SOS Accepted as Universal Distress Signal (1908): For centuries, ships became isolated as soon as they left visual range of shore and of other ships. This meant that if a ship encountered any problems while at sea, they could sink without anyone knowing their fate. This isolation ended with the invention of the wireless telegraph and Morse Code.
By 1904, many transatlantic ships had wireless telegraph capability on board. Realizing a need for a widely recognized distress call, the letters "CQD" became the first distress call. At the time, both on land and at sea, the letters "CQ" preceded any general message meant for all stations. Thus "CQD" means "All stations, distress" and not "Come Quick Danger."
At the Radiotelegraphic Conference held in Berlin in 1906, it was noted that there needed to be an internationally agreed upon and recognized signal for distress. No longer should Great Britain use "CQD" while Germany used "SOE." A single distress call was needed.
After much discussion, the letters "SOS" was agreed upon. Although many have later stated that the letters stand for "Save Our Ship," "Save Our Souls," "Sink or Swim," or "Send Out Succor," this is not true. The letters were chosen for the ease and unmistakability of three dots, three dashes, and three dots and not for the actual letters of "SOS."
After being agreed upon at the 1906 conference, the Morse code signal of three dots, three dashes, and then three dots (sent together, without spacing) went into effect as the international signal for distress on July 1, 1908.
Although now officially the international signal for distress, many people still used the old signal of "CQD." Even in 1912, when the Titanic began to sink, its radio operator placed the "CQD" distress signal until another operator suggested to also send the new "SOS" signal. It took several years for "SOS" to replace the old signal.