I´m just reading Anthony Bevoor´s “D-Day”.
The 15th army would have severed as a perfect obstacle in case the allied had made landing at Pas-de-Calias. But it was one with it´s equippepment, training etc. Just there, not ably to move and engage effectivly in combat in a field combat. 15th army was a 10 inf. div. army fied with their coastal artellry batteries and defense positions.
It consided of 10 infantry divisions, trained to defend this particulary area, which was military logical, not due to Operation Fortitud. This part of the coast could not being left undefended.
Instead the Germans send their reiforcements from ALL other fronts, not only weakining the already falling-apart Army Group centre in Belarussia.
Those , mostly SS (Panzer) divisions and high quality Wehrmacht divisions, made up for the most effective defense of a small territory that has become legendary in the military history.
The infantry divisions from 15th army, at most 50% where realistic to move to Normandy, since such strategic area can¿t be left without ANY defence at all!
Hence that leaves us with max. 5 infantry divisions entering the Normandy front.
They could have been deployed on the american sector, thus slowing down, uphelding Cobra, but since after they eventually where being used up, the same sitation would acure: a thin german front, without reserves. maybe max. 1 month it could had baught the germans, max, probably less! This since more troops would have triggered Hitler to order suicide-counteroffensives like that on Mortain before 1-2 times, and hence using up this reinforecements rapidly.
Eberbach, Rommel and other commanders trying to assemble panzer offensives, as they had done before on othyer theaters in Rusia, france, Africa, Italy, started several and almost everone where quickly broken up by allied naval artillery, fighter-bombers and the actual dedication to combat that allied troops showed, while defending, even it´s true that fresh troops where utterly ineffective in the allied offensive operations around Caen, Carentian and on the west wing on the american sector.
Wehrmacht defending Normandy 6th June-14 August was an incredible military achivement. A “normal” defending force of that strength in number of infantry, motorzied units, aircraft, panzer, would have fallen apart in a few weeks, if not days!
But throwing the Allies into the sea again…¡Imposible! Giving the numerous examples that when elit forces tried it. Defence, yes, almost, just almost unbreakable, but large scale-counteroffensives= ¡Imposible!
This was also calculated by the western Allies. They knew that the Red Army was going to start a huge offensive which would tie down to bulk of the already exhuasted Wehrmacht, hence 143 was to early, certain of holding a bridgehead and continuing in 1944 from that, yes. But Allied commanders and policymakes thought it, especially after Stalingrad and Kursk, that it was better that the Red Army did the bulk of the work, hence saving approx. 300,000 allied soldiers causalties and material, much of it used up insted by the Red Army, but saving Brittish and American lives ( plus all other nations involved).
When The Allied invaded France in 1944 they KNEW that would win. Luftwaffe was erradicated, Wehrmacht could NOT move daytime if hardly at all, the Red Army was soon to start Operation Bagration, pushing hard right onto Berlin!
So, as allied with Sviet at that time, 1943 would have been the best military option, insted of lurking around in remote Africa and Italy with practcally no chance of really hearting the Third Reich, just diverting some troops from the Russian front.
Head on attacks, on France, Belgium, Holland, Denmark and especially Norway costs would have cost a lot more, but also made a much more damage to the German military potenial. This if the Brittish (and Americans) had continued bombing the Ruhr area as they did march-oct 1943, when they insted turned to bombing Berlin, the most terrible mistake in the war! Adam Tooze wright that if this “Battle of The Ruhr” had continued German steel and coal production would have been reduced to such low levels that the Wehermacht would be put out of supply of steel in a couple a months or at most a year, making it hardly impossible for Germany to produce military equipment!!!
I have before thought that halting the 15th army had a great impact, but it did not. if the Allied had choosen to land at both Normandy and then at Pas-de-Calais it would had been meeting a formidable defense force, inflicting heavy cualsties among the landing allied troop, on ships, aircraft, but they where tied to their fixed costal positions and only effective there- not as reinforcements in Normandy.