What was the "Ultra" secret of World War II?

I'm proud to say that my father worked at Bletchley Park.

Player Elf Counsel, the Enigma machine together with the broken code was given to the British by the Polish government. The British only continued and developed the work of the Polish mathematicians who broke the code long before WW2.

Dorania, it’s surprising how Poland is rarely mentioned when discussing Enigma

Alan Turing helped break the code with Enigma.