There are probably no lessons to learn. The ETO has experience of Torch Husky Avalanche, Shingle already but the overall situation is totally different.
All the Invasions in the Pacific to date are against isolated garrisons, with limited supply and no hope of resupply or reinforcement unless the IJN sallies forth and Defeats the USN, Which they can try maybe twice before there is no IJN.
In Normandy the prospect is of about 7 Panzer Divisions being available immediately, Around 1,000 aircraft in Luftflotte 3 and the potential for that to be reinforced from central reserves or anywhere else in Europe on a few days notice far faster than seaborne reinforcement could arrive and be supplied. And you are a couple of days sail from the entire U boat arm so telegraphing the invasion is just not on, and invasion prep of the style used in the Pacific not feasible. So the allied forces have to interdict reinforcement fly cap and do a massive ASW and anti Mining operation throughout.
Overall the problem is not how do we storm the beaches but how do we stop a counterattack in the next day or so from a couple of Panzer armies.
fire control party would grid out where to put a few dozen shells over the course of two or three hours careful shooting per day
And generally miss. It is really hard to hit a target, even if you can identify it with predicted fire, comparatively easy with observed fire but that's a lengthy process with no certainty as to whether you have been successful until the position does not open fire later on. This is a lesson of WW1 that the US never learned. The immediate bombardment will not destroy even lightly hardened positions and if you are attacking without armour an MG will stop you dead until it is suppressed. What you can do is suppress the enemy for the length of the bombardment + maybe 2 minutes.
The beaching at UTAH was a cakewalk. If the British had tried OMAHA, even with Hobart's Funnies they would have been cut to pieces just like the Americans were. So, let us put that myth to bed.
See also JUNO which is very well documented. The Canadians there do a very different assault from OMAHA with a lot of direct fire support so its not just the funnies - though that would make a vast difference its also the light craft inshore from the start. Omaha is harder to be sure but a lot of the German positions remain intact until they run out of ammo on Juno there was a method in place to destroy them, whether it would have worked is another matter but the US did not even try.
I tend to think the mistakes in OVERLORD can be liberally spread around, but the British were less experienced and successful than the Americans
Jubilee. Torch Husky Avalanche, Baytown, Slapstick, Shingle, These are the experience of landing against significant forces. From the Pacific at this date, Tarawa? Most of the rest are much smaller scale and generally against very limited opposition.
LVTs at OMAHA? I've read that case made. OMAHA could have been bum rushed,
One also wonders where the LVT will come from and how they will get past the obstacles much less up the bluffs. OMAHA is actually a bad place unless you have direct fire available when the unsuppressed MGs open up. Whether thats from tanks or warships does not matter that much.
More than anything else about NEPTUNE, I have gripes about the wrong lessons learned as to air support
Disagree. There are too many variables in air support from the Heavies to make it precise. Everyone is working off different clocks with too many unknowns and the bombers will be taking off and forming over a long period before they are needed. The bombing parallel to the beach idea, Well who? the extreme flank of the formation, with everyone else bombing inland, or is it a line of bombers in column bombing over half an hour or more into increasingly obscured ground on the off chance a bomb will penetrate a reinforced bunker? with the invasion force circling around in range of an unknown number of guns shelling them and the unarmoured LST.
Most of the tactical aircraft who might be useable in a more precise way have to be used for CAP and in any case would conflict with any NGF.
f. Ehhh. I'm not sure even US Marines could have cleared CAEN as scheduled. It was a tough objective with horrible ground to traverse. Now Falaise Pocket? Marines would have closed that sack. And screw the boundary question.
So hows the Marines going to fare against 12th SS and 21st Panzer who are both in action late on 6th June. And this is the basic problem with talking about CAEN or the marines with very limited armour and artillery support going up against the single largest concentration of german armour ever assembled. Look at the frontage. They guys maybe but its not going to look at all like a WW2 Marine division.
The basic problems with the movement towards CAEN is while the Air forces want it for the airfields on day 1 so its in the plan its never really feasible. To pass through with enough force on a narrow front against first one KG of 21st panzer, then the rest then 12th SS over a fortress - HILLMAN with armoured cupolas capable of defeating direct hits from a 17lb. defended by a regiment is never going to be a walkover.