Tap Code

What is Tap Code?

Tap code is a cipher used to communicate by sounds, commonly associated with prisoners tapping on walls or pipes. It's based on the Polybius square, arranging the alphabet in a 5×5 grid where each letter is represented by two numbers—the row and column position.

History of Tap Code

Tap code became famous through its use by American POWs during the Vietnam War. Prisoners in the "Hanoi Hilton" used it to communicate through walls when speaking was forbidden. The code allowed them to maintain morale and share vital information.

How Tap Code Works

The alphabet (minus K, which is replaced by C) is arranged in a 5×5 grid:

1. Find the letter in the grid
2. Tap the row number
3. Pause briefly
4. Tap the column number
5. Longer pause before the next letter

Example: To send "HI"

• H = row 2, column 3 = tap tap (pause) tap tap tap
• I = row 2, column 4 = tap tap (pause) tap tap tap tap

Why K Becomes C

Since the 26-letter alphabet doesn't fit in a 5×5 grid (25 cells), one letter must be combined with another. K and C sound similar in many words, so K is replaced with C. Context usually makes the intended letter clear.

Tap Code in Geocaching

Geocaching puzzles use tap code because:

• Audio clues: Can be hidden in sound files
• Visual patterns: Dots or marks can represent taps
• Historical interest: POW connection adds meaning
• Physical element: Can involve actual tapping

Common Representations

Tap code can be written in various ways:

• Dots: .. ... (row dots, column dots)
• Numbers: 2,3 or 2-3 or (2 3)
• Tally marks: || ||| (vertical lines)
• Sounds: Actual audio recordings of taps
• Morse-like: Short and long signals

Tap Code Grid

Recognizing Tap Code

Look for these patterns:

• Paired groups: Patterns always come in pairs
• Range 1-5: No group larger than 5
• Dot patterns: Groups of dots with spaces
• Audio cues: Sound files with rhythmic tapping

Comparison with Morse Code