A U.S. Air Force C-123 sprays herbicides on dense jungle beside a South Vietnamese highway on May 18, 1966. This aircraft is the last in a formation of three. Spray from the other two planes can be seen ahead. U.S. Air Force via AP hide caption

itoggle caption U.S. Air Force via AP

After a photo of Lanny Martinson's dog tag was placed on Facebook and elsewhere, Marines and veterans helped track him down. Martinson lost the tag in Vietnam in 1968. Facebook hide caption

itoggle caption Facebook

Democratic presidential candidate George McGovern talks about the bombs being used in Vietnam at a $250-a-person fundraising dinner in Los Angeles on Sept. 27, 1972. AP hide caption

itoggle caption AP

July 1, 1971: After getting the green light from the Supreme Court, The New York Times resumes publication of its series of articles based on the secret Pentagon Papers. Jim Wells/AP hide caption

itoggle caption Jim Wells/AP