The Allied landings on the coast of Normandy on 6 June 1944 - the long-awaited D-Day - was not only the greatest amphibious military operation of all time, it was also the decisive turning point of the Second World War. Its success opened the way for the liberation of western Europe from Nazi tyranny, and for the downfall of Hitler's criminal regime. Yet it could all have gone horribly wrong.

An opposed seaborne landing on a fortified and heavily defended hostile coastline is one of the most difficult of all military operations to pull off. Winston Churchill - with his painful memories of the slaughter following the Gallipoli landings in the First World War - was only one of several Allied leaders with grave doubts about the viability of the project.

D-Day was saved thanks to an extraordinary and wide-ranging series of deceptions that weakened and confused the Nazis. It was known overall as 'Operation Bodyguard'. Bodyguard involved the creation of phantom armies, complete with dummy aircraft, tanks and landing craft, and scores of equally bogus German spies under Allied control feeding dud imaginary information to their Nazi handlers: all aimed at convincing the enemy that the D-Day invasion would fall around Calais, or in Norway, or near Bordeaux - anywhere, in fact, but its real target in Normandy.

Operation Bodyguard was a spectacular success, one of the greatest intelligence coups in history. Evidence from German sources confirms that Hitler held back his panzers around Calais for an astonishing seven weeks after D-Day rather than the mere fortnight expected by Allied planners - believing that the landings in Normandy were a feint and that the 'real' invasion was yet to come.