SOS

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SOS is the commonly used description for the International distress signal (· · · — — — · · ·) as sent telegraphically in Morse code. The SOS distress signal first appeared when it was included in radio regulations adopted by the German government effective April 1, 1905. It became a worldwide standard when it was included in the regulations included with the second International Radiotelegraphic Convention, which was signed on November 3, 1906, and became effective on July 1, 1908.

The SOS distress signal, from its initial adoption, has consisted of a continuous sequence of three-dots/three-dashes/three-dots, without letter spacing. Because three dots form the letter S, and three dashes make the letter O, in International Morse Code, "SOS" became an easy way to remember the sequence of the dots and dashes. In popular usage, SOS became associated with phrases such as "Save Our Souls", "Save Our Ship", and "Stop Otheir Signals". However, these phrases were a later development, merely used to help remember the correct order of letters.

Initial suggestions

Radio communication — originally known as "wireless telegraphy" — did not exist prior to the mid-1890s. Before then, seagoing vessels adopted a number of visual and audio distress signals, including semaphore flags, signal lights and flares, bells, and foghorns. Although radio adopted the Morse code dot-and-dash system originally developed for land telegraphy, there was no standard distress call in use by landline telegraph operators.

After the development of shipboard radio installations, there was a need for standard communication practices, however, national differences and competition between rival radio companies limited cooperation. In 1903, the first International Radiotelegraphic Conference was held at Berlin, Germany. During this conferance, Captain Quintino Bonomo from Italy brought up the issue of the need for common operating standards, and in part suggested that "ships in distress... should send the signal SSS DDD at intervals of a few minutes". However, procedural issues were not a part of the Conference's mandate, the Conference did not adopt an official signal, although Article IV of the Conference's Final Protocol, signed August 13, 1903, did state that "Wireless telegraph stations should, unless practically impossible, give priority to calls for help received from ships at sea." Thus, individual governments and companies began to independently develop their own standards.

The first distress call to be adopted appears to have been "CQD", which was adopted by the Marconi International Marine Communication Company, announced on January 7, 1904 by the company's "Circular 57". CQD became effective for Marconi installations beginning February 1, 1904. In the 1906 edition of "Manual of Wireless Telegraphy for the Use of Naval Electricians" by S. S. Robison, which was used by the United States Navy, a section stated that the symbols used by International Code of Signals for visual signaling would also likely be adopted by the radio service. The visual flag signal "NC" stood for "In distress; want immediate assistance", and Robison suggested that this would also likely be adopted internationally as the distress call for radio operators.

1905: Germany creates SOS

National radio regulations announced by the German government in March, 1905, effective April 1, 1905, adopted three new Morse code sequences. This was the first appearance of the SOS distress signal:

  1. Ruhezeichen ("Cease-sending signal"), formed by six consecutive dashes ( — — — — — — ), used by shore stations to inform other local stations to stop transmitting.
  2. Suchzeichen ("Quest signal"), composed of three-dots/three dashes/one-dot, (· · · — — — · ), designed for transmitting to shore stations a ship's desire for attention.
  3. Notzeichen ("Distress signal"), consisting of three-dots/three-dashes/three-dots (· · · — — — · · · ), "to be repeated by a ship in distress until all other stations have stopped working".

A second International Radiotelegraphic Convention was held in Berlin in 1906, with a broader mandate. This body signed an international agreement on November 3, 1906, with an effective date of July 1, 1908. An extensive collection of Service Regulations was developed to supplement the main agreement, 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 about adopting 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. But with the need for consistency for public safety, the use of CQD largely disappeared 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-dots/three-dashes/three-dots, with no mention of any alphabetic equivalents. However, in International Morse three dots comprise the letter S, and three dashes the letter O, and it 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 dashes 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 dots-and-dashes, 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 dots and dashes. In later years, the number of special Morse symbols increased with the addition of numerous procedural signals. In order to designate the proper sequence of dots-and-dashes for these special symbols, the standard practice is to list alphabetic characters which contain the same dots-and-dashes in the same order, with the understanding that there are no internal spaces in the transmission of the special signal. It is also common practice to list procedural signals with a bar above the letters, thus, under this notation, the distress signal becomes SOS. (In International Morse, VTB, IJS and SMB, 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 makes visual recognition easier.

References

See also

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