Why didnt the Allies use air superiority to wipe out the Nazi's beach fortifications before Normandy invasion?

Answer 1

A variety of reasons. The fortifications were well built difficult to destroy. They were protected by anti-aircraft weapons. Air superiority was not yet absolute. The number of aircraft and bombs required would have been enormous as they were no where near as accurate as today. Most importantly it would have told the Nazi's where we intended to attack and they would have re-enforced the area making a successful beachead impossible.

Answer 2

The beach fortifications were mainly built on sand which absorbs explosive force so would have been difficult to destroy by bombing.unless it was very accurate.
The other problem was that the Normandy beaches are quite level and firm thus allowing heavy equipment to be landed.
If they had been heavily bombed they would have been a mass of large craters and sand hills making forward progress impossible.
Also it would have eliminated the element of surprise which was essential for success

Answer 3

They did try to use bombers & naval guns to suppress & destroy the defensive positions but unfortunately, many of the shots fell further inland rather than directly onto the fortifications.