the north face fleece Intelligence on the Korean War
When the army of the Democratic People’s Republic of Korea (DPRK, “North Korean” army. also NKPA) attacked the Republic of Korea (ROK, “South Korea”) on June 15, 1950, it was a surprise to the United States and the Republic of Korea. intelligence structure. It is less clear why South Korea also was surprised at the highest levels. Still, the warnings were from relatively low ranking levels and not definitive. tactical units had left South Korea in 1949, leaving only the Korea Military Assistance Advisory Group (KMAG), which did not report to Douglas MacArthur, commanding Far Eastern Armed Forces. MacArthur had his own intelligence organization, “G 2”, under MG Charles Willoughby, but FEAF G 2 did not have an explicit intelligence responsibility for Korea. responsibility in the field. had concluded that withdrawing its occupation troops would probably lead to an invasion, but the Joint Chiefs of Staff did not want to fight in Korea, believing that the conditions would be too favorable to the other side. Essentially, Korea had been written off.
In mid 1949, however, Chief of Staff of the Army Omar Bradley had his staff develop a plan to bring the matter before the United Nations should there be an invasion, and, if diplomacy failed, form a UN multinational military force.
Failure to anticipate
Failure to anticipate the attack on the South was, in part, a result of the combined cutbacks in military and intelligence budgets after World War II, and the containment strategy against the Soviet bloc, which was principally focused on the Soviet Union itself, on China to a lesser extent, and essentially ignoring small bloc states such as North Korea. had written off Korea as strategically significant. Korea Military Assistance Group (KMAG), who worked with ROK counterparts to analyze intelligence on North Korea. KMAG reported to Washington, not MacArthur.  It had the intelligence responsibility, sent reports to Washington, which sent it, along with CIA and other reports, to MacArthur. They sent this information to Washington periodically and on occasion made special reports. Other agencies and units in the Far East reported to appropriate officials in Washington. Communications intelligence monitored North Korean communications only to the extent that they provided information on Soviet activities.
An additional problem was that Douglas MacArthur wanted intelligence under his direct control. During the Second World War, he had not allowed the predecessor of the Central Intelligence Agency, the Office of Strategic Services, to operate in his theater. intelligence, especially clandestine human source intelligence, was in a bureaucratic limbo between 1945 and 1952, when the CIA obtained firm control of clandestine human source intelligence and covert action.
Instead, he kept his own intelligence organization under his trusted intelligence officer, MG Charles Willoughby. In early 1950, General J. Lawton Collins asked MacArthur if he could provide information on areas outside his responsibility. MacArthur was reluctant to commit to regular reporting without orders to do so, but he thought he had the personnel to do so. 
“By late 1949, the KLO was reporting that the Communist guerrillas represented a serious threat to the Republic of Korea (ROK).” Willoughby also claimed that the KLO had 16 agents operating in the North. KLO officers in Seoul, however, expressed suspicion regarding the loyalty and reporting of these agents. Separate from Willoughby’s command, then Capt. John Singlaub had established an Army intelligence outpost in Manchuria, just across the border from Korea. Over the course of several years, he trained and dispatched dozens of former Korean POWs, who had been in Japanese Army units, into the North. Their instructions were to join the Communist Korean military and government, and to obtain information on the Communists’ plans and intentions.
Still, CIA did have an analytic function under its control, and issued reports. While its 16 July 1949 Weekly Summary dismissed North Korea as a Soviet “puppet”, the 29 October Summary suggested a North Korean attack on the South is possible as early as 1949, and cites reports of road improvements towards the border and troop movements there. 
“These reports establish the dominant theme in intelligence analysis from Washington that accounts for the failure to predict the North Korean attack that the Soviets controlled North Korean decision making. The Washington focus on the Soviet Union as “the” Communist state had become the accepted perception within US Government’s political and military leadership circles. Army communications intelligence made a limited “search and development” study of DPRK traffic. CIA received its reports. The COMINT revealed large shipments of bandages and medicines from the USSR to North Korea and Manchuria, starting in February 1950. These two actions made sense only in hindsight, after the invasion of South Korea occurred in June 1950. Monthly CIA reports describe the military buildup of DPRK forces, but also discount the possibility of an actual invasion. It was believed that DPRK forces could not mount a successful attack without Soviet assistance, and such assistance would indicate a worldwide Communist offensive. There were no indications in Europe that such an offensive was in preparation. 
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. 
A surprise attack
In hindsight, there were warnings, in May June 1950, of a potential attack in the near future. These reports noted the removal of civilians from the border area, the restriction of all transport capabilities for military use only, and the movements of infantry and armor units to the border area. Also, following classic Communist political tactics, the DPRK began an international propaganda campaign against the ROK police state. policymakers that all East Asian senior Soviet diplomats were recalled to Moscow for consultations. Unfortunately, it was assumed this was to consult about a new plan to counter anti Communist efforts in the region. On 20 June 1950, the CIA published a report, based primarily on HUMINT, concluding that the DPRK had the capability to invade the South at any time. President Harry S. Truman, United States Secretary of State Dean Acheson, and United States Secretary of Defense Louis Johnson all received copies of this report. 
On June 25, 1950, Kim Il Sung, the leader of Communist North Korea, sent troops of the North Korean People’s Army (NKPA) across the 38th parallel and invaded South Korea, heading toward its capital, Seoul.
MacArthur’s headquarters “learned of the attack six and one half hours after the first North Korean troops crossed into South Korea. The telegram bearing the news from the Office of the Military Attach in Seoul reported:
Fighting with great intensity started at 0400, 25 June on the Ongjin
Peninsula, moving eastwardly taking six major points; city of Kaesong
fell to North Koreans at 0900, ten tanks slightly north of Chunchon,
landing twenty boats approximately one regiment strength on east
coast reported cutting coastal road south of Kangnung; Comment: No
evidence of panic among South Korean troops.
A message ninety minutes later gave confirmation. General MacArthur immediately informed Washington and, within a few hours, sent the first comprehensive situation report on the Korean fighting.”CIA intelligence reports, after the invasion, still treated North Korea as controlled by the USSR, but the reports did raise the possibility of Chinese involvement. On 26 June, CIA agreed with the US Embassy in Moscow that the North Korean offensive was a “. clear cut Soviet challenge to the United States”