Tap Code Encoder & Decoder – POW Communication Tool

Tap Code is a simple cipher communication method that uses a 5×5 grid (Polybius square) to encode letters. Each letter is represented by two numbers: its row and column in the grid. To transmit a letter, you tap the row number, pause briefly, then tap the column number. For example, A (row 1, column 1) = . . (one tap, pause, one tap). H (row 2, column 3) = .. ... (two taps, pause, three taps).

The standard Tap Code uses a 5×5 grid which has only 25 cells, but the English alphabet has 26 letters. To fit all letters, C and K share the cell at position (1,3). When encoding, both C and K produce the same tap pattern (. ...). When decoding, context usually determines which letter is intended. Some variations omit J instead, but the C/K combination is the most widely accepted standard.

During the Vietnam War, American prisoners of war famously used Tap Code to communicate between cells by tapping on walls or pipes. Captain Carlyle "Smitty" Harris is credited with introducing the system after recalling it from a survival course. It became a lifeline for isolated prisoners, allowing them to share information, boost morale, and coordinate resistance. The code was simple enough to remember under duress and could be transmitted through any solid surface.

While both use patterns of taps, they are fundamentally different systems. Morse Code uses short and long signals (dots and dashes) with variable-length patterns for each letter. Tap Code always uses exactly two groups of taps per letter (row then column), each group containing 1–5 taps. Tap Code is generally easier to learn quickly since it relies on a simple grid reference rather than memorizing unique patterns for each letter. This made it ideal for distressed POWs who needed a reliable communication method.

Here are some recognizable patterns:

• SOS – .... ... / ... ... / .... ... (S=4,3; O=3,4; S=4,3)
• HELLO – .. ... / . ..... / ... .. / ... .. / ... ...
• OK – ... ... / . ... (O=3,4; K=1,3 → C/K cell)
• A – . . (simplest pattern: 1 tap, pause, 1 tap)
• Z – ..... ..... (longest pattern: 5 taps, pause, 5 taps)

Traditional Tap Code only encodes the 26 letters A–Z using the 5×5 grid. Numbers, punctuation marks, and special characters are not part of the original system. In practice, POWs would spell out numbers as words (e.g., "TWO" instead of "2") or use contextual abbreviations. Some extended versions add a 6×6 grid to include digits, but this deviates from the classic POW Tap Code standard. Our tool focuses on the classic 5×5 system and will ignore or flag non-letter characters during encoding.

Our decoder is flexible and accepts multiple formats:

• Dot format: .. ... / . ..... (dots represent taps, spaces separate row from column, slashes separate letters)
• Number format: 2,3 1,5 or (2,3)(1,5) (comma-separated row,col pairs)
• Mixed separators: You can use /, |, newlines, or spaces between letter codes
• Flexible spacing: Extra spaces are handled gracefully