I know, should have elaberated more.But the USA had nothing to do with the cracking of Enigma (don't believe Hollywood), so that wouldn't have been affected by the USA being neutral.
The british had the advantage of superior intelligence over Germany. Most German agents were identified before the outbreak of the war, although they some in ways were able to slip through detection, only to be caught later on.
SIS had hundreds of Agents in Germany, and were laying lies and false info for the German forces and its leaders, about Britains situation and its force numbers as well as morale. The german Abwehrs incompetance was too good to be true, and it was not until the Engima was cracked by Dilly Knox, Chief Cryptographer at Bletchly Park Cypher HQ. At First SIS thought they were being played, but Abwehr really were that stupid and incompetant that no matter what their agents said, it was lapped up, and their agents were easily turned double in no time. -see, no USA help in screwing over old jerry.
Britain had something the US didn't, Intelligence and it was this that helped all sides, especially D-Day.
The US could not have done anything if invading without being slaughtered and the British could do little in invading without US. The Role of both led to the Downfall of Hitlers Nazi Germany, each was as vital as the other, no matter what is said, US would have been pushing shit up hill with the British, and the Brits would have been riding it to nowhere without the US.
Poland too, Polish pilots flew for the RAF in Battle of Britain as well as Commonwealth nations. I think ANZAC pilots had the most Aces over everyone else...woot!Firstly, the UK never faced Fortress Europe alone. There were also India (which could have contributed more, if the British governments attitude had been different), Canada, Australia, New Zealand, South Africa, several West Indian territories, much of Africa . . . plus countries which weren't colonies or dominions but tied in by British economic interests. The contribution of that lot was immense, both in manpower & materials.
As said, if Hitler had of kept going for the Airfields, nothing would have stopped a German Invasion, as Goering had this task before any land forces moved, and they were in France preparing. But RAF launched a daring raid on Berlin, which enraged hitler to order the desruction of British Cities, leading to the sacrafice of Civilians for the rest of the Nation, not a great outcome, but they died for their country.