US Army Field Manual: Basic Cryptanalysis (1990)

Got 'Authentication Required'

Google found me this. Least seedy looking source I could find.

http://www.globalsecurity.org/intell/library/policy/army/fm/...

Worked for me just now (7 minutes after your post).

Minor general complaint to people tarring up stuff for download; It's always useful to provide a useful title and/or author to identify the file, instead of something like 'pdf.tar.gz' or something equally distinguished.

EDIT: I'm not wanting to sound ungrateful, it can just be a little difficult to notice or remember to fix a name, and then... hunt the file time ;)

Weird, still works for me (or works again).

But yes, same material as your source.

3yo https://archive.is/oM5Q (only the index page is archived, the links will redirect to the originals, if you had trouble getting the index, they might be blocked too)

http://www.und.nodak.edu/org/crypto/crypto/army.field.manual... contains zipped pdfs for each chapter.

I really like that this includes frequency tables for tetragraphs.

I had to laugh a little at the fact that "STOP" is the 5th most frequently used tetragraph though.