For months before D-Day on 6 June 1944, elaborate false signals and deployment of decoy forces had tried to lead the Germans to expect an invasion not in Normandy, but across the Channel at the shortest point from Kent, or even in Norway.
The ploy was more successful than the Allies could have dared to hope for, and when invasion came the Germans did not realise they had been fooled, but continued to wait for a wider attack.
The Allies had broken the German 'Enigma' code and were able to decipher enemy messages, giving the invasion force an invaluable advantage. An intercepted communication read: 'According Gruppe West at 1500 hours 6th: Allied landing Deauville-St Vaast now in progress recognisable as a major operation. The proclamation by the Allied leaders and the disposition of allied forces pointed to further major operations, but no details available regarding their targets. All to be prepared for surprise attacks.'
On the evening of D-Day a message timed at 6.55pm gave a strong hint of the German strategic confusion over what to expect next: 'North of Seine quiet so far. No landings from sea. Pas de Calais sector: nothing to report.'
Most tellingly, a document reached the Prime Minister, Winston Churchill, on 8 June, showing that the Channel reconnaissance orders to German forces for the night of 7-8 June had been: 'Further enemy landings are to be expected in the entire coastal area.' Churchill noted the paragraph in the margin.
The extent of the Germans' confusion continues in the same message: 'Enemy landings for a thrust toward Belgium to be expected.'
The German uncertainty is shown by an intercepted message on the eve of D-Day, when the forces had already set sail, ordering a full alert to the east of the Normandy invasion beaches.
Early on 6 June, commandants from the Pas de Calais and all around the coast were ordered to rearward positions on the expectation of an invasion in their area.
Signals picked up by the British show a scattered picture building up as the invasion grew, and its significance was realised.
The earliest signal of a German response to D-Day comes in a 3.30am report by a German ground attack unit moving to Laval, between Rennes and Alencon. Three more intercepted documents early on 6 June, report landings on the west coast of Cherbourg peninsula.
The first is recorded at 4am. A message from 709 Infantry Division reports landings from Quineville as far as Marcouf.
A message from a German commandant in Normandy at 6.30am reports: 'Enemy tanks land between Vire and Orne. Coast near Pont du Hoe ascended with scaling ladders.'
By 7.35am, the Germans were claiming to have destroyed 35 Allied tanks and 600 paratroopers landing near Turqueville.
Another message reads: 'West coast of Cherbourg peninsula. 1000 hrs. Further disembarkations between 1km and 10km to eastwards. Tanks and infantry against Asnelles. Arromanches under fire. Longes still under fire.
Further messages between German commanders report: '1030 radar station at Arromanches under fire from ships' guns and surrounded by tanks and infantry.' '1500: large shipping formation, also landing craft, stationary, northeast to east of Barfleur.'
And later: 'Hundreds of gliders reported over the north coast of the Cotentin. First wave landed near St Vaast at 1855; second wave, over 100, landed 1905.'