When Rejewski had been working on reconstructing the German military Enigma machine in late 1932, he had ultimately solved a crucial element, the wiring of the letters of the alphabet into the entry drum, with the inspired guess that they might be wired in simple alphabetical order.
A week after the Pyry meeting, Dillwyn Knox, in a letter dated 1 August 1939, thanked the Poles, in Polish, "for your cooperation and patience."