He has a web page giving more insight. It includes a copy of National Security Action Memorandum (NSAM) 160 that had been sanitized. Unfortunately, the electronic version of the document is graphical, from a scanned FAX copy. For folks (and programs!) unable to read the memo in its graphical form, I've converted the documents to HTML. If you find any errors in my conversion, please let me know so I can make the corrections.
There are a few parts where the text is barely legible, in which case I made my best effort to convert the text faithfully.
Thanks to Steve Bellovin and Matt Blaze for shedding some light on an important piece of the history of cryptography.