American Morse code vs International Morse code
American Morse is the original telegraph code of the United States, used on landlines and railroads, and it has spaces inside some characters and extra-long dashes for L and the figure 0. International Morse, also called Continental, is the later, more regular code used on radio and taught today, with just two element lengths and fixed gaps. If you are learning Morse now, learn International: it is the one in the ITU standard, on the amateur bands and in every chart you are likely to meet.
The two share a name and a lot of letters, but they are different codes, and a chart for one will mislead you on the other.
How American Morse is built
International Morse has a strict, simple grammar. There are two sounds, the dit and the dah, and three silences: 1 unit inside a character, 3 between characters and 7 between words, as set out in ITU-R M.1677-1.
American Morse, the landline or railroad code, allows more:
- Spaces inside characters. C, O, R, Y, Z and the ampersand are each made of dots with a pause inside the character. The receiver has to tell that inner pause from the gap between two letters.
- Long dashes. L is a single long dash, and the figure 0 a longer one still. The receiver has to tell a dash from a long dash by its length alone.
Here are the characters that differ in shape. American Morse is written out in words, because its inner pauses do not fit the notation used for International Morse:
| Character | International | American Morse |
|---|---|---|
| C | -.-. |
two dots, a pause, one dot |
| O | --- |
one dot, a pause, one dot |
| R | .-. |
one dot, a pause, two dots |
| Y | -.-- |
two dots, a pause, two dots |
| Z | --.. |
three dots, a pause, one dot |
| & | .-... |
one dot, a pause, three dots |
| L | .-.. |
one long dash |
| 0 | ----- |
one longer dash |
The ampersand .-... is not in the ITU standard, but it is the code commonly used for it in International Morse.
Several other letters and most of the figures also have different codes in the two systems, so the table is not the whole difference. It shows only the features that make American Morse American.
Why the spaced letters are hard
Look at the American O: a dot, a pause, a dot. In International Morse a dot, a letter gap and a dot is simply E E. The two differ only in the length of one silence, and that silence is set by the sender’s hand.
The same trap catches every spaced character. Read with International ears, the American C sounds like I E, R like E I, Y like I I, Z like S E and the ampersand like E S. On a quiet wire with a skilled sender, operators learned to hear the difference. On a weak or fading signal, or with a hurried hand, it is easy to get wrong.
International Morse avoids the problem by design. Inside a character, every gap is the same 1 unit, so any longer silence always means a new letter. And there are only two lengths of sound, so you never have to judge whether a dash is a long one. This is the reason usually given for the revision that produced the International code.
Why the two codes split
The code that came out of Samuel Morse and Alfred Vail’s work in the 1830s and 1840s is the ancestor of American Morse, and it spread with the telegraph across the US. Who invented Morse code? Samuel Morse and Alfred Vail covers how that code came about.
When Morse’s system was taken up in Europe, its code was reworked. The International code is usually traced to Friedrich Clemens Gerke’s revision of 1848. From there the paths divided:
- American Morse stayed on American wires. Landline and railroad telegraphers in the US used it, mostly by ear on a sounder. A sounder makes no tone, only a click as its lever goes down and another as it comes up, so a dot or a dash is the time between two clicks. How the electric telegraph worked: keys, sounders and relays explains the instruments.
- International Morse went to radio. It became the code of wireless, and so of ships, of the SOS distress signal adopted at Berlin in 1906, of aviation beacons and of amateur radio. Heard on radio, it is a tone switched on and off, not a click.
As landline telegraphy faded, American Morse went with it. International Morse is the code that lasted, and it is the one the ITU keeps as the standard today.
Which one should you learn?
For almost everyone, International Morse. Here is why:
- It is the standard. The ITU defines its letters, figures, punctuation and timing in ITU-R M.1677-1. Every serious chart follows it.
- It is what you will hear. Amateur radio CW, aviation beacon identifiers and signal lamps at sea all use International Morse.
- Its timing is regular. One unit inside a character, three between characters, seven between words. Once your ear has the rhythm, there is nothing else to judge.
- Almost everything for learners uses it. Courses, practice files and drills are written for International Morse.
Learn American Morse if you have a reason to: an interest in railroad and landline telegraph history, a period sounder you want to read, or a museum display you want to understand. A few telegraph hobbyists still use it on sounders. If you do learn both, learn International first and keep the American letters for when you are listening to a sounder, since several of them would otherwise collide with codes you already know.
If you practice on a Mac, Dot & Dash teaches and plays International Morse only: letters, figures, everyday punctuation and the common prosigns, timed to the PARIS standard. It has no American Morse table, so it is a good fit for the code you are likely to use and no help with the railroad one.
Telling which code you are looking at
If you come across Morse in an old document, a museum or a film and cannot tell which code it is in, a few signs help:
- Visible spaces inside a character, or dashes of more than one length, mean American Morse.
- A run of short letters that makes no sense when read as International, such as E E, I E, E I or I I where a word should be, often means American O, C, R or Y read with the wrong chart.
- A tone and a radio setting mean International. Clicks from a sounder on a US railroad or landline mean American is likely.
- Anything from radio, ships or aviation, or anything containing SOS sent as one character,
...---..., is International.
The Morse code alphabet from A to Z gives the full International table, with the rhythm of each letter, if you need it to check.
Questions
Is American Morse code still used?
Rarely. It belonged to landline and railroad telegraphy, which has faded, though a few telegraph hobbyists still use it on sounders. Radio, ships, aviation and amateur operators use International Morse.
Is Continental code the same as International Morse?
Yes, Continental is another name for International Morse, the code that grew out of European revisions of the American code.
Which Morse code is SOS in?
International Morse. SOS was adopted at the 1906 International Radiotelegraph Convention in Berlin and is sent as one continuous character, ...---....
Can I learn American Morse after International?
Yes, but expect some confusion at first: the American spaced letters sound like pairs of International letters, and several other characters have different codes. Keep the two apart by context, sounder for American and tone for International.