uh wwii enigma was cracked at bletchly park based on the work of some poles who had been trying to figure out when they would be invaded entirely mechanical definitely not optical at all enigma was originally broken based on bad use practice if it had been employed more sensibly it would have been a lot harder see the code book by singh doubleday NUMBER or for that matter cryptonomicon by stephenson which is a fictionalization of the enigma cracking story and pretty accurate i eventually get born as a side effect of the battle of britain you see computing with interference patterns etc makes perfect sense but enigma was cracked by building mechanical systems that were essentially enigma machines and brute forcing eirikur 