This Day in American Military History

21 September 1942: The Boeing B-29 Superfortress made its debut flight. The B-29 was a four-engine heavy bomber, carrying loads almost equal to its own weight at altitudes of 30,000 to 40,000 feet. Innovations included a rear pilot console and a radar bombing system. The B-29 would see significant action during World War II.

Brandus, Paul. This Day in U.S. Military History (p. 229). Bernan Press. Kindle Edition.