The Brits were intent on producing an A-Bomb, TubeAlloys and all that, and even believed that they could have it ready by 1944/45 ... wishful thinking, of course, as they simply didn't have the resources to throw at the problems that arose that the US did ... but, of course, they did manage to build one in the end ... and the US had reneged on their agreement to share atomic technology, so the British Bomb's main advantage was that they knew it could be done and what some of the dead ends were.
That said, the US economy managed to pursue three massive resource intensive programs in WW2 ... all about the same size in terms of cost and resource expenditure ... the Manhattan Engineering District (aka the Atom Bomb), the Liberty/Victory Ship program and the B-29/B-36 program.
The Germans managed one. The V-Weapons.
The British? I suppose you call Strategic Bombing their one program, though that's a bit of a stretch.
And, of course, the US achieved all that while their standard of living actually increased during the war ... something completely unprecedented ... even allowing for rationing!
The Germans actually knew that they were overmatched by the US, especially, but also knew they couldn't match the UK or the USSR in the medium to long term ... they knew they had to beat them separately (defeat in detail) and they knew they had to do it quickly, Tooze's "Wages of Destruction" is particularly good and up to date on the details, but there are earlier books and articles that were already hinting at some of the issues as early as the 1980's and 1990's.
But, ultimately, it's like the scene at the end of Band of Brothers when the US soldiers are riding along a German autobahn in a truck and all the defeated German soldiers are marching off (home? into captivity?) on foot or on horse drawn waggons ... and one of the US soldiers yells out "What were you thinking?" at the sight and the comparison.
Hitler and the Nazis knew it was a gamble, and Hitler, at least, believed that the Aryans had to take it or die trying ... and, of course, believed that the advantage of an early rearmament, supposed democratic weaknesses, and surprise would be enough.
Author, Space Opera (FGU); RBB #1 (FASA); Road to Armageddon; Farm, Forge and Steam; Orbis Mundi; Displaced (PGD)