I Just Learned What ‘SOS’ Really Stands For, And Now I Feel Silly
But it took time to become the standard option – when the Titanic crashed in 1912, it originally used the British signal CQD, from “CQ”, meaning “seeking you” or “all stations, and “D” for “distress”. The Titanic’s crew only switched to “SOS” mid-transmission.
Article source: https://www.huffingtonpost.co.uk/entry/sos-meaning-history-explained_uk_6adf792de4b0b250be0169ea