Between 1964 and 1973, during the Vietnamese War, many American servicemen, primarily officers (pilots) were held in North Vietnamese prisons. The most famous was the Hoả Lò Prison, sarcastically known as the “Hanoi Hilton”. Communication between prisoners was often forbidden, until Captain Smitty Harris, Lts. Phillip Butler and Robert Peel and LCdr Robert Shumaker found a way around the prohibition in June 1965.
In 1973, 591 American prisoners were repatriated, although 1,350 prisoners of war and MIAs (missing in action) were still listed as missing, along with 1200 US KIAs (killed in action), whose bodies were not recovered.
While planning to visit my daughter in Louisiana, I looked over several caches in her area and found a fantastic one by Jägermeister, whose idea I have shamelessly stolen for this one. Cache may not be easily found on the ground in winter, but it's still a cool puzzle