Sources

  http://www.bbc.co.uk/history/topics/enigma

  http://www.cryptomuseum.com/crypto/enigma/patents/

  http://ww2db.com/battle_spec.php?battle_id=92

  http://www.bletchleypark.org.uk/content/hist/worldwartwo/enigma.rhtm

  http://www.independent.co.uk/arts-entertainment/films/news/the-imitation-game-film-new-trailer-shows-benedict-cumberbatch-as-alan-turing-struggling-to-crack-the-enigma-code-9769161.html