The Enigma machine was once considered unbreakable, and the cracking of the "unbreakable code" by the allies changed the course of World War 2. This week, Plus talks to Nadia Baker from the Enigma Project about the history of codes and code-breaking, why the Enigma machine was considered unbreakable, the mathematics behind codes, and how it was finally cracked. The Enigma Project travels all over the United Kingdom and abroad, visiting over 100 schools and organisations, reaching over 12,000 people of all ages every year.