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

Land telegraphs had traditionally used "CQ" ("sécu", from the French word sécurité) 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.