The National Cryptologic School - On Watch, Profiles from the National Security Agency's Past 40 Years, is a 76 page document that highlights some of the key moments in the history of the National Security Agency (NSA).
The document starts with Japan's last days of war and the transition from the different American wartime cryptology efforts into one post-war agency in Arlington Hall that controlled the Army Security Agency, the Naval Security Group, and the Air Force Security Service. However, the in 1949 created Armed Forces Security Agency (AFSA) lacked the power to enforce a real centralized coordination between the individual parts of the intelligence community.
Meanwhile, the 1945 defection of GRU officer Igor Gouzenko in the Soviet Embassy of Ottawa was used by U.S. intelligence as a cover to release communications intelligence. The Soviets however knew, through a source inside Arlington Hall, that their communications were not compromised by Gouzenko but by the vulnerability of their systems. It was the start of a Soviet research program to improve their Communications Security, which resulted in the 1948 blackout of American and British intelligence on the Soviet communications.
The sudden change in radio procedures and the use of one-time pads for all Soviet high level traffic was a disaster that took six years to overcome. In 1949, AFSA codebreakers discovered the double use of one-time pads in old Soviet intelligence traffic, giving them various clues on Soviet infiltration of U.S. intelligence services. This initiated several counter-intelligence operations. The results of this operation, now called VENONA, eventually unveiled the Cambridge spy ring (Phylby, Maclean, Blunt and Burgess), atom bomb spy Klaus Fuchs and many other agents (see also VENONA Declassified).
AFSA's successor, the National Security Agency, was created in 1952. The United States finally had its centralised cryptologic intelligence agency. The Korean War was NSA's trial of fire, which resulted in a dearly needed reorganisation of its communications capabilities. The explosion of the French-Vietnamese conflict and fear for Soviet expansion initiated a major SIGINT buildup in Southeast Asia in the early 1960's. It was soon followed by thousands of U.S. military advisors. In the 1964 Gulf of Tonking incident, USS Maddox, a destroyer on DESOTO patrol (SIGINT missions in hostile waters), was attacked by North Vietnamese torpedo boats. It would be the prelude to a complete involvement of American armed forces and intelligence in Vietnam.
NSA's SIGINT efforts would continue to play a major role in combat operation, with signals collection both on the ground and in the air, until the end of the Vietnam war in 1975. Vietnam also fueled the development of miniaturized voice encryption equipment. The secure voice system NESTOR became a widely used standard during that war. During this conflict, NSA also suffered many losses, as you can read in my Silent Warriors post.
The agency quickly outgrew its former girl's school in Arlington. In 1966, NSA relocated to its current buildings in Fort Meade to keep up with the ever growing work load. Nothing, however, could prevent the intelligence disaster that struck NSA two years later, when USS Pueblo AGER-2, a SIGINT vessel, operating near North Korean waters, was attacked and seized by the North Koreans. Loaded with SIGINT equipment and a vast amount of highly classified documents, the ship was a treasure trove for the North Koreans and their Soviet allies. The compromise of equipment, documents and knowledge effected NSA's SIGINT capabilities for many years (see also USS Pueblo Incident).