The First Residentura (PGU) - KGB (Soviet Union), the Committee for State Security, Komitet Gosudarstvennoy Bezopasnosti.
In the first years of existence Soviet Russia did not have many foreign missions that could provide official camouflage for legal outpost of intelligence called residentura, so, foreign department (INO) relied mainly on illegals, officers assigned to foreign countries under false identities. Later when official Soviet embassies, diplomatic offices and foreign missions have been created in major cities around the world, they were used to built legal intelligence post called residentura. It was led by resident his real identity was known only to the ambassador.
First operations of Soviet intelligence concentrated mainly on Russian military and political emigration organizations. According to Lenin directions foreign intelligence department has choose as his main target the White Guard people (White movement), which the largest groups were in Berlin, Paris and Warsaw. Intelligence and counter-intelligence department led long so called intelligence games, against Russian emigration, as a result of those games main representatives of Russian emigration like Boris Savinkov were
arrested and sent for many years to prisons. Another well known action against Russian emigration conducted in the 1920s was Operation Trust (Trust Operation). "Trest" was an operation to set up a fake anti-Bolshevik underground organization, "Monarchist Union of Central Russia", MUCR (Монархическое объединение Центральной России, МОЦР). The "head" of the MUCR was Alexander Yakushev (Александр Александрович Якушев), a former bureaucrat of Ministry of Communications of Imperial Russia, who after the Russian Revolution joined the Narkomat of External Trade (Наркомат внешней торговли), when the Soviets had to allow the former specialists (called "specs", "спецы") to take positions of their expertise. This position allowed him to travel abroad and contact Russian emigrants. MUCR kept the monarchist general Alexander Kutepov (Александр Кутепов), head of a major emigrant force, Russian All-Military Union (Русский общевоинский союз), from active actions, who was convinced to wait for the development of the internal anti-Bolshevik forces.
Among the successes of "Trest" was the luring of Boris Savinkov and Sidney Reilly into the Soviet Union to be arrested. In Soviet intelligence history 1930's have proceeded as a so called Era of the Great Illegals. Among others Arnold Deutsch and Yuri Modin, were officers leading Cambridge Five case.
One of the biggest successes of Soviet foreign intelligence was the penetration of the American Manhattan Project, it was the code name for the effort during World War II to develop the first nuclear weapons of the United States with assistance from the United Kingdom and Canada. Information gathered in United States, Great Britain and Canada, especially in USA, by NKVD and NKGB agents then supplied to Soviet physicists, allowed them to carry out first nuclear explosion already in 1949.