# Tapping Morse code: Huh? **URL:** \ **Category:** Factual Questions\ **Created:** [April 23, 2024, 6:26pm UTC](https://boards.straightdope.com/t/tapping-morse-code-huh/1000667 "2024-04-23T18:26:02Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Schnitte](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/schnitte/32/9033_2.png) [@Schnitte](https://boards.straightdope.com/u/Schnitte)\ **Post date:** [April 23, 2024, 6:26pm UTC](https://boards.straightdope.com/t/tapping-morse-code-huh/1000667/1 "2024-04-23T18:26:02Z")
This is a common trope in films: The hero, incarcerated by the villain or otherwise trapped in an enclosed space, uses knocks to communicate with the outside world via Morse code. How is this supposed to work, assuming it was ever used in practice? Morse code consists of short signals (dots), long signals (dashes), and silence (pauses). When I knock a solid surface, it makes one singular tapping sound; I can’t control the length of the sound. Is it that the sender marks not the signal itself but the end of the signal, so that two knocks in quick succession mean a dot and two knocks with a longer break between them would mean a dash? ---
**Author:** ![Dr.Drake](https://avatars.discourse-cdn.com/v4/letter/d/ad7895/32.png) [@Dr.Drake](https://boards.straightdope.com/u/Dr.Drake)\ **Post date:** [April 23, 2024, 6:30pm UTC](https://boards.straightdope.com/t/tapping-morse-code-huh/1000667/2 "2024-04-23T18:30:17Z")
Yes: you can control the length of the pause. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [April 23, 2024, 6:31pm UTC](https://boards.straightdope.com/t/tapping-morse-code-huh/1000667/3 "2024-04-23T18:31:22Z")
I do not know Morse code, but I’m familiar with how it is portrayed as you describe in films. Basically, you leave a longer interval between the dashes than you do the dots. For example, SOS: knock, knock, knock [pause] knock… knock… knock [pause] knock, knock, knock ---
**Author:** ![Pardel-Lux](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pardel-lux/32/20182_2.png) [@Pardel-Lux](https://boards.straightdope.com/u/Pardel-Lux)\ **Post date:** [April 23, 2024, 6:45pm UTC](https://boards.straightdope.com/t/tapping-morse-code-huh/1000667/4 "2024-04-23T18:45:07Z")
That is also the way I understand it is done. And you don’t even have to tap, you can do it by blinking! > **[Watch The Video Of An American POW In Vietnam Blinking A Desperate Warning In...](https://www.ranker.com/list/video-of-vietnam-pow-blinking-morse-code/cleo-egnal)** > > Jeremiah Denton was a commander in the United States Navy during the Vietnam War when he was shot down, injured, and then taken prisoner by the North Vietnamese. Denton endured torture and solitary confinement as a POW at the hands of his... ---
**Author:** ![Llama\_Llogophile](https://avatars.discourse-cdn.com/v4/letter/l/49beb7/32.png) [@Llama\_Llogophile](https://boards.straightdope.com/u/Llama_Llogophile)\ **Post date:** [April 23, 2024, 6:46pm UTC](https://boards.straightdope.com/t/tapping-morse-code-huh/1000667/5 "2024-04-23T18:46:33Z")
A tap code is not necessarily Morse Code: > **[Tap code](https://en.wikipedia.org/wiki/Tap_code)** > > The tap code, sometimes called the knock code, is a way to encode text messages on a letter-by-letter basis in a very simple way. The message is transmitted using a series of tap sounds, hence its name. > The tap code has been commonly used by prisoners to communicate with each other. The method of communicating is usually by tapping either the metal bars, pipes or the walls inside a cell. > The tap code is based on a Polybius square using a 5×5 grid of letters representing all the letters of the L... ---
**Author:** ![Skywatcher](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/skywatcher/32/254_2.png) [@Skywatcher](https://boards.straightdope.com/u/Skywatcher)\ **Post date:** [April 23, 2024, 6:57pm UTC](https://boards.straightdope.com/t/tapping-morse-code-huh/1000667/6 "2024-04-23T18:57:46Z")
As noted in that tap code article, another way to make dashes distinguishable from dots is to make the dashes _louder_. ---
**Author:** ![kk\_fusion](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kk_fusion/32/15276_2.png) [@kk\_fusion](https://boards.straightdope.com/u/kk_fusion)\ **Post date:** [April 23, 2024, 7:14pm UTC](https://boards.straightdope.com/t/tapping-morse-code-huh/1000667/7 "2024-04-23T19:14:24Z")
One of my professors claimed to have done it, while imprisoned in the GDR around 1980. Him and other political prisoners communicated by sending Morse code through the heating pipes. ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [April 23, 2024, 7:27pm UTC](https://boards.straightdope.com/t/tapping-morse-code-huh/1000667/8 "2024-04-23T19:27:34Z")
> [@Llama\_Llogophile](#): > > A tap code is not necessarily Morse Code: Good point. In the early days of the US-Viet Nam war, US POWs improvised that code as described in the article. One or two people knew it from classical studies and they taught it to everyone else imprisoned at the time. Then it was taught to each newly arriving prisoner. Which teaching was itself a difficult task. One of the many lessons that DoD learned from Viet Nam was the value in training at least aircrew, and some especially behind-the-lines ground troops, e.g. Special Forces, how to be a successful POW. And to have all the services teaching the same tricks, techniques and basic doctrine. By the time I was going through USAF tactical pilot training ~10 years after US involvement in Viet Nam ended all that stuff was routine. Which was a real help in captivity. ---
**Author:** ![Horatius](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/horatius/32/3572_2.png) [@Horatius](https://boards.straightdope.com/u/Horatius)\ **Post date:** [April 23, 2024, 7:48pm UTC](https://boards.straightdope.com/t/tapping-morse-code-huh/1000667/9 "2024-04-23T19:48:56Z")
> [@Skywatcher](#): > > As noted in that tap code article, another way to make dashes distinguishable from dots is to make the dashes _louder_ Also, if you have an object you can use for tapping, instead of just your hand, I’ve seen tap and scratch codes. Tap for a dot, scratch for a dash. Really, so long as you can distinguish two different signals, you can do Morse. ---
**Author:** ![Skywatcher](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/skywatcher/32/254_2.png) [@Skywatcher](https://boards.straightdope.com/u/Skywatcher)\ **Post date:** [April 23, 2024, 8:10pm UTC](https://boards.straightdope.com/t/tapping-morse-code-huh/1000667/10 "2024-04-23T20:10:12Z")
> [@Horatius](#): > > Also, if you have an object you can use for tapping, instead of just your hand, I’ve seen tap and scratch codes. Tap for a dot, scratch for a dash. One of the books in the [Wings of War series](https://www.goodreads.com/series/103148-wings-of-war) utilizes similar for sequences set in [Hỏa Lò.](https://en.wikipedia.org/wiki/H%E1%BB%8Fa_L%C3%B2_Prison) The author has a POW passing messages with a push broom, alternating between sweeping and tapping. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [April 23, 2024, 9:11pm UTC](https://boards.straightdope.com/t/tapping-morse-code-huh/1000667/11 "2024-04-23T21:11:02Z")
> [@LSLGuy](#): > > By the time I was going through USAF tactical pilot training ~10 years after US involvement in Viet Nam ended all that stuff was routine. Which was a real help in captivity. That last sentence seems to imply that you were in captivity? ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [April 24, 2024, 2:08am UTC](https://boards.straightdope.com/t/tapping-morse-code-huh/1000667/12 "2024-04-24T02:08:45Z")
I was never an actual captive or POW. Sorry to be unclear. However the services run a POW training program for aircrew which includes a few days of simulated captivity. Which everybody goes through. Not much more can be said by the participants, but see here for more: > **[Survival, Evasion, Resistance and Escape](https://en.wikipedia.org/wiki/Survival,_Evasion,_Resistance_and_Escape)** > > Survival, Evasion, Resistance, and Escape (SERE) is a training program, best known by its military acronym, that prepares U.S. military personnel, U.S. Department of Defense civilians, and private military contractors to survive and "return with honor" in survival scenarios. The curriculum includes survival skills, evading capture, application of the military code of conduct, and techniques for escape from captivity. Formally established by the U.S. Air Force at the end of World War II and the...