What's the most expensive U.S. weapons project from the WW2 era? The answer is a widely unknown piece of trivia that's good for a winning bet. It wasn't the Manhattan Project. It was the Boeing B-29 Superfortress.
The Superfortress cost an equivalent of 43 billion in today's dollars. They designed it for high-altitude strategic bombing. Only 3,970 were ever produced and It was one of the highest-tech weapon systems of its time. With a pressurized cabin and four remotely controlled gun turrets, it was capable of raining down a lot of pain from (what was back then) very high altitudes.
It was a massive machine. With four 18-cylinder propeller engines (capable of producing 2200 hp each), a 141-foot wingspan, cruising speed of 191 knots, and a max range of 5,830 miles, it could carry more than three times the payload of its predecessor, the B-17. Put another way; It would take 1,000 B-17s to carry what 300 B-29s could.
This thing is insane. The cockpit looks like the Millenium Falcon.
Keep suggestions coming. Keep them classy. No butt stuff.