The US produced somewhat north of 300,000 aircraft of all types (!), including some 10s of 1000s of the most popular of the bomber designs. The B-24 had a lower flight ceiling than the B-17, making them more vulnerable to ground fire.
Most of the earlier B-number planes built for WWII were scrapped by 1950, although (it sez here) an iteration or descendant of the B-24 was used in Korea.
Iwo Jima was taken to provide an emergency landing site for ailing B-29s, which were the long range bombers used to drop conventional incendiary bombs to incinerate 45 Japanese cities by August ‘45. While the battle of Iwo Jima was in progress (but the four airfields had been brought under US control) the first of such planes landed for repair. Every little flyspeck of land took on great importance in the Pacific War.
Even the B-29 was produced in the 1000s, and some of the largest B-29 raids on Japan’s home islands involved 1000 planes at a time. They must have had coordinated takeoffs from multiple bases with different flight times so they’d arrive together.
Four airfields s/b three airfields, I think, but I’m too lazy to look it up.