I am fairly sure that I have read (probably in a 1950:s edition of the Swedish navy soldier’s handbook "Örlogsboken"), that "tap morse", for example for communication with persons trapped inside a damaged ship, is done by tapping once for a dit, and twice in rapid succession for a "dah".
> Recently there was real-life incident, the Titan submersible accident which started speculation about a banging noise being Morse Code. When the submersible imploded over 3,800 meters below the surface, the resulting sound was heard as a loud bang by the crew of a passing ship. Conspiracy theories quickly emerged suggesting that the bang was Morse code, a desperate attempt for help from the doomed submarine. However, experts dismissed this idea, explaining that the sound was unrelated.<p>What kind of game of telephone led to this? The periodic banging noises were reported on Wednesday[0]. Rescue ships heard these noises. The sub had imploded on the previous Sunday. To my knowledge, no passing ship heard the implosion; it was detected by US Navy sensors. The #1 thing reported about the banging noises was that they were coming at 30 minute intervals. Obviously the submarine imploded only once.<p>Nobody mistook the implosion of the submarine for Morse code - the banging noises were some other third thing. This paragraph must have been the product of substantial confusion.<p>[0] For example: <a href="https://nypost.com/2023/06/21/glimmer-of-hope-30-minute-intervals-between-banging-noises-encouraging-sign-titan-crew-still-alive/" rel="nofollow noreferrer">https://nypost.com/2023/06/21/glimmer-of-hope-30-minute-inte...</a>
During (what we Americans call) the Vietnam War, American prisoners of war, often held in solitary confinement in adjacent cells in the Hanoi Hilton, would use the tap code extensively to talk to each other, sometimes carrying on long conversations, for example about ways to resist their captors. The article alludes to that but doesn't go into a lot of detail about that bit of history.<p>(This is discussed in <a href="https://en.wikipedia.org/wiki/Tap_code" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/Tap_code</a> cited downthread by 'dmckeon.)
This is article is a pedantic waste of time.<p>Tapping out SOS is a thing… <a href="https://www.smithsonianmag.com/history/the-civilian-worker-who-spearheaded-pearl-harbors-most-successful-rescue-mission-180979167/" rel="nofollow noreferrer">https://www.smithsonianmag.com/history/the-civilian-worker-w...</a>
Anecdotally, I clicked the article, read nothing, and immediately listened to the first sound clip where I was able to make-out that it represented "CQ", but to be fair I'm a ham and "CQ" is by-far the most common morse code message.<p>All you need is a ternary system where there is dit, dah, and silence. Even just tapping on different parts of the "wall" can serve this purpose, so long as it is able to be differentiated.
The argument is pedantic. It may not be Morse, but it's definitely possible to communicate by tapping on the wall. Imagine tapping out all of <i>Anna Karenina</i> to save a fellow inmate's life.<p><a href="https://www.npr.org/2017/09/11/550058353/rough-translation-how-anna-karenina-saved-a-somali-inmates-life" rel="nofollow noreferrer">https://www.npr.org/2017/09/11/550058353/rough-translation-h...</a><p><a href="https://www.bbc.co.uk/programmes/p03ttfks" rel="nofollow noreferrer">https://www.bbc.co.uk/programmes/p03ttfks</a><p>One of my college classes was network communications and for a group project, we had to devise how to transmit a binary message visually standing across from each other by 100 yards or so. Four people to a group, split two and two.<p>The idea was to get us to strike a balance between speed of encoding/decoding, ability to distinguish symbols, and how many bits to encode in each symbol.<p>I think my group came up with a system to transmit 3 bits at a time which failed spectacularly on the windy day we had for showing it off. My recollection is we had a big box with neon colored flaps that we could fold in/out.<p>I wish we'd researched prior works of art. To this day, I have no idea why we didn't just learn flag semaphores. Maybe there was a rule against using existing systems though?
Morse SOS:<p>bang-bang-bang---bang---bang---bang---bang-bang-bang<p>While Morse in general has problems with just banging, with SOS it is not a problem.
Disagree.<p>I'm a ham; my kids aren't... but they grew up with me using Morse (my computers talk to me when they boot up, and when a 'kitchentimer' goes off, and...) so they were naturally exposed to the paradigm. Maybe that's a limiting factor, but...<p>With CW you're limited to two states: key and unkey. Knocking on a wall, you're not: you can go loud and soft as well. A dah has the same pacing as it always does (3 dits in length), but if its knock is perceptibly louder, at least twice as hard as a dit, in practice that seems to make it hold together as readable Morse, at least for us. Certainly our family signal, questionmark (..__..), is usable that way, so is each son's "call-letter".
So sad to read the misleading stuff here.<p>The original morse sounders used a large relay which went "Click" when operated and another "Click" when released. (some will argue that it's "Click-Clack", but that makes no difference)<p>So a Dit sounds like Click/Click, while a Dah sounds like Click ..... Click.<p>Which is how only one sound (plus spaces) can encode morse.<p>In other words it's all in the rhythm of the sounds.<p>Years ago, divers were taught to send morse by holding a spanner in their fist, and rocking it back and forth against the hull (eg click/click) in exactly the same way as the armature in an original morse sounder operated.<p>And yes, there is also a completely different system called the "Tap Code".
The only Morse code message I know is SOS which is ...---... and I imagine it's reasonably easy to understand when being tapped in an emergency situation. It would tell rescuers that someone is still alive and to continue their search.
There's a lot of commentary here about Morse code being <i>possible</i> by tapping on a wall, which it is if and only if <i>both sender and receiver are already trained in Morse</i>. Problem is, your average prisoner isn't, the encoding is not at all obvious (because it's designed for speed of use, not ease of learning), and they can't just look up it up on Wikipedia when in solitary confinement,<p>This is why simpler tap codes exist: A = 1 tap, B = 2 taps etc is self-evident, and from there it's only a small leap to the Polybius square 5x5 tap code covered in Wikipedia.
For those who still don't understand how the Telegraph uses simple clicks to encode the alphabet....<p>Download "Morse Code Tools" from <a href="https://morse-code-tools.software.informer.com/2.1/" rel="nofollow noreferrer">https://morse-code-tools.software.informer.com/2.1/</a><p>Then run "Morse Keyer" and select "Straight Key" and "Telegraph Sounder"<p>You can hear exactly how a Morse Telegraph sounded back in the day<p>Two clicks per element, with different spacings between them.<p>Likewise run the "Morse news" program to hear some text.
It's worth noting that during the American civil war many telegraph operators used something called dot code, which consisted of clusters of 1-3 taps that corresponded to a contemporary flag signal code. That could certainly be transmitted through a wall. Likewise, you could probably slow down morse and transmit long pulses as clusters of 2 quick taps if you wanted to reuse that code on a wall.
One the most interesting uses of morse code was a Vietnam POW blinking the word "torture" during an interview.<p>See here for the interview: <a href="https://www.youtube.com/watch?v=rufnWLVQcKg">https://www.youtube.com/watch?v=rufnWLVQcKg</a>
I don’t know if I agree with the author’s conclusion that you can’t differentiate Morse dit and dahs tapped on a pipe.<p>That’s assuming that your listener has no brain and can’t figure out what the longer pauses between your taps mean.