I honestly believe if a B2 Spirit flew back in World War I, the people will think it’s a dangerous alien spacecraft only to find out it’s built by their own grandchildren.
The best part is that the Nazis already had blended-wing designs very similar to the B-2 in late WWII. The Horten H IX a.k.a. Horten 229 jet fighter had its maiden flight in 1944, and an order was actually placed. I guess that if the Messerschmitt Me 262 was a nuisance to Allied fighter pilots, the Horten 229 may have become a nightmare. The almost complete mid-section of the V3 prototype which never flew still exists in the USA today, undergoing restoration (you may wish they rebuild the missing wings in a time when it’s possible to build an entire Me 262 from scratch that actually flies) but open to the public. And there’s a full-scale dummy model of the very same bird on display in San Diego.
And then there was (or rather, could have been) the Horten H XVIII, a jet-powered Amerikabomber concept that was scheduled to be built by 1946. It should have had a range of up to 6,000km and thereby been able to bomb the US mainland. It would have had to land on a US airfield afterwards because the range wouldn’t have been sufficient to return to Germany from the bombing raid, but before WWII ended, there actually weren’t any bombers capable of flying the distance between the Reich and the USA with a full bomb payload and without refuelling, so that would have been an enormous technological advantage.
Now, shortly after the end of WWII, Boeing pulled out the B-52 that could fly from the US mainland not only to the edges of Germany but way into the Soviet Union with a heavy payload, drop the payload and fly back again without refuelling.
Nonetheless, the Nazis had blended-wing jets before the USA had blended-wing prop planes.