What factors went into making d-day a success

1 Word "Technology"

source: https://answers.yahoo.com/question/index?qid=20100207111422AAe8avg

D-day had been planned for many years and so all the plans were read

False intelligence spread by the allies spread false information to the Germans.

The Germans thought the attack was going to occur farther along the coast at Calais because this was the shortest route by sea (Dover â Calais), even when the attack began on the beaches Hitler was still convinced the attack was going to occur at Calais.

B. slow down as they lose energy