Joan Clarke's ingenious work as a codebreaker during WW2 saved countless lives, and her talents were formidable enough to command the respect of some of the greatest minds of the 20th Century, despite the sexism of the time.
Clarke's mathematical abilities were first discovered by Gordon Welchman, in an undergraduate Geometry class at Cambridge. Welchman was one of the top four mathematicians to be recruited in 1939 to supervise decoding operations at Bletchley Park. After noticing Clarke's mathematical abilities he recruited her to join him at Bletchley Park and be a part of the 'Government Code and Cypher School' (GCCS).
The GCCS started up in 1939 with only one purpose, to break the German Enigma Code. The Enigma Code was a machine the Germans invented to encrypt their messages; they strongly believed their machine was unbreakable.