Early developments

SOS

SOS is the commonly used description for the International Morse code distress signal (· · · — — — · · ·). This distress signal was first adopted by the German government in radio regulations effective April 1, 1905, and became the worldwide standard when it was included in the second International Radiotelegraphic Convention, which was signed on November 3, 1906, becoming effective on July 1, 1908. SOS remained the maritime distress signal until 1999, when it was replaced by the Global Maritime Distress Safety System.

From the beginning, the SOS distress signal has actually consisted of a continuous sequence of three-dits/three-dashes

In popular usage, SOS became associated with phrases such as "Save Our Ship" and "Save Our Souls". These were a later development, most likely used to help remember the correct letters (something known as a backronym).

Early developments

Before the development of radio communication in the early 1890s, seagoing vessels had already adopted a wide variety of visual and audio distress signals, using such things as semaphore flags, signal flares, bells, and foghorns. Radio—which initially was called "wireless telegraphy"—at first employed Morse code, the dit-and-dash system originally developed for landline telegraphy. With the introduction of shipboard radio installations, there was a need for standardized communication, but cooperation was somewhat limited by national differences and rivalries between competing radio companies.

The first International Radiotelegraphic Conference was held in Berlin, Germany in 1903. At the time, Captain Quintino Bonomo, an Italian representative, discussed the need for common operating procedures, including the suggestion that "ships in distress... should send the signal SSS DDD at intervals of a few minutes", according to "The Wireless Telegraph Conference", in the November 27, 1903, issue of The Electrician. However, procedural questions were beyond the scope of the 1903 Conference. Although Article IV of the Conference's Final Protocol, signed August 13, 1903, stated that "Wireless telegraph stations should, unless practically impossible, give priority to calls for help received from ships at sea," no standard signal was adopted at the time.

Because of the absence of international regulations, each ship was left to develop its own practices. For example in 1905 the crew of a sinking lightship off Nantucket transmitted the word "HELP" to call for rescue. Perhaps the first international radio distress call adopted was "CQD" (— · — · — — · — — · ·) which was announced on January 7, 1904 by "Circular 57" of the Marconi International Marine Communication Company, and which became effective for Marconi installations beginning February 1, 1904. Another suggestion appeared in the 1906 edition of S. S. Robison's "Manual of Wireless Telegraphy for the Use of Naval Electricians," published for use by the United States Navy. This stated that the standard visual flag signals, known as the International Code of Signals, would likely also be adopted for radio use. Thus, the flag signal "NC" (— · — · — ·), which stood for "In distress; want immediate assistance", would also likely become the radio distress call or a cry for help.

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