Got 'Authentication Required'<p>Google found me this. Least seedy looking source I could find.<p><a href="http://www.globalsecurity.org/intell/library/policy/army/fm/34-40-2/index.html" rel="nofollow">http://www.globalsecurity.org/intell/library/policy/army/fm/...</a>
<a href="http://www.und.nodak.edu/org/crypto/crypto/army.field.manual/" rel="nofollow">http://www.und.nodak.edu/org/crypto/crypto/army.field.manual...</a> contains zipped pdfs for each chapter.
I really like that this includes frequency tables for tetragraphs.<p>I had to laugh a little at the fact that "STOP" is the 5th most frequently used tetragraph though.