To follow up on Conslaws comments...
The B-29 was the costliest, US weapons system in WWII. I would argue that the bomber was rarely used as designed until Korea. The first few high-level bombing raids yielded terrible results. Japan had a fairly consistent, what we now call, jet stream. It dissipated the bombs dropped from above 30,000 and the bombsights could not account for it. Thus no effective bombing campaign could be conducted at over 30,000 feet.
When LeMay replaced Hansel he quickly realized this and switched from bombing factories and facilities to terror bombing, eventually killing over a million civilians. The Japanese were defenseless against these firebomb attacks. Many were flown at 7,000 ft.
Most of the B-29 were flying below 10,000 feet. The very expensive pressurized system was not used. The very expensive remote-controlled fire-control system not used either as LeMay had them removed to increase the bomb load. The way the Super Fortress was used, made a farce of all it's innovations and it was incredibly costly.
I want to make it clear that I am not denigrating the incredible feat of creating and building these aircraft. Circumstances just negated many of the incredible advances when the bomber was used over Japan.
Interesting to note, my research for the World War Three 1946 book series, has led me to believe that Moscow and the area of the Soviet Secret Cities and manufacturing centers in the Urals also had long periods of a strong jet stream that would have been a challenge in any conventional bombing campaign.