According to the new discovered documents, D-Day code was changed last minute in the weeks before the invasion over the fear that Adolf Hitler had cracked it.
The Allied high command had used the codename Overlord for the invasion on June 6, 1944, since it was conceived in 1943, the Daily Express reported.
But secret documents unearthed among the possessions of a late Army officer involved in the planning of D-Day show commanders changed it at the last minute.
An urgent memo said Overlord should become Hornpipe, while D-Day should be referred to as Halcyon. A 24-hour delay would be known as Ripcord.
Fears on the original codenames were raised when they appeared in a newspaper crossword.
Richard Wheeler, from Durham, stumbled on the papers when he was clearing out the home of his late father, Major Sam Wheeler.
The papers will appear on the Antiques Roadshow.