Gen. Dwight D. Eisenhower speaks to U.S. Army paratroopers on June 5, 1944, one day before the successful D-Day invasion against Axis forces. (U.S. National Archives via Reuters)

In the month leading up to the Allied invasion of Normandy in World War II, a collection of very particular words started appearing in the crossword section of a popular British newspaper.

Starting around May 2, 1944, code words for specific parts of the “D-Day” operation — which would kick off in earnest June 6 — began popping up as answers in the Daily Telegraph’s crosswords. The strange coincidence, deemed by some the Crossword Panic of 1944, led British intelligence to question the puzzles’ creator.

According to an article from the Telegraph in 2014 and a British online history magazine, the answers included the code names of the beaches where Allied forces would eventually go ashore, including the U.S. sectors code-named Utah and Omaha, and other parts of the invasion. One puzzle included the answer “Mulberry,” likely after the artificial harbors that were to be anchored off the coast of France to help move equipment to the beaches. On May 27, another question’s solution was the code name for the entire invasion: overlord.

It is unclear which puzzle caused investigators to track down who was writing them, but according to Historic UK, two officers were sent to Surrey, England, in May or early June to question Leonard Dawe. Dawe, 54, was headmaster of the Strand boys’ school. He denied any intent to disclose classified information and was never charged. MI5 chalked it up to coincidence. In an appended note to the article in Historic UK, however, a former student at Strand offered a potential explanation for Dawe’s inclusion of the codewords.

“Mr. Dawe was a compiler of puzzles for the Daily Telegraph and it was often his practice to call in 6th formers and ask them for words for inclusion,” Richard S. Wallington wrote to the British site. “At that time, the U.S. Forces were liberally strewn through Surrey, particularly in the Epsom area, and there is no doubt that boys heard these code words being bandied about and innocently passed them on.”

Operation Overlord, or D-Day, as it has come to be known, was one of the pivotal moments of World War II and was covered in a shroud of secrecy to maximize the element of surprise. More than 100,000 Allied troops jumped from planes, landed in gliders and trudged ashore from landing craft onto the fields and beaches of northern France. They faced heavy German resistance and had to contend with thick hedgerows that impeded their advance and provided a natural bunker system for German troops. By the end of July 1944, more than 300,000 from both sides had been wounded or killed.