In the aftermath of World War II, one of the thorniest problems for the United States was the status of Korea.

The peninsula had been an independent nation for centuries before the Japanese took it as a colony in 1910, but it was unclear whether Koreans could govern themselves after three decades of foreign rule. In August 1945, Soviet forces were fighting the Japanese military on the China-Korea border, and there was concern that the Red Anny might occupy the Korean peninsula.

The U.S. solution was to propose a temporary division of the country. Americans would take the Japanese surrender in the southern sector, Soviet troops in the north. After a suitable — but undefined — period in which Koreans would be prepared for self-rule, both armies would withdraw. The Soviets agreed to this plan, and Korea was divided on either side of the 3 8th parallel.

However, as the Cold War developed, the peninsula became a pawn in a larger, international ideological struggle, and neither of the superpowers withdrew its troops from Korea. After three years, the United States turned the problem over to the United Nations, which mandated elections to decide on a unified government in Korea. UN-sponsored elections led to the formation of the Republic of Korea (ROK) on August 15, 1948, with its capital in Seoul. North Korea declined to participate in the UN elections and formed its own government, the Democratic People’s Republic of Korea (DPRK), with its capital in Pyongyang.

The next two years were marked by struggle on many levels, military, political, and ideological. Small unit clashes and armed incursions along the 38th parallel were frequent. Both the ROK and the DPRK built up military forces, but there was a difference: the USSR supplied armor and aircraft to Pyongyang, while the U.S. denied them to Seoul.

More ominously, U.S. officials declared South Korea outside the American defense perimeter in the Pacific region.

In the five years before the Korean War, U.S. communications intelligence underwent major structural and doctrinal changes. The Army Security Agency (ASA) shared the national COMINT mission with the Navy’s Communications Supplementary Activity (COMMSUPACT)– which became the Naval Security Group in June 1950. When the independent Air Force was created in 1947, Army cryptologic assets were resubordinated to the new organization as the Air Force Security Service (AFSS).

Many officials favored centralization of cryptologic activities, and in 1949 the Department of Defense created the Armed Forces Security Agency (AFSA) as a national organization. The existence of AFSA forced the Service Cryptologic Agencies to redefine their roles, and they began structuring themselves to provide direct COMINT support for American fighting forces.

As it turned out, however, AFSA did not have sufficient legal authority or adequate financial resources to provide central direction to cryptologic work. Proposals for increases to AFSA’s budget or personnel allocations were not approved.

It was in these circumstances that the Korean War began.

Early on Sunday morning, 25 June 1950, the North Korean People’s Army (NKPA) crossed the thinly defended border with South Korea and began pressing on. The NKP A, equipped with Soviet armor and aircraft, quickly smashed through the smaller, less-well equipped and less-well-trained army of the ROK; within several days, communist forces were poised to capture Seoul.

Even though the U.S. government had previously suggested that South Korea lay outside its security perimeter, American response was quick. Even before receiving presidential authorization, General Douglas MacArthur in Tokyo dispatched air forces to support the withdrawal of U.S. citizens and began contemplating the use of American ground troops.

The question was asked during the war and in the intervening half century: was there intelligence warning, specifically COMINT warning, about the outbreak of the Korean War?

The short answer is no.

The CIA, based on HUMINT reporting, stated early in 1950 that the North Koreans were capable of an invasion, but there was no reliable data on DPRK intentions. Prior to June 1950, there had been no sustained communications intelligence collection against North Korea: the priorities had been too low, and the resource-poor COMINT agencies had had no collection positions to spare.

The COMINT agencies maintained two requirements lists. The first consisted of subjects of “greatest concern to U.S. policy or security,” such as “Soviet intentions to launch an armed attack.” The second list was items of “high importance”; for the month prior to the war, Japan and Korea were item no. 15 on the B List, but the specific requirements were “Soviet activities in North Korea,” “North Korean – Chinese Communist Relations,” and “North Korean – South Korean relations, including activities of armed units in border areas.”

Intercept facilities in the Pacific region were relatively few. All were directed toward higher priority targets, primarily Chinese Communist activities, but also the Philippine Huk rebellion. Other intercept targets could be covered only by diverting collection from existing ones.

Some North Korean communications were intercepted between May 1949 and April 1950 because the operators were using Soviet communications procedures. Coverage was dropped once analysts confirmed the non-Soviet origin of the material. Also, in April 1950 ASA undertook a limited “search and development” study of DPRK traffic. Two positions were assigned intercept of internal North Korean communications, and some 220 messages were on hand at the time the war began, although none had been processed.

Immediately after the invasion of South Korea, all available U.S. intercept positions in Japan were redirected to Korean collection. Even the 50th Signal Service Detachment, whose mission was to monitor U.S. forces to ensure communications security, was diverted to wartime support. Direction finding and traffic analysis became important as initial sources of information.

As more traffic became available, the Service Cryptologic Agencies and AFSA solved virtually all cryptosystems in use by the North Korean Army and began providing high-quality COMINT to American forces. One of the earliest, if not the earliest, messages relating to the war, dated June 27 but not translated until October, stated that the North Korean Third Division had occupied P’och’on, a town below the 38th parallel, on June 25.

ASA and AFSA moved to dispatch units for support of combat operations. A small advance ASA unit arrived in Korea in mid-September 1950 and was assigned to combat support. The 60th Signal Service Company, based in Fort Lewis, Washington, considered the best prepared of the existing tactical ASA units in the Far Eastern Command, was dispatched to the war zone. It did not arrive, however, until early October, three months after hostilities had commenced. It still found plenty to do.

The outbreak of the Korean War led to increased funding and more billets across the board for the military and the national intelligence agencies, including the cryptologic community. Wartime pressures exposed weaknesses in the organization for cryptologic efforts, and led to changes both in direct support for combat forces and in central organizations.

Source: NSA
FOIA Case #51629