Polish cryptographers had provided a head start by decoding three-rotor Enigma messages before the outbreak of the war. Three young Polish mathematicians (Henryk Zygalski, Jerzy Rózycki, and Marian Rejewski), assisted by French intelligence and with an interest in the German Enigma dating back to an interception by Polish customs officers in 1928, narrowed the search for rotor configurations so that electromechanical devices (called “bombas” by the Poles and “bombes” by the British) could apply trial and error to certain subsets that remained.
