KGB (КГБ) is the commonly used acronym for the Russian: Комитет государственной безопасности​ (Komitet gosudarstvennoy bezopasnosti or Committee for State Security). It was the national security agency of the Soviet Union from 1954 until 1991, and was the premier internal security, intelligence, and secret police organization during that time. The KGB has been considered a military service and was governed by army laws and regulations, similar to the Soviet Army or MVD Internal Troops. While most of the KGB archives remain classified, two on-line documentary sources are available.

Since breaking away from Georgia de facto in the early 1990s with Russian help, South Ossetia established its own KGB (keeping this unreformed name). The State Security Committee of the Republic of Belarus also uses the acronym KGB.

The GRU (military intelligence) recruited the ideological agents Julian Wadleigh and Alger Hiss, who became State Department diplomats in 1936. The NKVD's first US operation was establishing the legal residency of Boris Bazarov and the illegal residency of Iskhak Akhmerov in 1934. Throughout, the Communist Party USA (CPUSA) and its General Secretary Earl Browder, helped NKVD recruit Americans, working in government, business, and industry.

Other important, high-level ideological agents were the diplomats Laurence Duggan and Michael Whitney Straight in the State Department, the statistician Harry Dexter White in the Treasury Department, the economist Lauchlin Currie (an FDR advisor), and the "Silvermaster Group", headed by statistician Greg Silvermaster, in the Farm Security Administration and the Board of Economic Warfare. Moreover, when Whittaker Chambers, formerly Alger Hiss's courier, approached the Roosevelt Government—to identify the Soviet spies Duggan, White, and others—he was ignored. Hence, during the Second World War (1939--45)—at the Teheran (1943), Yalta (1945), and Potsdam (1945) conferences—Big Three Ally Joseph Stalin of the USSR, was better informed about the war affairs of his US and UK allies than they were about his.

Soviet espionage succeeded most in collecting scientific and technologic intelligence about advances in jet propulsion, radar, and encryption, which impressed Moscow, but stealing atomic secrets was the capstone of NKVD espionage against Anglo--American science and technology. To wit, British Manhattan Project team physicist Klaus Fuchs (GRU 1941) was the main agent of the Rosenberg spy ring. In 1944, the New York City residency infiltrated the top secret Los Alamos National Laboratory in New Mexico, by recruiting Theodore Hall, a nineteen-year-old Harvard physicist.

The KGB failed to rebuild most of its US illegal resident networks. The aftermath of the Second Red Scare (1947--57), McCarthyism, and the destruction of the CPUSA hampered recruitment. The last major illegal resident, Rudolf Abel ("Willie" Vilyam Fisher), was betrayed by his assistant, Reino Häyhänen, in 1957.

Recruitment then emphasised mercenary agents, an approach especially successful in scientific and technical espionage—because private industry practiced lax internal security, unlike the US Government. In late 1967, the notable KGB success was the walk-in recruitment of US Navy Chief Warrant Officer John Anthony Walker who individually and via the Walker Spy Ring for eighteen years enabled Soviet Intelligence to decipher some one million US Navy messages, and track the US Navy.

In the late Cold War, the KGB was lucky with intelligence coups with the cases of the mercenary walk-in recruits FBI counterspy Robert Hanssen (1979--2001) and CIA Soviet Division officer Aldrich Ames (1985-1994).

//en.wikipedia.org/wiki/Kgb