Editing SOS (section)

==History==
[[File:Thesos.jpg|thumb|300px|{{sc|SOS}} was introduced for emergency maritime radio communication using [[Morse code]].|alt=]]

Radio (initially known as "wireless telegraphy") was developed in the late 1890s, and was quickly recognized as an important aid to maritime communication. Previously, seagoing vessels had adopted a variety of standardized visual and audio distress signals, using such things as semaphore flags, signal flares, bells, and foghorns. However, cooperation in standardizing radio distress signals was initially limited by national differences and rivalries between competing radio companies.

In 1903, an Italian representative at the Berlin [[Preliminary Conference on Wireless Telegraphy]], Captain Quintino Bonomo, 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".<ref>{{cite journal |title=The Wireless Telegraph Conference |journal=[[The Electrician]] |date=27 November 1903 |page=214 |url=https://babel.hathitrust.org/cgi/pt?id=njp.32101050973369&view=1up&seq=236}}</ref> However, procedural questions were beyond the scope of this conference, so no standard signal was adopted at the time, although Article&nbsp;IV of the conference's ''Final Protocol'' stated that "Wireless telegraph stations should, unless practically impossible, give priority to calls for help received from ships at sea".<ref>{{cite book |first=Linwood S. |last=Howeth |year=1963 |section=Appendix&nbsp;B: ''Final Protocol'', Article&nbsp;IV |department=First International Radio Telegraphic Conference, Berlin, 1903 |title=History of Communications-Electronics in the United States |page=547 |section-url=https://babel.hathitrust.org/cgi/pt?id=uiug.30112064674325&view=1up&seq=579}}</ref>

Without international regulations, individual organizations were left to develop their practices. On 7&nbsp;January 1904 the [[Marconi Company|Marconi International Marine Communication Company]] issued "Circular&nbsp;57", which specified that, for the company's worldwide installations, beginning 1&nbsp;February 1904 "the call to be given by ships in distress or in any way requiring assistance shall be [[CQD|C.Q.D.]]"<ref>{{cite book |first=G.E. |last=Turnbull |section=Distress signalling |year=1913 |title=The Yearbook of Wireless Telegraphy and Telephony |pages=318–322 |section-url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015064554713&view=1up&seq=368}}</ref> An alternative proposal, put forward in 1906 by the U.S. Navy, suggested that the [[International Code of Signals]] flag signals should be adopted for radio use, including NC, which stood for "In distress; want immediate assistance".<ref>{{cite book |first=S.S. |last=Robison |year=1906 |section=Codes |title=Manual of Wireless Telegraphy for the Use of Naval Electricians |edition=1st |page=112 |section-url=https://babel.hathitrust.org/cgi/pt?id=uc1.$b114537&view=1up&seq=118}}</ref>

[[German Empire|Germany]] was the first country to adopt the {{sc|SOS}} distress signal, which it called the ''Notzeichen'' signal, as one of three Morse code sequences included in national radio regulations which became effective on 1&nbsp;April 1905.<ref>{{cite journal |title=Regelung der Funkentelegraphie im Deutschen Reich |journal=Elektrotechnische Zeitschrift |date=27 April 1905 |pages=413–414 |url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015084596132&view=1up&seq=457}}
:
The three [[International Morse Code|International Morse]] sequences were:
: ''Ruhezeichen'' ("cease sending") {{morse|dash|dash|dash|dash|dash|dash}}, {{overline|{{sc|OO}} }};
: ''Notzeichen'' ("distress") {{morse|dot|dot|dot|dash|dash|dash|dot|dot|dot}}, {{overline|{{sc|SOS}} }}; and
: ''Suchzeichen'' ("calling") {{morse|dot|dot|dot|dash|dash|dash|dot}}, {{overline|{{sc|SOE}} }}.
</ref><ref>{{cite journal |title=German regulations for the control of spark telegraphy |journal=[[The Electrician]] |date=5 May 1905 |pages=94–95 |url=https://babel.hathitrust.org/cgi/pt?id=njp.32101050973294&view=1up&seq=118}}</ref> In 1906, the [[International Radiotelegraph Convention (1906)|first International Radiotelegraph Convention]] met in Berlin, which produced an agreement signed on 3&nbsp;November 1906 that become effective on 1&nbsp;July 1908. The convention adopted an extensive collection of Service Regulations, including Article&nbsp;XVI, which read: "Ships in distress shall use the following signal: {{morse|dot|dot|dot|dash|dash|dash|dot|dot|dot}} repeated at brief intervals".<ref>{{cite report |title=Service Regulation&nbsp;XVI |series=1906 International Wireless Telegraph Convention |publisher=U.S. Government Printing Office |page=38 |url=https://babel.hathitrust.org/cgi/pt?id=uc2.ark:/13960/t80k29264&view=1up&seq=42}}</ref>

[[File:RMS Slavonia, 10 June 1909 (Instituto de História Contemporânea).png|thumb|300px|Cunard liner {{RMS|Slavonia}} photographed the day it was wrecked on 10&nbsp;June 1909; it is the earliest-reported ship to have transmitted the {{sc|SOS}} distress call.]]

In both the 1&nbsp;April 1905 German law and the 1906 international regulations, the distress signal is specified as a continuous Morse code sequence of three dots / three dashes / three dots, with no mention of any alphabetic equivalents. However there was a convention in [[International Morse Code|International Morse]] whereby three dots comprise the letter "S", and three dashes the letter "O", and it soon became common to informally refer to the distress signal as "S&nbsp;O&nbsp;S", with the 12&nbsp;January 1907 Electrical World stating that "Vessels in distress use the special signal, SOS, repeated at short intervals."<ref>{{cite periodical |title=The International Radio-Telegraphic Convention |periodical=[[Electrical World]] |date=12 January 1907 |pages=83–84 |url=https://babel.hathitrust.org/cgi/pt?id=uva.x002212099&view=1up&seq=101}}</ref> (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&nbsp;"5", so in a few cases the distress signal was informally referred to as "S&nbsp;5&nbsp;S".)<ref>{{cite magazine |title={{nobr|'S 5 S'}} rivals {{nobr|'C Q D'}} for wireless honors |magazine=[[Popular Mechanics]] |date=February 1910 |page=156 |url=https://babel.hathitrust.org/cgi/pt?id=umn.31951002805231x&view=1up&seq=160 }}</ref>

The first ships that have been reported to have transmitted an {{sc|SOS}} distress call were the [[Cunard Line|Cunard oceanliner]] {{RMS|Slavonia}} on 10&nbsp;June 1909 while sailing the [[Azores]],<ref>{{cite magazine |title=Notable achievements of wireless |magazine=[[Modern Electrics]] |date=September 1910 |page=315 |url=https://www.worldradiohistory.com/Archive-Modern-Electrics/Modern-Electrics-1910-09.pdf#page=21}}</ref><ref>{{cite magazine |first=John |last=Edwards |date=2020-06-09 |df=dmy-all |title=''Slavonia'' sends an SOS|magazine=Oceanliners Magazine |url=https://oceanlinersmagazine.com/2020/06/09/slavonia-sends-an-sos/ |via=oceanlinersmagazine.com }}</ref> and the steamer SS&nbsp;''Arapahoe'' on 11&nbsp;August 1909 while off the [[North Carolina]] coast.<ref>{{cite book |title=SOS to the Rescue |first=Karl |last=Baarslag |year=1935 |pages=10–12}}</ref><ref>{{cite web |title=Distress signal SOS first heard at Hatteras, 1909 |website=ncdcr.gov |type=blog |date=2015-08-11 |df=dmy-all |url=https://www.ncdcr.gov/blog/2015/08/11/distress-signal-sos-first-heard-at-hatteras-1909}}</ref> The signal of the ''Arapahoe'' was received by the [[United Wireless Telegraph Company]] station at [[Hatteras, North Carolina]], and forwarded to the steamer company's offices.<ref>{{cite news |title=Notices |date=27 August 1909 |periodical=The Pacific Commercial Advertiser |url=https://chroniclingamerica.loc.gov/lccn/sn85047084/1909-08-27/ed-1/seq-4/ |access-date=20 August 2019}}</ref> However, there was some resistance among [[Marconi Company|Marconi]] operators to adopting the new signal, and as late as the April&nbsp;1912 [[Sinking of the Titanic|sinking]] of the {{RMS|Titanic}} the ship's Marconi operators intermixed {{sc|[[CQD]]}} and {{sc|SOS}} distress calls. In the interests of consistency and maritime safety, the use of CQD appears to have died out thereafter.