The Germans knew that at some stage the Allies would launch a cross-Channel invasion, but they were unsure of exactly where or when it would take place. As a crucial part of their preparations for D-Day, the Allies developed a deception plan to draw attention away from Normandy.
The D-Day deception plan was codenamed Operation ‘Fortitude’ and was part of a larger overall deception strategy – Operation ‘Bodyguard’. ‘Fortitude’ consisted of two parts: ‘Fortitude North’ was meant to fool the Germans into thinking that the Allies would launch an attack on Norway, and ‘Fortitude South’ was designed to convince the Germans that an invasion would occur north-east of Normandy in the Pas de Calais.
Real tanks were replaced by dummy tanks when they were moved from their holding areas. The inflatable decoys made the Germans think the Allies had more tanks than they actually did and helped mask that final preparations were being made for the invasion. The deception techniques used in preparation for D-Day had previously been used in North Africa in 1941-1942 and prior to the landings in Italy in 1943.
As part of ‘Fortitude South’, the Allies created the fictitious First US Army Group (FUSAG), an imaginary force ‘based’ in south-east Britain. This also helped give the impression that the invasion force was larger than it actually was. Fake radio traffic and decoy equipment – including inflatable tanks and dummy landing craft – mimicked preparations for a large-scale invasion aimed at the Pas de Calais.
Double agents delivered false information to reinforce this deceit both before and after the Normandy landings. The most famous of these agents, Juan Pujol Garcia (‘Garbo’), invented a network of imaginary agents who were supposedly supplying him with information on Allied preparations.
Metallised strips of paper known as 'Window' caused confusion on German radar.
Allied air power also played an important part in the deception. In the months leading up to D-Day, Allied bombers attacked road and rail networks in an attempt to isolate the invasion area, but additional attacks were made on other parts of northern France to divert German attention away from Normandy.
In Operations ‘Taxable’ and ‘Glimmer’, the RAF dropped metal strips – codenamed ‘Window’ – along the French coast to confuse German radar. On the night of 5-6 June, as part of Operation ‘Titanic’, the RAF dropped dummy parachutists to simulate an airborne invasion and draw German forces away from key objectives.
The Allied deception strategy for D-Day was one of the most successful ever conceived. The Germans overestimated the strength of Allied forces in Britain, particularly in the south-east, and believed as late as July 1944 that a larger second invasion would land in the area around Calais. This helped the Allies achieve the key element of surprise and kept German reinforcements away from Normandy both on D-Day and in the weeks that followed.