Intelligence personnel often accompanied units conducting offensive operations into communist territory. When the 11th Armored Cavalry Regiment found and raided a Viet Cong bunker complex about 3 miles from the South Vietnamese border—in hitherto off-limits Cambodia—on May 3, 1970, the troops recovered a trove of documents, turned over to the “intel guys” for meticulous examination. One never knew what one would find, and Americans welcomed anything that might provide clues for outwitting an already-elusive and resourceful enemy. (Bettman/Getty Images)