CCCP vs Union of Soviet Socialist Republics

CCCP

name

  • USSR (Union of Soviet Socialist Republics) 

  • Central Committee of the Communist Party 

Union of Soviet Socialist Republics

name

  • A nation in Eurasia that existed from December 30, 1922 to December 26, 1991. 

How often have the words CCCP and Union of Soviet Socialist Republics occurred in a corpus of books? (source: Google Ngram Viewer )