SOS Trivia History

The use of the SOS signal was first introduced in Germany as part of a set of national radio regulations, effective April 1 , 1905 . These regulations introduced three new Morse code sequences, including the SOS distress signal:
Ruhezeichen ("Cease-sending signal"), consisting of six dahs ( — — — — — — ), sent by shore stations to tell other local stations to stop transmitting.
Suchzeichen ("Quest signal"), composed of three-dits/three dahs/one-dit, all run together (• • • — — — • ), used by ships to get the attention of shore stations.
Notzeichen ("Distress signal"), consisting of three-dits/three-dahs/three-dits (• • • — — — • • • ), also in a continuous sequence, "to be repeated by a ship in distress until all other stations have stopped working".
SOS was developed from the general German radio call "SOE", with the 3 dits of a "S" easier to hear in under noisy conditions than the one dit of an "E". Also, the otherwise meaningless string of letters was selected because it is easily recognizable and can be sent rapidly. Comparing SOS (di-di-di-dah-dah-dah-di-di-dit) with the older CQD (dah-di-dah-dit dah-dah-di-dah dah-di-dit) (— • — • / — — • — / — • •) it is obvious how much simpler the new code was. Also, it would not be mistaken for CQ, the radio code for "calling anyone" used in casual circumstances.
In 1906, at the second International Radiotelegraphic Convention in Berlin, an extensive collection of Service Regulations were developed to supplement the main agreement, which was signed on November 3 , 1906 , becoming effective on July 1 , 1908 . Article XVI of the regulations adopted Germany's Notzeichen distress signal as the international standard, reading: "Ships in distress shall use the following signal: • • • — — — • • • repeated at brief intervals". The first ship to transmit an SOS distress call appears to have been the Cunard liner Slavonia on June 10 , 1909 , according to "Notable Achievements of Wireless" in the September, 1910 Modern Electrics. However, there was some resistance among the Marconi operators to the adoption of the new signal, and, as late as the April, 1912 sinking of the RMS Titanic , the ship's Marconi operators intermixed CQD and SOS distress calls. However, in the interests of consistency and public safety, the use of CQD appears to have died out after this point.
In both the April 1 , 1905 German law, and the 1906 International regulations, the distress signal was specified as a continuous Morse code sequence of three-dits/three-dahs/three-dits, with no mention of any alphabetic equivalents. However, in International Morse, three dits comprise the letter S, and three dahs the letter O. It therefore soon became common to refer to the distress signal as "SOS." An early report on "The International Radio-Telegraphic Convention" in the January 12 , 1907 Electrical World stated that "Vessels in distress use the special signal, SOS, repeated at short intervals." (In American Morse code , which was used by many coastal ships in the United States through the first part of the twentieth century, three dahs stood for the numeral "5", so in a few cases the distress signal was informally referred to as "S5S").
In contrast to CQD, which was sent as three separate letters with spaces between each letter, the SOS distress call has always been transmitted as a continuous sequence of dits-and-dahs, and not as individual letters. There was no problem as long as operators were aware that "SOS" was technically just a convenient way for remembering the proper sequence of the distress signal's total of nine dits and dahs. In later years, the number of special Morse symbols increased. In order to designate the proper sequence of dits-and-dahs for a long special symbol, the standard practice is to list alphabetic characters which contain the same dits-and-dahs in the same order, with a bar atop the character sequence to indicate that there should not be any internal spaces in the transmission. Thus, under the modern notation, the distress signal becomes SOS. (In International Morse, VTB, IJS and SMB, among others, would also correctly translate into the • • • — — — • • • distress call sequence, but traditionally only SOS is used).
SOS has also sometimes been used as a visual distress signal, consisting of three-short/three-long/three-short light flashes, or with "SOS" spelled out in individual letters, for example, stamped in a snowbank or formed out of logs on a beach. The fact that SOS can be read right side up as well as upside down became important for visual recognition if viewed from above.