An unclassified U.S. Army history of military intelligence that was formerly used as a textbook in officer training at the Army Intelligence Center at Fort Huachuca is now publicly available online (large pdf).
The 1973 volume has been superseded in many or even most respects by subsequent research and publication. But it retains some interest as a snapshot of the contemporary self-understanding and presentation of military intelligence. “It remains one of the best overviews of the history of Army Intelligence, although it is dated,” one admirer of the document told Secrecy News.
According to the Preface, “This history concentrates on intelligence support to tactical forces since, in truth, this is where military intelligence, per se, receives its greatest visibility and its greatest importance.”
See “The Evolution of American Military Intelligence” by Marc B. Powe and Edward Wilson, U.S. Army Intelligence Center and School, Fort Huachuca, AZ, May 1973.