"It's a CQD, old man!" CQ is what we use to hail another station ("seek you"). Hams use this all the time to call out to the ether for someone to respond. It's

"It's a CQD, old man!" CQ is what we use to hail another station ("seek you"). Hams use this all the time to call out to the ether for someone to respond. It's been used since telegraph days and early wireless was no different. BUT, the distress call before SOS was CQD. That's very difficult to hear if you're trained your brain to filter out all the other ops calling "CQ CQ CQ" all the time. Your brain will hear the incessant CQ every time you tune where other stations are sending Morse. But to hear CQD, your brain must be actively listening and making sense of what's being said - hard to hear when you're not actively listening to the incoming signals. That's one (primary?) driving reason why SOS became the de facto distress signal. It's unmistakable (... --- ...) and not a sequence heard often. It took the responding ships a moment to remember that's what was being called out over the air. "It's a CQD, old man!" was famously recorded from the account of radio operators on responding ships. ("Old man" is a friendly term for one another on the radio. In Morse, we just abbreviate as OM.)