Tap Code - History

History

The origins of this encoding go back to the Polybius square of Ancient Greece. As the "knock code", a Cyrillic script version is said to have been used by nihilist prisoners of the Russian Czars. The knock code is featured in Arthur Koestler's classic 1941 work Darkness at Noon.

United States prisoners of war during the Vietnam War are most known for having used the tap code. It was introduced in June 1965 by four POWs held in the Hoa Lo "Hanoi Hilton" prison: Captain Carlyle "Smitty" Harris, Lieutenant Phillip Butler, Lieutenant Robert Peel, and Lieutenant Commander Robert Shumaker. Smitty Harris had heard of the tap code being used by prisoners in World War II and remembered a United States Air Force instructor who had discussed it as well.

In Vietnam, the tap code became a very successful way for otherwise isolated prisoners to communicate. POWs would use the tap code in order to communicate to each other between cells in a way which the guards would be unable to pick up on. They used it to communicate everything from what questions interrogators were asking (in order for everyone to stay consistent with a deceptive or bogus story), to who was hurt and needed others to donate meager food rations. It was easy to teach and newly arrived prisoners became fluent in it within a few days. It was even used when prisoners were sitting next to each other but not allowed to talk, by tapping on anothers' thigh. By overcoming isolation with the tap code, prisoners were able to maintain a chain of command and keep up morale.