The Vietnam Tap Code

Target Audience: Grades 7-12


  • Provide a brief history of Vietnam POWs
  • Support a discussion on the importance of communication between people in dire times
  • Teach the tap code to the group and have them use it to communicate with each other

Time: 30 minutes or one class period


1. Using the resources provided in the previous tab, give a brief history of American POWs in North Vietnam.

Discussion Points:

  • POW stands for Prisoner of War
  • 687 POWs returned after the Vietnam War, with North Vietnam acknowledging that 55 service members and 7 civilians died in captivity.
  • POWs were physically and psychologically tortured for propaganda purposes. The most famous of the six camps where they were imprisoned was Hỏa Lò Prison, also called Hanoi Hilton in North Vietnam.

Questions for Students:

  • During periods of combat, who would be the most likely to be captured? Why?

2. Students learn about the background of the tap code and hear from firsthand accounts.

Discussion Points:

  • Watch The Code produced by Airman Magazine
  • While Tap Code is the name given to the system that American POWs used in Vietnam, these type of knock codes have been around for centuries.
  • The tap code is based on the Polybius Square, named for the ancient Greek historian Polybius who recorded one of the first mentions of the knock codes between 200-118 BC. That’s more than 2,000 years ago!
  • The tap code system was first introduced to POWs in June of 1965, by Captain Carlyle Harris, Lieutenant Phillip Butler, Lieutenant Robert Peel, and Lieutenant Commander Robert Shumaker. Captain Harris recalled hearing about WWII POWs using knock codes and one of his Air Force instructors showed him the simple 5×5 grid code system. The four men used it among themselves until they were separated, which led to the spreading of the code.   
  • Prisoners were isolated, told not to talk, and punished for not following the rules. They were given very little food and water, tortured and questioned, with some dying due to the torture and malnutrition. Ultimately, the main reason North Vietnam tortured the American POWs was to break their spirit and force them to appear on television or media to discredit the United States’ war effort.

Questions for Students:

  • Why is this type of secret communication important?
  • What does this tell us about those who were taken prisoner?

3. Return to the discussion of why communicating between POWs was important.

  • From Tap Code: The Epic Survival Tale of a Vietnam POW and the Secret Code that Changed Everything, “First and foremost, it was a great morale booster, and it helped us maintain our sanity. If a POW felt totally alone, without any communication with those who were experiencing the same tragic existence, his mental and emotional capabilities were severely vulnerable.
  • Communication also helped us order our ranks within the camp. Through tapping or whispering, we were able to discern who was in top command of our POWs. We still adhered to the order of command, which often helped us resist the enemy as a united force.” – Col. Carlyle Harris (Ret.)
  • Refer to the military Code of Conduct on the next tab for information about what was expected from members of the Armed Forces if they were captured.

Do the first part of the “Shave and a Haircut” jingle and see if any students respond with the final two knocks.

  • To signal that someone wanted to start a conversation, POWs would open with the “Shave and a Haircut” jingle, waiting for the last two knocks as a response that the other person was ready.

Explain the Tap Code Grid

  • The 5×5 grid system is separated by rows and columns.
  • There is no letter K, instead C is used.
  • The first series of taps indicates the row number, the second series of taps indicates the column. Memorizing the first column is the only thing necessary as long as you know the alphabet.
  • Once you know if it’s A, F, L, Q, or V you follow the alphabet out from that letter for the second series of knocks.
  • The letter X was used as the period or to separate sentences.

Provide an example of a message (Try “NVMM”).

Questions for Students:

  • What connections can you make to how you communicate today?
  • Do you have a secret way of communicating with a sibling or friend?

Practice, Practice, Practice!

  • Students pass messages to each other using the tap code.
  • Students practice using the code with the examples provided.
  • Students can sit back-to-back with one student tapping while the other translates using the 5×5 grid.
  • Space out the students so they aren’t distracted by the tapping of other groups.
  • One student could tap on the door to the classroom, while the entire group translates.
  • The student translating can write the words on the back of their grid or a blank sheet of paper.

The Code of Conduct applies to all members of the U. S. Armed Forces, at all times.

I am an American fighting in the forces that guard my country and our way of life, I am prepared to give my life in their defense.

I will never surrender of my own free will. If in command, I will never surrender the members of my command while they still have means to resist.

If I am captured, I will continue to resist by all means available. I will make every effort to escape and aid others to escape. I will accept neither parole nor special favors from the enemy.

If I become a prisoner of war, I will keep faith with my fellow prisoners. I will give no information nor take part in any action which might be harmful to my comrades. If I am senior, I will take command. If not, I will obey the lawful orders of those appointed over me and will back them up in every way.

Should I become a prisoner of war, I am required to give name, rank, service number, and date of birth. I will evade answering further questions to the utmost of my ability. I will make no oral or written statements disloyal to my country and its allies.

I will never forget that I am an American fighting for freedom, responsible for my actions, and dedicated to the principles which made my country free.

I will trust in my God and in the United States of America.
The Code of Conduct

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