The Enigma Machine
In 1915, two Dutch Naval officers invented a machine to encrypt messages. This became known as the Enigma machine. In 1918, Arthur Scherbius, a German businessman, patented the Enigma machine. In the mid 1920s, the mass production of Enigma machines with 30,000 machines being sold to the German military over the next 2 decades. The Poles set up a world leading crypt analysis bureau and hired leading mathematicians such as Marian Rejewski. He Built his own model of the Enigma Machine without seeing it.
In 1931, a German traitor told Rejewski that the Germans routinely changed the daily key indicator setting for the codes. To find the daily key, Rejewski build 6 replicas of the Enigma machine and connected them.