Every depiction of the D-Day invasion shows the infantry landing against nearly untouched fortifications. I can understand why they did not use bombers to attack the fortifications if the area was fortified with AA guns... but I don't understand why the they didn't clear a path onto the beach with heavy naval guns. Was the reason that the naval guns were too inaccurate? That seems unlikely, since in that era, destroyers routinely engaged in ship to ship battles and ships are a much more difficult target than massive concrete fortifications in front of the beach.
Maybe I am looking about this from the wrong perspective but it appears to me that the allies did not make much use of the tremendous naval firepower they had at their disposal when conducting the D-Day landings.
Oh they used naval guns alright, however, shelling another ship and trying to knock out a heavily fortified concrete coastal artillery fort are two very different things.
First of all, a coastal artillery emplacement fires back, usually with much greater accuracy than you do.
Second, a coastal artillery fort has armor a destroyer or battle ship can only dream of. Feet upon feet of reinforced concrete that is essentially impervious to all but the heaviest of guns or a one in a million hit.
Third, a coastal emplacement is a much smaller target than an enemy ship.
So these three things combine to make ship to coastal artillery emplacements very unfavourable engagements for the navy. Since the navy did not want to telegraph their intended landing spots days in advance the window for shelling the defenses was limited. The earlier you start the better your chances of clearing the defenses but you also give the enemy more time to bring in reinforcements.
What you're left with is the navy trying to, in a very limited window of time (about 40 minutes), knock out gun emplacements specifically designed to withstand naval shelling. It's not an easy task.
As for bombers, they did use them but keep in mind that the landings happened just after dawn and on a day with low cloud cover. This made bombing extremely inaccurate and many of the bomb crews dropped their cargo too far inland for fear of hitting their own troops.
In the end it comes down to the element of surprise being more important than the intact bunkers.
Not a historian exactly but a career Marine Corps officer so pretty interested in amphibious assaults. A couple of things to unpack here.
First, you can't knock out ALL fortifications with air or naval bombardment. We tried in the Pacific. A lot. You can knock out some of it but never all of it, especially if its underground. So, you have to assume you'll have to deal with it on the beach and thus prioritize tanks and combat engineers getting ashore (which the Allies did.)
Two, pilots of bombers had to fly fast because they were under fire from the ground and, because bombing was inaccurate and relatively new, pilots tended to wait an extra second or two to drop their bombs to avoid hitting friendly ground troops. The combination caused most of the aerial bombing missions directed against the beach fortifications to go long.
Third, Utah Beach was heavily fortified. Some of the other beaches were taken unopposed. The planners obviously would have preferred the unopposed beaches but that wasn't possible because...
Fourth, because Utah Beach was situated where the Cotentin Peninsula meets the mainland, landing there would isolate the German units defending Cherbourg at the tip of the peninsula. Cherbourg had to be taken because it was a port and the Allies could get more supplies ashore using a port than they could over the beaches. The Allies learned at Dieppe that taking a port directly from the sea is usually a bad idea so they outflanked Cherbourg from the south by way of Utah Beach. So even though Utah was heavily fortified, Cherbourg was an important enough objective that it had to be assaulted.