 Additionally, the engines were changed to the R-4360, which produced higher power, had better cooling, and were less prone to failure.In 1947, with the advent of the USAF, the B-29 was redesignated as a medium bomber.With the new heavy bombers in production Convair B-36 Peacemaker and Northrop YB-49 and the planned production of both the Boeing B-47 Stratojet and the Boeing B-52 Stratofortress becoming a reality, the Superfortress was quickly becoming eclipsed by technology.