MI5 Agent Hugh Astor recalled:
The deception plan for Overlord was brilliantly thought out. The mastermind really, was Davis Strangeways. The cover plan created an imaginary Army and we created the impression we had almost twice the number of troops than in fact were in existence.
It was quite interesting at the end of the war when we went through all their files and found that they had recorded with details all these imaginary units, the names of commanding officers, their divisional signs and all the rest of it. The effect was that, up to a point we were able to persuade them that the Normandy landings, when they started, were a diversionary attack and that the main force was still in East Anglia waiting to go across the channel to Calais.
“... you can give away an awful lot of real information to make the deception look credible .”
We were fortunate that senior people, starting with the Prime Minister and Montgomery, believed wholeheartedly in deception and were willing to pay a price to make the deception credible. When you come to think of it you can give away an awful lot of real information to make the deception look credible - all without actually giving away your plans or helping the enemy. You can say who the commander of such and such a unit is, you can give his name, address and all the rest of it, but it is not until that unit is in an assault position that the information becomes delicate.
To have a deception plan you’ve got to know the real plan. Well, nobody knew the real plan except for a very small number of people. Some would know the place, others would know the date, others would know the composition of the invading force, but very few people knew the whole story.
Those that did know it were codenamed ‘Bigoted’: it meant that they had access to all the information. My colleagues and I, who were carrying out the deception plans had to be Bigoted. We had to know the full story in order to give the deception plan.