligence that was transmitted from his theater to Washington and he refused to cooperate with the CIA, preferring to rely on Willoughby’s intelligence organization. MacArthur’s antagonism severely handicapped CIA operations in Korea as he refused to allow the Agency to operate an office on the peninsula. (5)
Until 1949 the CIA’s focus was on mainland China, and the Agency operated an office there. But the Communist victory in 1949 forced the CIA to relocate its operations and the Agency was permitted to open a small office at the U.S. Navy base in Yokosuka, Japan. In 1950 a six-person detachment of the CIA’s Office of Policy Coordination (OPC) arrived in Japan to act as liaison to the FECOM G-2 organization. FECOM cooperation with CIA remained minimal, however. (2)
Communications Intelligence in Korea: ASA, NSG, AFSS and AFSA
In the years between the end of WWII and the beginning of the Korean War U.S. communications intelligence (COMINT) underwent major structural and doctrinal changes. During this period communications intelligence collection and processing activities for FECOM were managed by the Army Security Agency Pacific (ASAPAC), a regional command of the Army Security Agency (ASA). ASA had been created in September 1945 when the Army’s Signals Security Agency (SSA) was reorganized. ASA was charged with collecting, processing and analyzing signals intelligence against the Soviet Union and later the People’s Republic of China and their allies or satellites. ASA operated four listening posts in the Far East: three in Japan and one in the Philippines, but, in accordance with ASA’s charter, their collection activities were focused almost exclusively on the Soviet Union. (2)
Worldwide, U.S. COMINT collection and processing resources were far short of requirements. U.S. COMINT collection priorities were set by the U.S. Communications Intelligence Board (USCIB) in Washington DC and not by theater commanders. One result was that cooperation between FECOM and ASA, including sharing of communications intercepts, was limited. (2)
The Navy and Air Force also operated small COMINT offices in Korea that were staffed and equipped for their peacetime tasks of monitoring Soviet military activities. These units were the Navy’s Communications Supplementary Activity (COMMSUPACT) and the Air Force Security Service (AFSS). In 1950 COMMSUPACT became the Naval Security Group (NSG). COMINT collection and processing efforts by the three service agencies were not integrated into the Far East Command’s intelligence structure and were not coordinated, resulting in a significant duplication of effort. (2)
In 1949 the Department of Defense created the Armed Forces Security Agency (AFSA) to direct the communications and electronic intelligence activities of the ASA, AFSS and COMMSUPACT.
But AFSA had little power and lacked the legal authority necessary to fulfill its mandate and was therefore ineffective. As a result, in Nov 1952 it was replaced by the newly-created national Security Agency (NSA). (8)

The Decision to Invade

Neither the United States nor the Soviet Union desired war in Korea, and as long as both superpowers maintained troops there military conflict was highly unlikely. But neither power wanted a permanent military presence in Korea and neither believed that the withdrawal of their forces would result in war. By June 1949 the Soviet Union and the United States had withdrawn their occupation forces, leaving behind two newly created military establishments.
In North Korea the Soviets left behind a well-equipped and well-trained army of 135,000 highly motivated soldiers armed with modern Soviet T-34 tanks, heavy artillery and an air force of 200 combat aircraft. More than half of the DPRK soldiers were combat veterans of the Chinese civil war. (9)
In South Korea the United States left behind a 95,000 man army, organized in eight divisions, of which only four were at full strength, and $40 million worth of small arms, machine guns, light artillery and trucks. But for a variety of reasons, including financial constraints, bureaucratic inertia, fear of a South Korean invasion of the north, and a mistaken assessment of the usefulness of armored vehicles, the U.S. did not provide the ROK with combat aircraft, tanks, or heavy artillery.
Under intense pressure to keep defense spending low, U.S. military aid to South Korea in 1949 was limited to $10.2 million which precluded the inclusion of tanks, aircraft and heavy artillery. In December 1949, however, following the departure of U. S. combat forces, the KMAG chief requested and received an additional $9.8 million worth of military aid for South Korea, including F-51 and F-6 combat aircraft. But virtually none of the additional equipment and none of the aircraft had been delivered by the time of the North Korean invasion. (10)
While KMAG advisers recognized the importance of combat aircraft, they wrongly believed that Korea’s mountainous terrain, narrow roads and many bridges made the country unsuitable for armored vehicles and they therefore refused to provide tanks to the ROK Army. Because they doubted the ability of DPRK tanks to penetrate far from the border, US advisers provided no modern anti-tank weapons to the ROK forces. U. S. advisers also over-estimated the capabilities of ROK armed forces. Before the war US advisers considered the ROK army “increasingly efficient” and believed – wrongly, as it turned out – that they were capable of defending the south against invasion by the North. In mid-June the CIA ranked the DPRK and ROK armies as equal in manpower, training, and leadership, with the DPRK having an advantage in armor, heavy artillery and aircraft. Less than two weeks before the invasion, the CIA reported that despite improvements the North Korean army still lacked the ability to overrun South Korea, in part because of the strong anti-communist attitudes in South Korea and the higher morale of the ROK forces. (11)
But the ROK forces suffered from poor leadership, serious maintenance problems, a near-total lack of spare parts, and a lack of ammunition. The DPRK forces were better equipped, more numerous and more experienced. (12)
Having failed in his efforts to reunify the peninsula through guerilla warfare, in March 1949 Kim il Sung visited Moscow and proposed an armed invasion of the south. The ever-cautious Stalin was reluctant to approve the plan, but agreed to supply $40 million in arms. Stalin hoped that the ROK would attack the North and the DPRK could then re-unify the peninsula using massive amounts of Soviet military assistance. (13)
By early 1950, though, following the withdrawal of U. S. occupation troops from South Korea, the victory of the Chinese Communists against the Nationalist Chinese and the stiffening of western resolve in Europe, Stalin had begun to reconsider. A North Korean invasion of South Korea would apply additional pressure to the United States and might weaken the western position in Europe. On Jan 17, 1950 Stalin gave Kim the go-ahead.
But while Stalin doubted that the Americans would intervene, he warned Kim that if the United States did enter the war the DPRK could not count on Soviet intervention and would have to depend on China for assistance. Kim then approached Mao with his plans. Mao tried to dissuade Kim, even though Stalin had already given his approval, because he believed that the timing was not favorable for China. Mao had hoped to secure the final defeat of the Nationalist forces on Formosa in 1950 and he knew that he lacked the military power to defeat the Nationalists and to support Kim. (Freidman/11)
But China needed Soviet aid, especially air and naval assistance, to defeat the Nationalist forces and Mao could not afford to oppose Kim’s plan once he knew that Stalin had approved it. Mao also felt a sense of obligation toward the Koreans who had provided tens of thousands of soldiers for his armies during the Chinese civil war. With the civil war now won, many of these soldiers were already returning to North Korea where they were strengthening the DPRK army. Mao assented to the Korean plan.
Stalin’s precise motives remain unclear, but some evidence exists that he secretly hoped for a strong American response to the DPRK attack as a means of tying down US forces, and diverting US attention from Europe. An added benefit would be increased hostility between the US and the PRC, which would weaken both parties. (3)

Invasion and the UN and US Response

At 4:00 AM on the morning of 25 Jun 1950, a devastating mortar and artillery barrage signaled the start of the North Korean invasion of South Korea. 90,000 DPRK soldiers surged forward in a carefully planned and skillfully executed attack. A deception campaign that had included a sharp rise in border incidents in the preceding weeks helped the attack achieve strategic and tactical surprise. (10)
Rhee’s outnumbered forces were caught unawares. While some isolated units did make determined stands, their lack of effective anti-tank weapons doomed their efforts. ROK defenses quickly crumbled. Within hours of the attack Rhee requested U.S. arms shipments, but U.S. officials were non-committal. (12)
The next day the United States requested a meeting of the United Nations Security Council, and by the evening of 26 June the Council had passed a resolution condemning the North Korean attack and calling for a withdrawal of North Korean forces. The Soviet Union missed an opportunity to veto the resolution because its delegate had been boycotting the Security Council since January 1950 over the UN’s failure to seat Communist China.
But the UN resolution did nothing to slow the DPRK forces, which were now advancing on a broad front against sporadic opposition. On 27 June, after two days of terrifying suspense for the South Koreans, President Truman promised immediate air and naval support to Korea and sent the U. S. Seventh Fleet to the Formosa Strait to discourage China and the Chinese Nationalists from launching cross-strait operations. China was particularly alarmed at the Seventh Fleet deployment, which seemed to tie the US tightly to the defense of Formosa. (12)
On 27 June the UN Security Council approved a resolution calling upon member nations to provide assistance to the Republic of Korea to repel the armed attack. During the course of the war more than twenty nations provided military forces or medical units including Great Britain, Canada, Australia, New Zealand, Belgium, Colombia, Ethiopia, France, Greece, India Luxembourg, the Netherlands, the Philippines, Sweden, Thailand, Turkey, South Africa, Denmark, and Norway.
On 28 June DPRK forces captured Seoul. Two days later MacArthur told Washington that only the introduction of U.S. ground forces could save South Korea.

The Failure of U.S. Intelligence to Foresee the Invasion

The failure to foresee the North Korean invasion of the South was one of the most significant intelligence failures in American military history. U.S. policymakers expressed total surprise at the North Korean attack and FECOM’s flatfooted response leaves little doubt that the invasion was unexpected. But if American policymakers in Washington and Tokyo were surprised, many Americans and South Koreans on the peninsula were not. Despite acute problems in collecting, processing and analyzing intelligence on North Korean intentions, a steady stream of reports warning of an impending invasion had been flowing from U.S. and ROK intelligence organizations for months.
In the month prior to the invasion intelligence reports from South Korea and the CIA accurately describe North Korean preparations for war including the removal of civilians from the border area, the restriction of all transport capabilities for military use only, and the movements of military units to the border area. On 20 Jun 1950 the CIA published a report which concluded that North Korea had the capability to invade the South at any time. (7)
Despite the steady flow of warnings, U.S. policymakers concluded that no attack was imminent for several reasons:
U.S. officials did not believe that North Korea would act without Soviet direction and they were convinced that the Soviet Union was not prepared for war with the United States. American analysts believed that a DPRK attack would only be conducted as part of a larger Soviet assault on the West, and they did not see indications of such an effort elsewhere. This mistaken belief – that the Soviet Union controlled all North Korean decision making – is the single factor which best explains the U.S. failure to anticipate the North Korean invasion of the South. (7)
U.S. officials did not believe that North Korea would risk war with the United States. In Tokyo, MacArthur and his staff refused to believe that any Asians would risk facing certain defeat by threatening American interests. (7)
U.S. officials did not trust ROK warnings. They believed that ROK officials were exaggerating the threat of invasion in order to obtain increased military aid from the U.S. Throughout the pre-war period officials in Tokyo and Washington consistently discounted intelligence reports that relied on ROK sources. This was especially unfortunate because U.S. collection capabilities in North Korea were poor and many organizations including the CIA, relied almost exclusively on ROK sources. (13)
Officials in Korea had become acclimated to DPRK hostile acts, military movements, and intelligence warnings that had not been followed by an invasion and did not want to overreact to the most recent warnings. This tendency was exacerbated by the DPRK’s deception campaign which included an escalation of guerilla attacks and border clashes in the months preceding the invasion. (13)
U.S. intelligence organizations did not have a clear picture of events and intentions in North Korea. Lack of intelligence resources crippled U.S. intelligence efforts in Korea between 1945 and June 1950. COMINT provided no warning of the N Korean invasion because the few American COMINT intercept facilities that were available in the Far East during summer 1950 were targeted almost exclusively against Soviet military radio circuits. Even within FECOM, until the invasion of the South, North Korea was considered a secondary intelligence target. HUMINT collection efforts in North Korea were made much more difficult by the paranoid police-state character of the North Korean regime and the removal of civilians from areas near the 38th parallel.

The American Intervention

The American decision to send combat forces to Korea represented a startling reversal of U. S. policy and was unforeseen by Stalin, Mao, Kim, and MacArthur. By every measure the United States was unprepared for war on the Korean peninsula. Through inattentiveness in the face of higher priorities and a failure to make their intentions clear the U.S. had failed to deter the North Korean invasion. But now that it had occurred Truman was determined to resist the North Korean action. He believed – mistakenly – that the invasion could only have been ordered from Moscow and was possibly the opening move in a concerted military push against the west. (12)
But Truman was angered by the blatant disregard the North Koreans and Soviets were displaying toward the norms of international behavior. His decision to intervene was also influenced by the apparent lack of direct Soviet or Chinese involvement in the invasion, by the unequivocal support of U. S. allies, and by widespread public support in the U.S.
On 30 June Truman ordered a naval blockade of Korea, ordered the Air Force into action against the North Koreans, and authorized MacArthur to employ U.S. ground forces. Within hours elements of MacArthur’s occupation forces, were en route from Japan to Korea. MacArthur understood that his untrained, ill-equipped occupation troops were not combat-ready, but there was no time for additional training or re-equipping. (12)
Following their capture of Seoul, North Korean forces paused for several days to regroup and re-arm, a delay which probably saved Pusan. (12) On 5 July, having resumed their advance, North Korean soldiers encountered American troops for the first time near Osan.
But the unprepared U.S troops could not halt the North Korean advance and by 5 August the surviving U.S. and South Korean forces had been driven into a shrinking toehold centered on the port of Pusan. U.S. and ROK troops established a defensive perimeter around Pusan, but they had too few troops to properly hold the 130-mile-long line, and the danger of a North Korean breakthrough was very real.
But the North Koreans were facing serious problems as well. UN air attacks were disrupting the North’s supply lines and ROK and U. S. blocking actions, although unable to halt the DPRK advance, had cost the North Koreans some 58,000 casualties between 25 June and early August. North Korean ranks were being filled with untrained recruits from the captured areas of the South, but in quality and quantity they could not make up for the loss of trained men. At the same time, UN forces were being strengthened by the quickening flow of reinforcements, including U.S. tanks and heavy artillery. By early August the UN defenders at Pusan actually outnumbered the North Korean attackers, although neither side seemed to realize it at the time. (12)

The Communist Failure to Foresee the American Response

The Soviet Union, China and North Korea neither wanted nor expected the United States to intervene militarily in Korea. But the ambiguity of U.S. policy in South Korea confused communist analysts, causing them to discount the possibility of U.S. intervention. (14) Stalin did not believe that the United States would enter the war because the U.S. had demonstrated little previous commitment to the defense of the ROK. U.S. policymakers had withdrawn American combat forces from South Korea over the objections of the ROK president, had failed to fully equip the ROK armed forces, and had declined to offer the ROK any sort of security guarantee. There was also an obvious lack of enthusiasm for Rhee’s regime in the United States and there was significant Congressional opposition to any further financial aid to South Korea. In January 1950 U.S. Secretary of State Dean Acheson had seemed to place South Korea outside of the U.S. defensive arc in a deliberately ambiguous speech to the National Press Club in which he suggested that if attacked the ROK could expect help from the United Nations rather than from the U.S. (3) Stalin was also aware of the extent of American defense budget cuts and the U.S. failure to respond militarily to the Communist Chinese victory over the Nationalists in 1949.
Kim also believed that his forces could defeat the South Koreans before the United States could respond. He had been convinced by southern communist leaders that up to 200,000 communist sympathizers in the south would rise up and assist his invasion force, a belief that turned out to be untrue. Kim told Stalin that his forces could defeat the south completely in less than 27 days, faster than the Americans could intervene. (12)

Inchon

From the first weeks of the conflict MacArthur had been planning an amphibious assault at Inchon on S. Korea’s Yellow Sea coast, 30 miles south of Seoul, as a means of out-flanking the invading North Korean forces. (12)
Inchon was an exceptionally unpromising site for an amphibious assault and MacArthur’s plan was originally opposed by everyone who heard it. The problem with Inchon was not with the concept of an amphibious assault or even its location – a large ground force landing there would be well-placed to cut off the North Korean army at Pusan by severing their supply lines – but rather was with the characteristics of the landing areas. For one thing, there were no actual beaches. The landings would have to be made at the bases of sea walls which rose as high as eight feet above the decks of the landing craft, forcing assault troops to use ladders to get ashore. Landing craft could only approach the sea walls at maximum high tide, which only occurred twice each month. At all other times the approaches to the shore were blocked by miles of mud flats. Tides at Inchon ranged from an average of 23 feet to a maximum of 33 feet. Landing ships would have to approach Inchon through a long, narrow channel that was protected by coastal artillery and a rugged little island called Wolmi-Do that would have to be captured prior to the main landing, thus ensuring that the North Korean defenders were alerted. (15)
But MacArthur argued that the obvious unsuitability of Inchon would convince the North Koreans that no landing would be attempted there and he ultimately convinced the Joint Chiefs of Staff to authorize the landings. On 15 September 1950 the First Marine Division went ashore at Inchon.
As MacArthur had predicted, the landing achieved complete surprise and U. S. casualties were light. Despite receiving explicit warnings from the Chinese that a landing at Inchon was possible, the North Koreans failed to establish an adequate defense. Although the location of the landing was an open secret in Japan and Pusan, the North Koreans had refused to believe that UN forces would land there. Within ten days of the landings the Marines recaptured Seoul, although at the expense of tremendous damage to the city.
At Pusan, the strengthening UN forces launched an offensive on 16 September and within days were driving the North Koreans northward. Trapped between the two UN forces, the already-weakened North Korean army collapsed with astonishing speed. Fewer than 40,000 stragglers made their way, without equipment, across the parallel into North Korea. (15)

Crossing the Parallel

Within weeks UN forces had driven the North Koreans north of the 38th parallel. Light-headed from the sudden turn of events, U.S. policymakers began to consider the merits of crossing the parallel and re-unifying Korea under the ROK government, an option that was in agreement with the re-stated UN goal of creating a united, independent and democratic Korea. (15)
U.S. officials feared that if UN forces simply pushed the North Koreans back across the parallel they would regroup, re-arm, and eventually launch another attack. There could not be a lasting peace in Korea, they felt, as long as the nation remained divided. In addition, a failure to re-unify the country when the opportunity was available would demoralize the South Koreans. US policymakers also believed that failing to punish the aggressor would encourage others to take similar actions in similar circumstances. Finally, US officials saw the unification of Korea as a method of “seizing the offensive,” in the Cold War and reversing a trend of Communist successes. (13)
U.S. officials were aware of the risk of Soviet or Chinese intervention, but still believing that the Soviets would not risk war with the United States over Korea, and convinced that the PRC would not act except under Soviet direction, they discounted the possibility of intervention and authorized MacArthur to move north of the 38th parallel to complete the destruction of the North Korean armed forces. To reduce the risk of Chinese or Soviet intervention, only ROK forces were to operate in provinces bordering China and the USSR. Air and naval attacks against Chinese or Russian territory were prohibited. (12)
ROK units crossed the 38th parallel on 1 Oct 1950. U.S .and allied troops followed a week later. On 19 Oct Pyongyang fell to UN forces and on 25 Oct ROK forces reached the Yalu River, the border between North Korea and China. On 24 Oct MacArthur ordered U.S. troops to enter the provinces bordering the PRC and the USSR, despite explicit orders from the Joint Chiefs of Staff prohibiting such movements. But the Chiefs, who may have believed that the danger of Soviet or Chinese intervention had passed, did not take action. (12)(13)(15)
By late October, however, Chinese intervention was already a fact.

The Chinese Intervene

Chinese officials viewed the UN advance with considerable alarm. Uncertain of U.S. intentions and fearful that U.S. naval deployments to the Straits of Formosa and the U.S. intervention in Korea were preparations for an invasion of China, PRC officials considered the presence of U.S. ground forces in North Korea as unacceptable. Immediately following the landings at Inchon PRC leaders began issuing a series of diplomatic warnings through the USSR, the UN and India to stop UN forces at the 38th parallel.
Americans officials did not recognize how threatened the Chinese felt and discounted the warnings. Believing that their policies posed no threat to legitimate Chinese interests, U.S. leaders assumed that PRC leaders would see things the same way. (12) Truman and Secretary of State Dean Acheson made repeated attempts to calm Chinese fears and convince Chinese leaders that the UN advance was not a threat to China. But the Chinese were also hearing a chorus of starkly belligerent comments from Rhee, U.S. officials outside of the administration, and from MacArthur, all advocating some form of UN military action against China. (4)
When UN forces approached the 38th parallel, Chinese foreign minister Chou-en-Lai issued an explicit warning through the Indian ambassador that if U.S. troops entered North Korea, China would intervene in the war. (3)
General MacArthur and U.S. officials in Washington believed that the warning was a form of political blackmail and should be ignored. But the Chinese weren’t bluffing. On 13 October, following ten days of internal discussion and consultation with the Soviets, Mao decided to intervene.
PRC forces first made contact with UN units on 25 October at On Jong, less than 40 miles south of the Yalu River. Chinese commanders were confident that their forces would prevail against the better-equipped Americans because they considered U.S. troops soft, inexperienced, and lacking political motivation. They also believed that US troops were untrained in night attacks, were tactically inflexible, were overly dependent on firepower, and were limited by their long cross-Pacific supply lines. (11)
For nearly a week the Chinese forces conducted a series of attacks against ROK and U.S. units, halting the UN advance, inflicting thousands of casualties and driving the leading UN units back. But by 5 November the Chinese had broken contact. U.S. officials in Tokyo and Washington interpreted the PRC disengagement as an indication that the PRC attack had failed. They refused to believe that the Chinese were intervening in force and MacArthur readied his forces to resume the offensive. (12)
On 25 November more than 250,000 PRC soldiers struck UN forces in a second-phase offensive. Despite the earlier PRC attacks, U.S. and ROK units were unprepared for the assault and were driven back in disorder. Chinese and North Korean forces recaptured Pyongyang on 5 Dec and by 31 Dec had forced the UN forces back across the Imjin River, just south of the 38th parallel.
Initially PRC commanders had planned to drive UN forces south to a line from Pyongyang to Wonsan, across the narrowest part of the Korean peninsula, where they believed that UN forces would make a defensive stand. But the rapid retreat of the UN forces raised the possibility that the Communist armies could push the UN troops off the peninsula entirely. (13)
Accordingly, on 31 December, PRC forces launched a third-phase offensive which quickly captured Seoul and drove as far as 70 miles into South Korea. But the PRC advance exposed the lengthy communist supply lines to devastating UN air attacks. By mid-Jan, 1951, the PRC drive south had stalled 40 miles south of Seoul.

The American Failure to Foresee PRC Intervention

The failure to recognize and prepare for the Chinese intervention in November 1950 is one of the greatest American military errors of the twentieth century. The failure is all the more perplexing because the Chinese made such strenuous efforts to warn the UN command and because of the many indications that were accurately reported by UN intelligence officers. China’s repeated warnings, the late October clashes between PRC and UN forces, and interrogations of Chinese prisoners of war convinced many analysts in Tokyo, Washington DC and allied capitals that the Chinese were preparing to intervene on a large scale. (13)
As early as September 1950, AFSA, based on analysis of Chinese civil communications, AFSA was reporting stated that the PRC had moved major military units from southern or central China to Manchuria. Throughout September and October AFSA noted continued movement of these and additional forces toward the North Korean border and messages in November 1950 showed Beijing in a state of emergency. (8)
But MacArthur and senior officials in Washington remained unconvinced. They continued to believe that the Soviet Union controlled North Korean and Chinese decision-making and they still saw no indication that the Soviets were willing to risk a wider war. They also believed that China would not risk intervention because Chinese forces lacked the training, experience and equipment to defeat American units and that China would not want to hurt its chances of taking its seat in the UN. (14)
Throughout the summer of 1950 CIA reports blended tactical warnings of PRC activity with strategic analysis that no indications existed of Soviet intentions to order PRC units to intervene. These analyses were based on the continuing misperception that Soviet priorities and orders would dictate North Korean and PRC actions. (7) A CIA analysis further concluded that the PRC would not intervene because their economy was failing, they were exhausted from their civil war, the government had not yet consolidated its domestic power base, and the Nationalist Chinese on Formosa still posed a threat. (16)
U.S. intelligence analysts had amassed considerable evidence that PRC forces were present in North Korea, including interrogations of captured Chinese soldiers. But the overall picture was far from clear, and the U.S. ability to recognize Chinese intentions was limited. FECOM was forced to rely on speculation concerning PRC intentions because it lacked the intelligence capability to answer critical questions. Photo-reconnaissance flights over Manchuria were prohibited, aerial surveillance of Korea was unproductive, HUMINT efforts were largely unsuccessful, and COMINT and other collection systems were focused on North Korea and lacked the linguistic and technical capability to switch quickly. The USCIB had authorized increased COMINT coverage of mainland Chinese targets in March 1950, but it would take up to two years to develop effective processing of PRC military communications. (6) (8)
Further, the Chinese were successful in masking the true extent of their troop build-up in North Korea. Remarkably, they had moved more than 200,000 soldiers into attack positions against the UN command without being detected through a combination of expert field craft and camouflage, and their lack of any use of conventional means of detection, including radio transmissions, mechanized activity, and creation of supply dumps. Chinese troops moved only at night, avoided main roads, and made great efforts at remaining hidden during the day. (12)
MacArthur remained convinced that the PRC would not intervene. Even if they did he believed that US airpower would decimate the Chinese formations and the UN troops would prevail. (13) (12) Following his brilliant masterstroke at Inchon, MacArthur’s views were not easily challenged, but as more and more reports were received concerning Chinese soldiers in Korea, U.S. officials in Washington DC grew increasingly alarmed at MacArthur’s failure to take precautions. (15)

The UN Responds

In early 1951 UN forces had regrouped and had regained the initiative from the Chinese. In Feb 1951 UN forces launched a series of attacks which drove the Chinese and North Koreans back. On 14 Mar UN forces recaptured Seoul and on 27 Mar UN forces again crossed the 38th parallel. By the end of April 1951 UN forces were everywhere above the 38th parallel, except on the Ongjin Peninsula.
But this time there was no thought of advancing deep into North Korea. U.S. officials were content to restore the pre-war status quo and made known their desire for an armistice. UN officials agreed that a ceasefire roughly along the 38th parallel would meet the requirements of the UN Security Council Resolutions.
In April 1951 Chinese forces launched another major offensive, but after some initial gains they were halted by the rapidly improving UN forces. The failure of the April offensive convinced Chinese leaders that they lacked the military strength to reunify Korea. Both sides now sought a negotiated end to the conflict.
But General MacArthur opposed armistice talks and continued to advocate full-scale war against China, including nuclear strikes. Aggravated at MacArthur’s continued insubordination and fearful that his inflammatory remarks would jeopardize efforts to reach a negotiated settlement, President Truman removed MacArthur from command on April 11, 1951.

US Intelligence Operations in Korea 1950-1953

Before the North Korean invasion in June 1950, U.S. intelligence capabilities in the Far East were under-resourced and poorly coordinated. The inability to collect, process, and analyze useful intelligence on North Korean intentions and the failure to reconsider assumptions on the role of the Soviet Union were major factors in the failure of the United States to foresee the North Korean invasion. The outbreak of war created an immediate and overwhelming need for timely and accurate intelligence that U.S. officials struggled to meet. Although additional resources quickly became available, progress in creating or expanding intelligence organizations and operations was uneven. FECOM’s intelligence capabilities did expand rapidly, and by the time of the Inchon invasion in Sep 1950 FECOM’s intelligence picture had improved markedly. (6)
Despite these improvements, U.S. and UN intelligence on Chinese and North Korean strategic intentions remained poor throughout the war, primarily due to a virtually unsolvable lack of HUMINT capability and technical difficulties in collecting useful COMINT.
COMINT after 1950
Early in the war COMINT collection was also limited by a lack of trained linguists, supply shortages, outmoded gear, difficulties in determining good intercept sites, and fragile equipment. By 1951 large number of Korean linguists began arriving in theater, though there were never actually enough. Other problems were solved slowly as wartime needs caused a sharp rise in funding and other resources for intelligence. Within two months of the start of the Korean War, the Department of Defense authorized an increase of more than 1,900 military and civilian COMINT positions. Prior to the war DOD had twice denied the Joint Chiefs’ requests for additional COMINT personnel. But COMINT capabilities never achieved the success that they had in World War II. Throughout the war UN commanders remained dissatisfied with COMINT support. This dissatisfaction was a major factor in the eventual reorganization of US cryptology and the November 1952 creation of the National Security Agency. (8)
Throughout the war COMINT collection was hindered by a combination of factors, including the communist forces’ lack of sophisticated communications equipment, rigid security restrictions which limited the dissemination and use of COMINT, and the perennial lack of trained linguists. When useful COMINT was obtained it was usually the result of plain text intercepts and traffic analysis. Prior to the PRC entry into the war, AFSA experienced some success in exploiting PRC civil communications. (NSA/CSS)
During the first year of the war AFSA was successful in breaking North Korean cyphers, but in the summer of 1951 North Korea changed its codes and AFSA was unable to break them for the remainder of the war. (17) As the conflict continued, COMINT support became institutionalized and processes improved. COMINT units experimented with new technologies and had some success with ground-return intercept (GRI) and low-level intercept (LLI) equipment. Advance warning of communist attacks was occasionally achieved, but as the war settled into stalemate communist troops improved their communications security practices, reducing the quantity and quality of information that could be obtained through COMINT. (8)
HUMINT after 1950

In December 1951 the Combined Command for Reconnaissance Activities, Korea (CCRAK) was established to impose centralized control on the fragmented intelligence activities of the services, the CIA, and the ROK. CCRAK was controlled from Tokyo by Willoughby. To compensate for the lack of COMINT, CCRAK focused on developing HUMINT capabilities. CCRAK’s HUMINT efforts were managed by the Joint Advisory Commission, Korea (JACK), a combined CIA-military organization which was responsible for inserting and extracting U.S.-trained Korean agents into North Korea to gather intelligence, conduct sabotage, and rescue downed UN airmen.
A key objective in inserting agents into the north was to discover whether a local resistance movement might be created. But the intelligence obtained from these efforts was limited and the toll in lives was frightful. North Korean society was too closed, too militarized, and the North Korean regime’s repressive mechanisms too well-developed for UN agents to operate for long. No local resistance movement was possible. While a few agents provided useful information and made their way back to the South, most were quickly caught and either killed or turned into double agents. The overall casualty rate for the several hundred agents dispatched into North Korea was a shocking 80 percent. (12)
During the war FECOM made significant improvements to its clandestine HUMINT program, especially in the most problematic areas of agent insertion, communications, and training. In July 1951 FECOM established a semi-permanent clandestine HUMINT structure to be known as the Far East Command Liaison Detachment, Korea. The FECOM Liaison Detachment conducted a partisan war against North Korea by inserting bands of guerilla fighters raised from anti-communist refugees from North Korea. (6)
CIA after 1950
Following the outbreak of war in Korea a CIA station was established at Pusan and the Tokyo station was expanded to become the Office of Special Operations with responsibility for Far East intelligence collection. A new office, the Office of Policy Coordination, was established to conduct covert operations.
The outbreak of war generated strong demand for more comprehensive intelligence concerning Communist intentions in the Far East and around the world. The war years were a period of expansion and reorganization for the CIA, as the agency struggled to meet the government-wide demands for intelligence while defining its purpose and role.
During the war the CIA managed a clandestine program of raids, infiltration and other intelligence-gathering activities against mainland China from offshore islands – purpose: gather info, support indigenous guerilla resistance activities and conduct direct action attacks. (18)

Armistice Talks

Truce talks began at Kaesong on 10 Jul 1951, but the initial talks made no progress. Communist negotiators took a hard line and appeared to be seeking UN capitulation rather than a cease-fire. When after five weeks it became apparent that the UN would not accede to the Communist demands the Communists broke off the talks and fighting resumed. Over the next three months UN forces pushed the Communists back across the front and in October the Communists proposed to restart negotiations.
Talks resumed on 25 Oct 1951 at Panmunjom. The talks would go on for nearly two years during which UN forces suffered almost 60,000 casualties, including 22,000 American. Stalin reportedly directed that the talks be prolonged in order to keep US forces tied down and inflict as many casualties as possible.
From Feb 1952 until summer of 1953, the talks foundered on the issue of prisoner repatriation, with US negotiators insisting on voluntary repatriation and communist negotiators opposed. Dwight D. Eisenhower was inaugurated as president in Jan 1953 committed to achieving a cease-fire in Korea. Eisenhower began to openly the use of nuclear weapons in Korea if talks remained stalled. Whether he was sincere or not, his threats appeared to have alarmed the communists. The combination of strident rhetoric from Washington and the death of Stalin in March 1953 pushed the talks to a conclusion. On Jul 27, 1953, the armistice was signed – two years and seventeen days after the start of talks.

Conclusion

The armistice brought an end to the fighting, but not to the war, and not to the division of Korea. More than two million people lost their lives in the “limited war” fought in Korea from 1950-1953. The great majority of the dead were Korean civilians.
The war was started by Koreans to reverse a division of their country that they had neither participated in nor endorsed. But like the division of the country itself, the outcome of the war was decided by greater powers engaged in the pursuit of their own interests. The war itself was characterized by miscommunication, missed signals, misunderstandings, and self-delusions. The great powers most involved – the United States, the Soviet Union, and China – were repeatedly surprised by the actions of their adversaries and allies.
In the years between the end of World War II and the start of the Korean War U.S. intelligence capabilities had declined dramatically. Rapid demobilization of intelligence units, severe budget constraints, and the need to concentrate all available resources on the Soviet Union crippled the Far East Command’s intelligence apparatus and blinded U.S. officials to events occurring in North Korea and China. Yet while the majority of U.S. intelligence capabilities were directed at the Soviet Union, U.S. officials still misunderstood the exact nature of the relationship between the USSR and its allies and satellites, including China and North Korea. Throughout the Korean War – and indeed, throughout the entire Cold War – American officials consistently overestimated the influence of the Soviet Union on the actions of other communist states. In Korea, American officials failed to consider the possibility that North Korea and China might act to achieve their own foreign policy aims, without relying on or requiring explicit Soviet direction. As a result, when U.S. intelligence agencies reported on North Korean and Chinese troop movements and other preparations for war, U.S. policymakers discounted the warnings because they did not see evidence of Soviet readiness for war.
Lacking effective intelligence sources within China, U.S. officials failed to consider the impact of their statements and actions on the Chinese and failed to foresee the Chinese intervention. Despite explicit Chinese warnings against U.S. troops entering North Korea, U.S. officials refused to believe that the Chinese would intervene and even after Chinese troops engaged UN forces near the Yalu River, MacArthur remained unconvinced that the Chinese would attack in great strength.
On the communist side, neither Stalin not Mao nor Kim foresaw the American response to the North Korean invasion, in large part because the Americans themselves lacked a coherent strategy for Korea. U.S. efforts to deter a North Korean invasion through the use of ambiguous statements of intent failed spectacularly.
The war had far-ranging consequences which continue to shape the geopolitical landscape. The most significant result of the conflict was the decision of the United States to re-arm and implement the Cold War containment blueprint that had been laid out in National Security Council Report 68 (NSC-68) in April 1950. American defense spending quadrupled during the course of the war and it has never approached its pre-Korean War level. As a result of the war the United States undertook a vast re-armament program and created a worldwide system of military assistance pacts and overseas basing. The war poisoned relations between the United States and China for a generation as the United States committed itself to the defense of Taiwan. China was prevented from regaining Formosa but did gain recognition as a great power. But the war isolated China diplomatically and economically and increased its dependence on the Soviet Union, even while Chinese-Soviet relations deteriorated. The Soviet Union saw one of their biggest nightmares come true when President Truman dropped his opposition to the re-arming of West Germany. Britain’s unsolvable financial problems were worsened and the economy of Japan was kick-started, triggering the transformation of that nation. For the Koreans, South Korea was set on the path to become a modern industrial democracy while North Korea devolved into a paranoid garrison state with an oversized military and a brutally repressive government.
Like the rest of the U.S. national security establishment, U.S. intelligence organizations and capabilities were reinvigorated by the war in Korea. The CIA expanded dramatically and underwent a series of re-organizations that established it as the overall coordinator for all U.S. intelligence activities.

Notes:

1. Schnabel, James F.; United States Army in the Korean War, Policy and Direction: The First Year; Center of Military History, United States Army; Washington DC; 1992; pages 11-12, 46-65
2. Aldrich, Richard; Rawnsley, Gary D; and Rawnsley, Ming-Yeh T., editors; The Clandestine Cold War in Asia, 1945-65; Frank Cass, London; 2000; pages 17-63
3. Baum, Kim Chull and Matray, James I, editors; Korea and the Cold War; Regina Books, Claremont, CA; 1993; pages 95-109
4. Manchester, William; American Caesar; Little Brown and Company; Boston; 1978; pages 459-629
5. Goulden, Joseph C.; Korea: The Untold Story of the War; Times Books, New York, 1982; pages 37-41
6. Finnegan, John P.; “The Evolution of US Army HUMINT: Intelligence Operations in the Korean War”; Studies in Intelligence; Vol 55, No. 2 (Extracts, June 2011) Pages 57-69 (entire article)
7. Rose, P. K.; “Two Strategic Intelligence Mistakes in Korea, 1950”; CSI Publications, Central Intelligence Agency; Fall-Winter 2001; pages 1-15 (entire article)
8. Hatch, David; and Benson, Robert Louis; “The SIGINT Background”; National Security Agency / Central Security Service; undated paper; page 1-14 (entire paper)
9. Sloan, William; The Darkest Summer; Simon and Schuster; New York; 2009; pages 1-17
10. Bok, Lee Suk; The Impact of U. S. Forces in Korea; The National Defense University Press; Washington DC; 1987; (entire book)
11. Friedman, Norman; The Fifty Year War; The Naval Institute Press; Annapolis, MD; 2000; pages 149-170
12. Hastings, Max; The Korean War; Simon and Schuster; New York; 1987;
13. Stueck, William; Rethinking the Korean War; Princeton University Press; 2002; pages 61-117
14. Foot, Rosemary; The Wrong War; Cornell University Press; 1985; pages 55-131
15. Acheson, Dean; Present at the Creation; W. W. Norton & Co.; New York; 1969; pages 402-491, 512-539
16. Halberstam, David; The Coldest Winter; Hyperion; New York; 2007; pages 370-383
17. Johnson, Thomas R; American Cryptology During the Cold war, 1945-1989, Book I; National Security Agency, Center for Cryptological History; 1995
18. Holober, Frank; Raiders of the China Coast; Naval Institute Press; Annapolis, MD; 1999; pages 1-23

https://www.crcpress.com/Encyclopedia-of-US-Intelligence—Two-Volume-Set-Print-Version/Moore/p/book/9781420089578