[2] During the Spanish Civil War (1936–39) he was appointed head of the Press Cabinet under Santiago Carrillo, Councillor of Public Security in the Madrid Defense Council.

[3] Other key posts in this department were held by Luis Rodríguez Cuesta (secretary of the Council), Federico Melchor (Security, Assault and the National Guard), Segundo Serrano Poncela (DGS), and Alfredo Cabello (Emisión Radiofónica).

[4] After the Republicans were defeated by the forces led by General Francisco Franco in 1939, Claudín began a long exile in Moscow, France, Mexico, Cuba, Chile and Argentina.

In June 1975 he returned secretly to Spain and worked at the Editorial Siglo XXI until 1980, when he was named a director of the Fundación Pablo Iglesias.

[2] Among other works, Claudín wrote a critical Marxist history of the Soviet-aligned Communist movement La crisis del movimiento comunista.