"While some members of MI5, Britain’s counter-espionage service were whiling away their spare moments in May 1944 by doing the Telegraph Crossword, they noticed that vital code-names that had been adopted to hide the mightiest sea-borne assault of all time appeared in the crossword." https://www.historic-uk.com/HistoryUK/HistoryofBritain/Crossword-Panic-of-1944/