Following the Sneak attack by the Japanese Navy the United States didn’t have the capability to mount offensive Strategic Air operations againts the Japanese mainland.
We were lucky to have the People who were willing to risk flying medium bombers off of an aircraft carrier. The planes B-24 Liberators were not designed for carrier use and didn’t have the range or the capability to return to the carrier following their mission.
The U.S. didn’t get the capability until the B-29 was brought online and then we were able to bring the whirlwind to Japan.
They used B-25's.