Critical to D-Day's success was Bletchley Park.
Code-breakers cracked the Enigma and Lorenz codes used by Nazi commanders, meaning disinformation to keep D-Day secret could be passed to the enemy lines and monitored.
Operation Fortitude created "ghost armies" in the north and in the south.
Military artists created fake aircraft and vehicles to divert attention from Normandy and trick Hitler's forces into expecting invasions in Norway and at Calais.
The tactic paid off, as code-breakers at Bletchley Park decoded an intercept from Japan suggesting that Norway and Calais are indeed the two locations where Hitler is expecting an attack.
Surprise Sea Invasion
The Allies secured the element of surprise. What was left to do was land the Army from the sea.
Thousands of landing craft transported men and equipment to the shores of Normandy.
Thanks to the deception game and the arrival by the sea, the Allied forces were able to land despite extensive Nazi defences.
Far from the sea and up in the skies, gliders have a critical tactical role.
Horsa gliders flew Allied forces deep behind enemy lines as silently as possible.
In preparation for D-Day, tests were carried out to ensure that tanks could be amphibious.
DD tanks – nicknames 'Donald Duck tanks' – were used by American, British and Canadian forces on 6 June 1944.
Shermans were fitted with propellers and flotation screens.
Six floating tanks never made it to D-Day, sinking and killing six crew in preparation for the Normandy landings.
In order to be able to resupply the frontline from the sea, artificial harbours known as Mulberries were created from old ships and large concrete structures were created.
Adding floating roadways and piers allowed to access the beachhead.