Reproductions of the Top Secret “Bigot” maps used in the Normandy D-Day invasions, June 1944. (Bigot was a secrecy classification.)
According to information on the maps these were produced by the Geographical Service General Staff (GSGS), which I believe was part of the War Office (UK). Who made the maps, or where the information came from (presumably a joint US-UK effort) would be an interesting story if it’s not already told somewhere.
Related story in the NGS Magazine, June 2002.