Dear doc_comfort: I don't remember for sure, but think it was indeed chosen for its
easy sending and recognition. It was an International signal, and as acronym would have
no value to the very large number of vessels operated by non-English speakers.

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From www.arrl.org
SOS

The amateur distress call, QRRR, grew from the purpose of the first organized amateur emergency nets. They were set up in
cities along the Pennsylvania Railroad to aid the "Pennsy" (and later other railroads) with train communications in the event of
failure of the railroad telegraph landlines--which were frequent. The signal QRR came to be used to indicate that the calling
station had railroad traffic related to some emergency. ARRL eventually adopted this call for use by any amateur who had
distress traffic and later the call was changed to QRRR because of a conflict in definitions with the international Q signal QRR.

One of the first distress calls was CQD, coined by the Marconi Company about 1904 from the "general call" CQ and the letter
D for "distress." The main problem with CQD was that it was supposed to be used only by ships which subscribed to the
Marconi radio system and ships of one system were discouraged from communicating with ships or shore stations of other,
competing, companies. The problem got so bad that it was taken up in the international radio conference in 1906 where a new
universal distress call was proposed.

The American delegation suggested the letters NC which were already recognized in the International Signal Code for Visual
Signalling. The German delegation proposed its own SOE which was already in use on German ships as a general inquiry signal
similar to CQ (which was then used only by the Marconi system). The British delegation, of course, wanted to stick to the
Marconi signal CQD.

The convention found SOE acceptable except that the final E could easily be lost in QRN so the letter S was substituted,
making it SOS. The convention decided that SOS should be sent as a single code character with a sound unlike any other
character, thus arresting the attention of anyone hearing it. So was officially adopted, but CQD remained in use for some years,
particularly aboard British ships.

It wasn't until 1912, after the Titanic disaster, that SOS became universal and the use of CQD gradually disappeared. Titanic
radio operator Jack Phillips sent both CQD and SOS to be sure that there couldn't possibly be any misunderstanding.

[SOS does not stand for Save Our Ship or Save Our Souls - Ed.]

Mayday

Incidentally, another distress call is used by aircraft in trouble throughout the world. We have all heard the term "mayday" at
some time. This, of course, has nothing to do with the first day in May. As it turns out, in French, the word "m'aidez" means
"help me". Is it possible that American aviators in World War I picked this up from their French comrades and mispronounced
it as the easily recognized "mayday, mayday"?