Tap Code

How to communicate covertly with someone else who knows the Tap Code: Tap on the floor, pipe, whistle; make any sound in the following sequence to send an alphabetic message.  This code has been around for awhile and was used most notably by US military personnel in the infamous “Hanoi Hilton” prison in North Vietnam.  Apparently unknown by their communist captors, Jane Fonda or John Kerry, the code was a significant asset and morale booster.

Hoa Lo Prison in Hanoi “The Hanoi Hilton”

Above: The entrance to the Hoa Lo Prison in Hanoi. Built by the French in the 1880’s, it is the infamous “Hanoi Hilton” where the communist government guards routinely beat and tortured US military personnel. (Reference 28) et. al.

How does the Tap Code work?

…….1       2        3        4        5

1     A       B      C/K     D        E

2     F       G       H        I         J

3     L       M       N       O        P

4     Q       R       S       T        U

5     V       W       X        Y       Z

That’s the letter matrix.  Simple, 25 letter grid of our 26 letter alphabet; using C instead of K is the only exception.    Any letter can be sent by tapping its matrix coordinates.  First tap(s) indicated the ROW NUMBER, second tap(s) indicates the COLUMN NUMBER of the letter to be sent.  Example:  The letter S would be sent:  tap tap tap tap  –  tap, tap, tap.  (Four taps, pause, three taps).   The word CODE tap sequence would be:  1,3   3,4    1,4    1,5.. The word COKE would be tapped 1,3   3,4   1,3   1,5  Your receiver would know the C/K substitution difference by context. You get it….[corrected!]

With practice, it can be memorized and sent-received quickly and efficiently.  It could even be sent by flashing a light.  US military personnel often sent it while sweeping, tapping the floor with a broom, among other means.   Why not Morse Code?  That would require the sending of “taps” with both long and short durations representing dashes and dots.  Difficult to do with simple tapping.  While knowledge of Morse Code is a basic military skill, few people these days are proficient with it, preferring cell phones and other gadgetry that won’t work when you really need it.

Hanoi Hilton Prison: Tap Code Demonstration

Hanoi Hilton Prison: Tap Code Demonstration


Above: Our buddy demonstrating the use of a broom to send Tap Code messages during our visit of the Hanoi Hilton prison. The potted plant and mat are presumably newer additions.  A very sinister place. But that’s a whole other story……

How do you remember the Code?  Good old Military Memory mnemonic trick:  The first column is AFLQVAir Force Loves Queer Virgins.  No offense – it’s how I was taught it (in the Navy!) – but it’s easy to remember!  (The Air Force probably has a different memory trick…see comment below!)  Once you’ve got that, the matrix fills itself out as shown.  Basic military knowledge – I even taught it to the Cub Scouts.  They had lots of practice with it in school.  (I recall that I used a different memory trick…)   Handy……Of course we use a different system now, but tuck this one away….