Wartime Crypto Laws

Gentlemen, It was recently mentioned on this list that there were additional restrictions placed on the use of ciphers by private citizens during World War II. I'm curious if anyone knows of a good resource for further information on this topic. (Now, inevitably, Choate is going to sent me a Google URL. This is fine, since I wasn't able to get Google to give me anything but information on documents discussing recent export restrictions, happening to mention WWII.) Thank you. -MW-