Marian Rejewski (1905–1980), Jerzy Różycki (1909–1942) and Henryk Zygalski (1908–1978) were mathematicians in the Polish Cypher Bureau (Biuro Szyfrów). They famously achieved an astonishing feat of intellectual reverse-engineering that is believed to have saved the Allies years of trial and error.
In 1932, using little more than group theory and clues from a French spy, they mapped the internal wiring of the German military Enigma machine. Their work was handed to British and French intelligence just weeks before the invasion of Poland and provided the essential head start for Alan Turing and the team at Bletchley Park.