ALT On the left is a photo of the cover of "Unarmed and Unafraid," while on the right is a photo of a U-2 spy plane flying against the sky. (Photo Credits: Abe Books and the Defense Visual Information Distribution Service photograph by Airman 1st Class Tristan Viglianco, 9th Reconnaissance Wing Public Affairs; modified by the Army Geospatial Center)

ALT The title of the book "Air Spy: The Story Of Photo Intelligence In World War II." (Source Credit: Internet Archive, modified by the Army Geospatial Center)

ALT The book cover of "The Defence of Duffer's Drift" showing a cartoon of a British Soldier in the Boer War. In the background is a physiographic diagram of a u-shaped valley with steep walls. (Credits: Book cover is from Wikipedia. The physiographic diagram was taken from the Army University Press publication of the book. The combined image was prepared by the Army Geospatial Center.)