For Col. Carlyle “Smitty” Harris, the Tap Code provided him and fellow prisoners of war a way to communicate and resist the enemy. To hear the full story, stream The National Memorial Day Concert on our website, the PBS YouTube channel and PBS App. #memdaypbs PBS | National Memorial Day Concert (PBS)

This week, #DecipherCIA features Tap Code. In CIA's museum, there is a message encoded using tap code on the ceiling above an exhibition exploring "20 Years of War in Southeast Asia." During the Vietnam War, American prisoners of war used a tap code representing letters of the alphabet to communicate without detection. For 20 years, CIA worked to build up the newly independent Republic of Vietnam to resist its takeover by Communist forces. The fight would last from 1954 to 1974 and encompass Vie