Regarding: What does "SOS" mean?


I offer an alternative theory.

Prior to telegraphs, trains used a system of whistle signals consisting of short or long blasts. Three long - Danger … three short - Apply Brakes. Often “Apply Brakes” would be issued in a set of three to signal an emergency. Telegraph operators were familiar with the train whistle signals. As wireless telegraphy began to be used on ships, these same people from railroad backgrounds came to operate them. Several telegraphy codes existed at this time… Morse, ABC Universal Code, Philips ( that I am aware of, and probably others ). An exclamation point in Morse is 3 dashes, 1 dot (an “5” with a dot in Morse itself, in ABC Universal code “O” with a dot ), an exclamation in ABC Universal code is 2 dashes, 2 dots, 2 dashes. I propose the telegraph operators incorporated the ABC Universal code for exclamation point with the train whistle signals, since three sets of “Apply Brakes” was already a well-known signal for emergency.

The linked-to Staff Report provides an amusing walk through folk etymology, but should not be considered to be factually correct. (A discussion when the column originally appeared is at: )

In addition, I haven’t seen any theories that the SOS distress call originated from land telegraph practices. There is, however, some evidence that CQD, adopted by the Marconi companies in 1904, may have had its roots in British land telegraphy, as CQ reportedly was an “all stations” call. The D was then added for radio use to make the distress call – it is usually thought to stand for “Distress”.

Since nothing has changed, I’ll repeat the corrections about SOS that I posted 11 years ago. Quotes from the Staff Report are in italics:

In fact, SOS in not an acronym and it doesn’t represent anything at all.

It should also be stressed that, unlike CQD, the “SOS” distress signal really isn’t even three letters. From the beginning it has officially been …—… or three dots/three dashes/three dots all run together as a single entity. If you informally divide it into three equal parts it becomes “SOS” in Continental Morse code. However, in American Morse code, which was used by many U.S. ships through the first part of the twentieth century, — stood for the numeral “5”, so in this case the international distress signal was informally referred to as “S5S”. (See Francis A. Collins’ 1912 Some Stirring Wireless Rescues for more details.)

In 1908, an international committee tried to come up with a distress signal that would be easy to remember during a crisis, and could be transmitted by an amateur with only rudimentary knowledge of Morse Code. They decided a simple combination of threes: three letters, each represented by three marks, since three is a universally favored number. Well, at least in Western cultures.

The “SOS” distress signal actually dates back to at least April 1, 1905, when it was adopted by a national German law. (See Regelung der Funkentelegraphie im Deutschen Reich and German Regulations for the Control of Spark Telegraphy. It was next adopted as the international standard by the Berlin International Wireless Telegraph Convention, which was signed on November 3, 1906, and became effective on July 1, 1908. (See 1906 International Wireless Telegraph Convention/Service Regulation XVI.)

In Morse Code, the only letters represented by three identical marks are O (three dashes) and S (three dots). The committee toyed with OSO, but dashes are longer electrical signals to transmit than dots. An urgent message needed to be broadcast as quickly as possible and use as little power as possible, and so SOS became international standard.

I don’t know where this “committee” story comes from, but the simplest explanation is that the Convention merely adopted the distress signal that had already been in use in Germany for the past year-and-a-half. I’ve never seen any references to “OSO” being considered. And amateur operators certainly weren’t a factor, as they essentially didn’t exist in 1905/1906, and anyway, according to the 1906 Convention the distress signal was adopted for use by “ships in distress”.

Interesting idea, Kaulbach. You made that up, right?

a short repeated signal is attention getting. its use for emergency, in rail or otherwise, is somewhat intuitive.

in telegraphy, especially wireless, a dit [dot] (short signal) could be caused in error or because of malfunction (e.g. loose connection). so even a repeated series of dits might be meaningless. a repeated mixture of dits [dot] and dahs [dash] would have to be taken as intended purposeful communication. as Dex stated in the column SOS could be easily remembered and performed by a unexperienced person.

i don’t think rail telegraphers would be recruited to become wireless operators at sea because of their knowledge of telegraphy. ship wireless operators would need to know electronics in order to operate and maintain the wireless equipment. the ability to serve on a ship and operate wireless apparatus were of extreme importance.

The problem with most electricians was they didn’t know Morse code and weren’t experienced with the specialized equipment used for radio. You really needed training in both areas, such as what was offered (in 1917) by Dodge’s Telegraph, Railway Accounting and Radio (Wireless) Institute of Valparaiso, Indiana: