CQD, transmitted in Morse code as - · - · - - · - - · · is believed to be the first distress signal adopted for radio use. It was announced on January 7, 1904, by "Circular 57" of the Marconi International Marine Communication Company, and became effective, for Marconi installations, beginning February 1, 1904.
Land telegraphs had traditionally used "CQ" to identify messages of interest to all stations along a telegraph line, and CQ had also been adopted as a "general call" for maritime radio use. However, in landline usage there was no general emergency signal, so the Marconi company added a "D" to CQ in order to create its distress call. Contrary to popular belief, CQD does not stand for "Come Quick, Danger", "Come Quick - Drowning!" or "Come Quick, Dammit!"; these are backronyms.
Although used worldwide by Marconi operators, CQD was never adopted as an international standard. At the second International Radiotelegraphic Convention, held in Berlin in 1906, Germany's Notzeichen distress signal of three-dits/three-dahs/three-dits (· · · - - - · · · ) was adopted as the international Morse code distress signal. (This distress signal soon became known as "SOS". Germany had first adopted this distress signal in regulations effective April 1, 1905.)
In the early morning of January 23, 1909, whilst sailing into New York from Liverpool, RMS Republic collided with the Italian liner SS Florida in fog off the island of Nantucket, Massachusetts, United States. This was the first occasion on which the CQD distress call had been sent by wireless transmission.
During the sinking of RMS Titanic in 1912, its radio operator Jack Phillips initially sent "CQD", still commonly used by British ships. Harold Bride, the junior radio operator, then suggested the new code "SOS" be used, and Phillips began to alternate.