Polish Enigma double

In December 1932 the Cipher Bureau tasked Marian Rejewski with reconstructing the Enigma machine.

In February 1933, the Polish Cipher Bureau ordered fifteen "doubles" of the military Enigma machine from the AVA Radio Manufacturing Company, in Warsaw.

In August 1939, following a tripartite meeting of Polish, French, and British cryptologists at Warsaw on 25–26 July 1939 – during which the Poles had explained all their Enigma-decryption methods and equipment – two Enigma replicas were passed to Poland's allies, one sent to Paris and one to London.

After Germany invaded Poland in September 1939 and key Polish Polish Cipher Bureau personnel had been evacuated to France, the Cipher Bureau resumed its interrupted work at PC Bruno outside Paris.

The Poles had only three replica Enigmas to work with,[9] two secretly taken out of Poland during the evacuation, and the one that had been sent to France after the July 1939 Warsaw conference, and these were wearing out from round-the-clock use.

Prewar Polish Enigma double
One of four Enigma doubles assembled in France in 1940, featuring ABCD keyboard layout. In Józef Piłsudski Institute, London .