CIA activities in North Korea
Democratic Peoples' Republic of Korea (North Korea) (DPRK).
"In the 16 July 1949 Weekly Summary, the Agency describes North Korea as a Soviet puppet regime. On 29 October, a Weekly Summary states that 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 decisionmaking. 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. Any scholarly counterbalances to this view, either questioning the absolute authority of Moscow over other Communist states or noting that cultural, historic, or nationalistic factors might come into play, fell victim to the political atmosphere.
In April 1950, the Army Security Agency, a SIGINT agency operating before the creation of NSA, undertook a limited "search and development" study of DPRK traffic. CIA received its reports. Two positions the second case, as revealed in COMINT, large shipments of bandages and medicines went 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. 
By the spring of 1950, North Korea’s preparations for war had become...recognizable. 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. 
Intelligence analysis (CIA)
On 6 June, CIA reported another interesting international development: all East Asian senior Soviet diplomats were recalled to Moscow for consultations. The CIA believed the purpose of the recall was to develop a new plan to counter anti-Communist efforts in the region.
On 20 June 1950, the CIA published a report, based primarily on human assets, concluding that the DPRK had the capability to invade the South at any time. President Truman, Secretary of State Acheson, and Secretary of Defense Johnson all received copies of this report. 
On 25 June, the Army of the Democratic People’s Republic of Korea (DPRK) invaded across the 38th parallel. This was a surprise to US intelligence.
A report obtained from a "secret" Russian foreign ministry meeting states that North Korea's Nodong-1 is "not useful as a military weapon," based on its poor performance in all areas during a test-firing in the Sea of Japan/East Sea in 1993. The report quoted Yu Min in the Seoul Sinmun, 5 January 1996, p.2.
On 2 February, Director of Central Intelligence John Deutch tells a US Senate Select Committee that North Korea is developing long-range missiles. The United States, according to Deutch, should focus on stopping North Korea from acquiring guidance-and-control technology that could make its long-range missiles more accurate and lethal.
In a 9 May article in Aerospace Daily, pp. 233-234, a National Security Council director, Robert G. Bell, says that a US National Intelligence Estimate which concluded that no new strategic missile system will threaten the continental United States reflects a consensus within the US intelligence community. Bell admits, however, that the intelligence community's knowledge of North Korea's Taepodong-2 program is incomplete.
Bill Gertz, of the Washington Times, wrote on 21 June (pp. A1, A22) that CIA sources said North Korea delivered seven shiploads of Scud-C missiles to Egypt between March and April 1996. The missile shipments were part of a 1980s licensing agreement between Egypt and North Korea.
On December 11, according to Barbara Starr of Jane's Defence Weekly (p. 10) Former CIA Director Robert Gates told the US Senate Intelligence Committee that North Korea is having problems developing its Taepodong class of ballistic missiles. He said that research and development were needed for a completely new propulsion system, plus improved guidance. Gates said that economic, technical, and manufacturing problems in North Korea's infrastructure make the development of this new class of missiles unlikely. The US intelligence community was confident that the first flight tests of the missile will provide at least five years warning before deployment. 
- Rose, P.K., "Two Strategic Intelligence Mistakes in Korea, 1950: Perceptions and Reality", Studies in Intelligence, retrieved 2007-12-19
- Hatch, David A.; Robert Louis Benson, The Korean War: The SIGINT Background ([dead link] – Scholar search), National Security Agency, archived from the original on 2007-09-03, retrieved 2007-10-07
- James Martin Center for Nonproliferation Studies, North Korea's Ballistic Missile Program, CNS Resources on North Korea's Ballistic Missile Program, Chronology of North Korea's Missile Trade and Developments: 1996-1998 ([dead link])