Tap Code

History

In June 1965, four POWs -- Captain Carlyle ("Smitty") Harris, Lieutenant Phillip Butler, Lieutenant Robert Peel and Lieutenant Commander Robert Shumaker -- who were imprisoned in the same cell in Hoa Lo devised a simple, secretive code.

Harris remembered an Air Force instructor who had shown him a secret code based on a five-by-five alphabet matrix. Each letter was communicated by tapping two numbers: the first designated the horizontal row and the second designated the vertical row. The letter W, for example, would be 5-2; the letter H would be 2-3. The letter x was used to break up sentences and the letter "c" replaced the letter "k."

Code

Abbreviations

Stockdale also talks of the pleasures of coming up with abbreviations, a necessity imposed by the time constraints on both the message giver and receiver. "Passing on abbreviations like conundrums got to be a kind of game," remembered Stockdale. "What would ST mean right after GN? 'Sleep tight,' of course. And DLTBBB? I laughed to think what our friends back home would think of us two old fighter pilots [Stockdale refers to Air Force Major Samuel Johnson, in an adjoining cell] standing at a wall, checking for shadows under the door, pecking out a final message for the day with our fingernails: 'Don't let the bedbugs bite.'" Some of the acronyms entered POW popular usage. One acronym, GBU, was used as a universal sign-off. It was shorthand for "God Bless You."

Source: Return with honor