On May 2nd 1944 one of the clues in the Daily Telegraph crossword was "One of the U.S." This gave the answer "UTAH". On May 12th an answer was "OMAHAH".
On differents days throughout May and the beginning of June The words "OVERLORD", "MULBERRY", and "NEPTUNE" were solutions to the crosswords.
M.I.5. sent two agents to Leatherhead to see Sidney Dawe, a schoolteacher who set the crosswords. When asked how 5 vital code words had cropped up in his crosswords he cold only reply that it was a coincidence. "How can I know which words are to be used as code words" Some seeds of doubt were sown as Dawe’s brother in law, with whom he shared lodgings, was a senior admiralty official.
Another explanation came to light years later.
Ron French was in Dawe’s class during the war. Dawe used to give his pupils the excercise of filling in blank crossword grids. French used words he’d heard from american soldiers in the town to fil in his grids. French had been called to the headmasters study after the visit of M.I.5 and sworn to secrecy. He kept the secret untill the death of Dawe in 1984.