The actual invasion of Normandy, just in terms of ships, involved 1,213 warships, 4,126 transport vessels and about 1,600 vessels of other types.
The US produced 2,710 Liberty ships and 534 Victory ships to transport this stuff to the ETO and PTO.
In addition, the US produced 35,000 landing craft to get the troops ashore.
Let's also not forget we produced 24 Essex class aircraft carriers along with 101 escort type carriers. And we were slowing production down of these in late '44/early '45.
The key stat though was oil production. We were self sufficient and Germany wasn't.
Simply put, Germany did not have the industrial base to produce anything near this requirement to deploy a force across the Atlantic and to sustain it.
The US was the only country with the industrial base to be able to conduct a two front strategy while supplying its two major allies with substantial military aid.
“Simply put, Germany did not have the industrial base to produce anything near this requirement to deploy a force across the Atlantic and to sustain it.”
...which is why they were so interested in lightning war. Had they consolidated their gains, the territories that they took had those resources.
“This required a massive production of Liberty ships along with escort carriers and destroyers to secure the Atlantic. “
Well, as Stalin supposedly said, “Quantity has a quality all of its own”.
Ship and oil production - crucial factors you note.