The existence of the GRU was not publicized during the Soviet era , although documents concerning it became available in the West in the late 1920s and it was mentioned in the 1931 memoirs of the first OGPU defector , Georges Agabekov , and described in detail in the 1939 autobiography ( I Was Stalin 's Agent ) of Walter Krivitsky , the most senior Red Army intelligence officer ever to defect .
Documents about it became available in the West in the late 1920s , and it was mentioned in the 1931 memoirs of the first OGPU defector , Georges Agabekov .