The article is dedicated to the activities of the Soviet intelligence agencies in Spain during the Civil War of 1936-1939. By June 1936, diplomatic relations between USSR and Spain were absent. Due to the putschist revolt and the appeal of the legitimate government of Spain to the USSR, the Politburo of the Central Committee of the Communist Party (Bolshevik) made a decision to establish diplomatic, military, and trade delegations in Spain. The intelligence agencies of the USSR planned operation ‘X’ for military assistance to Spain. As part of this operation, a Soviet advisory staff concerning military and foreign intelligence was formed. The author brings to light the goals of the secret service authorities of the Soviet Union, including such particular ones as the removal of Spain’s gold reserve and the creation of the 14th Partisan Corps. The article analyses the activities of the advisory staff, their role in the development of the largest military operations during the Spanish Civil War, and traces the f