CQD, transmitted in Morse code as  — · — ·    — — · —    — · ·  is one of the first distress signals adopted for radio use. It was announced on January 7, 1904, by "Circular 57" of the Marconi International Marine Communication Company, and became effective, beginning February 1, 1904 for Marconi installations.

Land telegraphs had traditionally used "CQ" ("sécu," from the French word sécurité or secours) to identify alert or precautionary 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" ("distress") to CQ in order to create its distress call. Thus, "CQD" is understood by wireless operators to mean, "All stations: distress." Contrary to popular belief, CQD does not stand for "Come Quick, Danger", "Come Quickly Distress", or "Come Quick — Drowning!"; these are backronyms.

Although used worldwide by Marconi operators, CQD was never adopted as an international standard since it could be mistaken for a general call "CQ" if the reception was poor. At the second International Radiotelegraphic Convention, held in Berlin in 1906, Germany's Notzeichen distress signal of three-dots/three-dashes/three-dots (· · · — — — · · · ) 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.)