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Polish intelligence

Jan Kowalewski, a polyglot and amateur cryptographer, broke the codes and ciphers of the army of the West Ukrainian People's Republic and of General Anton Denikin 's White Russian forces. In August 1919, he became chief of the Polish General Staff 's cryptography section in Warsaw. By early September, he had gathered a group of mathematicians from the University of Warsaw and the University of Lwów (most notably the founders of the Polish School of Mathematics – Stanisław Leśniewski, Stefan Mazurkiewicz and Wacław Sierpiński), who succeeded in breaking the Soviet Russian ciphers as well. During the Polish–Soviet War, the Polish decryption of Red Army radio messages made it possible to use Polish military forces efficiently against Soviet Russian forces and to win many individual battles, most importantly the Battle of Warsaw.