http://en.m.wikipedia.org/wiki/German_code_breaking_in_World_War_II

https://m.youtube.com/watch?v=9hAzmh6XSr8

http://www.history.co.uk/study-topics/history-of-ww2/code-breaking

http://www.bbc.co.uk/history/worldwars/wwtwo/enigma_01.shtml

Links information

http://en.m.wikipedia.org/wiki/German_code_breaking_in_World_War_II