On this day in July 1939, Polish codebreakers gave the secret of Enigma to their British and French counterparts. Marian Rejewski, acknowledged as the greatest cryptologist of all time, had cracked the code in 1932.
The Poles had enjoyed considerable success in decoding Enigma messages after Marian Rejewski’s achievement but their code breaking success had to kept secret-if the Nazi’s found out they would stop using the code and that route of outwitting the Nazi expansionist agenda would be lost.
In December 1938, the Nazi’s introduced an adaptation to the Enigma machine which made the codebreaking more difficult. The original machine had three interchangeable rotors –now there were five. The increased equipment and manpower required to crack the code were beyond the budget of The Cypher Bureau and they had to look to outside agencies for help.
They contacted their British and French Counterparts to arrange a meeting. The meeting took place at the cypher bureau headquarters in Kabacki Woods just outside Warsaw.
From the Cypher Bureau – Lieutenant Colonel Langer, Major Ciezki, Marian Rejewski, Henryk Zygalski, Jerzy Rozycki.
From Britain- Colonel Stewart Menzies, Alfred Dillwyn Knox, Alistair Denniston
From France-Captain Bertrand, Captain Branquenie.
The British and French reported that they had made no progress in breaking the Enigma code and considered it invincible.
The Poles had a terrible decision to make. Could they risk sharing information?- that would increase the risk of their success being discovered by the Germans. Or should they continue their work in secret-they knew risk of invasion was imminent.
They decided to share the information. The French and British codebreakers returned to their base with information on how to construct their own Enigma machines and full instructions on how to break the code together with the promise of a delivery of an Enigma machine.