The Third Communist International—so called because it followed the “first,” Karl Marx’s International Working Men’s Association, founded in London in 1864, which had lasted only nine years, and the “second,” created in Paris in 1889, the Labour International, which had been condemned by Vladimir Lenin as having sold out to the social democrats—came into being in March 1919 to promote the Bolshevik objective of world revolution. Initially headed by Grigori Zinoviev until he was replaced in 1926 by Nikolai Bukharin, the Comintern was run from July 1935 by a Bulgarian Communist, Georgi Dmitrov. Its dissolution was announced in 1943.
Although intended to support, coordinate, and direct individual national Communist movements, the Comintern actively engaged in espionage and its International Directorate communicated in code to trusted members of the organization across the globe. These agents, usually vetted by the leadership in their own countries, often had attended the Lenin School in Moscow for up to two years, taking overt classes in political ideology while also attending parallel courses in tradecraft and clandestine communications. Created in October 1926, with up to a thousand students in residence, the International Lenin University acted as an espionage finishing academy for candidates drawn from mainly English-speaking countries (chiefly Great Britain, Ireland, India, Canada, and the United States), mixed with smaller groups from Spain, France, Germany, and China. All returned to their countries of origin as indoctrinated organizers and propagandists, if not fully-fledged professional spies.
The Comintern’s Otdel Mezhdunarodnykh Svyazey (OMS, Foreign Liaison Department) acted as an adjunct to the two main Soviet intelligence services, but there was often an overlap in their separate networks. In Great Britain this became apparent when the enciphered communications exchanged between Moscow and OMS spy rings in Great Britain were read by the Government Code and Cypher School.
Because the OMS had full confidence in its cipher system and never learned that its integrity had been compromised, the messages were quite informal, if not indiscreet, with only some of the corresponents taking the trouble to adopt cover names to conceal their true identities. Even when they did so, their security procedures were appallingly lax by modern standards, thereby allowing the cryptanalysts to exercise their arcane skills and between 1934 and 1937 to circulate the traffic to selected recipients under the code name MASK.