Only about 1500 B-29s were made during the war, not counting those kept state-side for training and preparation/testing/ramp-up.
About another 1000 or so were made after the war. The B-29 was actually rather short-lived, compared to the planes it replaced.
B-292,513 produced (total)
1,620 produced by Boeing (Wichita plant)
536 produced by Martin (Omaha plant)
357 produced by Bell (Marietta plant)
B-29A1,119 produced (total) by Boeing (Renton plant)
B-29B311 produced (total) by Bell (Marietta plant)
3,943 B-29s (B-29s, B-29A, B-29B) were built during World War II.
The B-29C production was cancelled due to the war's end, none were built.
200 B-29Ds were ordered a month before the war ended in the Pacific but reduced to only 50 after VJ-Day. The B-29D was redesignated as the B-50 as a ruse to keep production going by claiming the engine upgrades to the B-29D was so much that it ended up being an entirely new plane.
The B-50 (B-29D) stayed in USAF service until 1953 in the bomber role (phased out when the B-48 was introduced) while still serving in the USAF up to 1967 in the tanker and weather recce role.
As you can see, the B-29 enjoyed quite a long life in the USAF and more than 1,500 B-29s of all types built during the war.
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