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Some people are probably going to argue and say "The B29 was designed to be unescorted or high altitude" It was for both. Its range was longer than any fighter of the time, if the purpose was to take advantage of that range, then no fighters could have escorted it the whole way. If you claim the purpose wasn't to be high altitude, then you're just wrong.
The initial B-29 concept and design studies were for a high altitude bomber that could do its job from high altitude - and from medium and low altitude.
The B-17, B-24, B-29, B-32 all had ranges far beyond the range of any fighter aircraft that saw service before the very end of the war. When their programs were started they were all intended to be able to do their job unescorted if necessary.
Remember the initial B-29 concept and design stages took place before any USAAF long-range heavy bomber missions had been flown.
At the start of its program in 1936(?), the B-17 design(with turbosuperchargers) was as fast or faster at 30,000 ft than any(?) fighter/intercepter in service.
At the start of its program in 1940(?), the B-29 design(with turbosuperchargers) was as fast or faster at 35,000 ft than any(?) fighter/intercepter in service.
The B-17 (and B-24 as the B-17's alternate by default) were advertised as 'flying fortresses', able to defend themselves against the enemy fighters and still get through to the target.
As it turned out, none of the above mentioned bombers were able to defend themselves against enemy fighters, and none of them could be escorted all the way to their maximum ranges by any fighters that saw service during the war. The P-82 maybe came the closest to the needed max escort range of any of the war-time escort fighter designs/programs.
Therefore, if the B-29 was a failure, all of the US heavy bombers were failures?