What happens if, after the conclusion of operations in N. Africa and the invasion of Sicily, in 1943, the German high command rates Montgomery as the most dangerous western allied commander, and this becomes known to the planners for D Day in the UK?
For the sake of deception, do Patton and Montgomery get swapped over in roles, with Montgomery being kept back in charge of the decoy army, in southeastern England (which is supposedly going to cross the straits to attack Calais), whilst Patton has control of the forces in Normandy?