Tap Code

The Tap Code is a cipher, commonly used by prisoners to communicate with one another. The method of communicating is usually by "tapping" either the metal bars or the walls inside the cell, hence its name. It is a very simple cipher, not meant to avoid interception, since the messages are sent in cleartext.

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.cite web | url=http://www.pbs.org/wgbh/amex/honor/sfeature/sf_tap.html | title="American Experience": "Return with Honor": The Tap Code | publisher=PBS | date=1999 | accessdate=2008-04-08]

The origins of this encoding go back to the Polybius square of Ancient Greece. As the "knock code", a Cyrillic alphabet version is said to have been used by nihilist prisoners of the Russian Czars. [David Kahn, "The Codebreakers - The Story of Secret Writing". 1967. ISBN 978-0-684-83130-5.] The knock code is featured in Arthur Koestler's classic 1941 work "Darkness at Noon". [Koestler, Arthur, "Darkness at Noon" (1941). Translated by Daphne Hardy. See page 19 of the Bantam Publishing paperback, 1981 printing for more info.] Smitty Harris had heard of the tap code being used by prisoners in World War IIcite news | url=http://www.au.af.mil/au/awc/awcgate/awc-pow.htm | title=Vets, Flyers discuss ideology, time in POW camps | author=Staff Sgt. Jason Tudor | publisher=Air Force News Service | date=1998-03-18 | accessdate=2008-04-08] and remembered a United States Air Force instructor who had discussed it as well.

In the Tap Code, each letter was communicated by tapping two numbers: the first designated the row (horizontal) and the second designated the column (vertical). The letter "X" was used to break up sentences and the letter "C" replaced the letter "K". Unlike Morse code, the tap code depended on actual taps, instead of the frequency and duration of each tap, to communicate a letter.

The Tap Code is outlined in the table below:

::

For example, to specify the letter "A", you would tap roughly the following: • •

Or to communicate the word "WATER" the cipher would be the following (the time between each pair of numbers is smaller than the one between two different letters):

..... .. . . .... .... . ..... .... .. (5,2) (1,1) (4,4) (1,5) (4,2) W A T E R

Because of the difficulty and length of time required for specifying a single letter, most prisoners devised abbreviations and acronyms for common items or phrases, such as "GN" for "Good Night", or "GBU" for "God Bless You".

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. [cite book | last=McCain | first=John | authorlink=John McCain | coauthors=Mark Salter | title="Faith of My Fathers" | publisher=Random House | year=1999 | isbn=0-375-50191-6 pp. 211–212.] It was even used when prisoners were sitting next to each other but not allowed to talk, by tapping on anothers' thigh.cite book | last=Brace |first=Ernest C. |authorlink=Ernest C. Brace | title=A Code to Keep: The true story of America's longest held civilian prisoner of war in Vietnam | publisher=St. Martin's Press | year=1988 | isbn=0709035608 pp. 171–172, 187–188.] By overcoming isolation with the tap code, prisoners were able to maintain a chain of command and keep up morale.

References

External links

* [http://www.braingle.com/brainteasers/codes/tapcode.php Online Tap Code Encoder/Decoder]