For hundreds of years a national flag flown upside down was a signal for distress. A ship flying no flags might also be understood to be in distress. In the mid 1800’s various countries had different maritime regulations and the advent of steam power made it necessary to deal with discrepancies. In 1863 a new set of rules were drawn up by the British Board of Trade, in consultation with the French government. By 1864 the regulations had been adopted by more than thirty maritime countries, including Germany and the US. In 1889 the US convened the first international maritime conference in Washington DC and in 1890 the resulting Washington Conference rules were adopted and were effected in 1897. It set regulations for distress signals which included guns or explosives fired at minute intervals, rockets or flares to be colored red fired at regular intervals, orange smoke and a square flag flown with anything resembling a ball.
The Wireless Telegraph and Signal Company was formed by Guglielmo Marconi inventor of the long range radio transmitter in July 1897. In 1900 he formed the Marconi International Marine Communication Company with the purpose of providing security to life and property at sea with wireless radio apparatus. Land telegraphs had used the Morse code message “CQ” from the French “secu” from “securite” to identify alert messages of interest to all stations along a telegraph line. It was used for ships as well. The Marconi company added a “D” (“distress”) to CQ in order to create a distress call. “CQD” was used by wireless operators to mean, “All stations: distress.” It was announced in January 1904 and became effective February 1904 for Marconi installations. It does not stand for “Come Quick, Danger”, “Come Quickly Distress”, or “Come Quick — Drowning!” Between 1899–1908 9 documented rescues were made by the use of wireless.
S O S was first adopted as a distress signal by the German government in radio regulations effective April 1905 and became the worldwide standard under the second International Radiotelegraphic Convention signed on November 1906 and became effective on July 1908. It was easier to transmit 3 dots, 3 dashes, 3 dots in a continuous stream than “CQD”. It does not stand for “save our ship”, “save our souls” and “send out succour”. The first ship to transmit an SOS distress call appears to have been the Cunard liner Slavonia in June 1909. But as of 1912 there is still some resistance among the Marconi operators to the adoption of the new signal and many operators use both in emergencies.
When the RMS TITANIC struck an iceberg and sank in April 1912 another British ship, the CALIFORNIAN, was thought to be less than 10 miles away. The CALIFORNIAN had stopped because of ice and sent an iceberg warning to RMS TITANIC April 14 at 7:00pm NYT. The RMS TITANIC’s radio had been down for almost 24 hours and the on-duty wireless operator was busy working off a backlog of personal messages. When the ice warning was sent, the relative proximity made the CALIFORNIAN’s signal so loud it blew out the signals the RMS TITANIC’s operator was listening to from the wireless relay station at Cape Race, Newfoundland. The operator on the RMS TITANIC sent the message : “Shut up, shut up! I am busy; I am working Cape Race!” The CALIFORNIAN’s wireless operator listened until 11:30pm NYT turned off the wireless and went to bed. 10 minutes later the RMS TITANIC struck the iceberg. The RMS TITANIC sank at 2:20am NYT. The wireless operator on the CALIFORNIAN turned on his radio at 5:30am and found out that the RMS TITANIC had sunk overnight. If the radio on the CALIFORNIAN had been on, they quite possibly could have saved everyone on the RMS TITANIC.
On July 23, 1912 in reaction the the RMS TITANIC disaster, US president William Howard Taft signed a bill requiring ships carrying 50 or more persons to carry at least two radio operators, with one on duty at all times. It extends to not only all sea-going vessels but those travelling on the Great Lakes as well.
Text of the Radio Bill signed by Taft July 23, 1912 : http://earlyradiohistory.us/1910act.htm