I think this subject has already been covered in another thread but a few points all conditional by the what if factor.

1. The Naval gunfire at Normandy, Omaha in particular inadequate. It was not   because of a lack of Army experience it was because the Army Leadership chose to ignore its own doctrine FM 31-5, Landing Operations on Hostile Shores. Insufficient Naval Gunfire resources were allocated and an over-reliance on Strategic bombers (An oft repeated US failure) lead to the near disaster at Omaha beach. If the excuse for reduced Naval Gunfire was to avoid collateral damage how did they figure the use of strategic bombers would have reduced collateral damage? They were less accurate than Naval Gunfire and as it turned out dropped most of their bombs further inland than Naval Gunfire would have hit. Naval Gunfire was also more responsive than Strategic bombers.

The what if here is ha the Marines been tasked white Normandy landing can we assume that the Army and Air Corps Leadership would have listened to the Navy/Marine Corps team at all and provided not only adequate Naval Gunfire but Tactical air support?