By December 1951 the Air Force had already turned its attention to a further improved version, the F-102B. Initially the main planned change was the replacement of the A-model's Pratt & Whitney J57 (itself replacing the original J40) with the more powerful Bristol Olympus, produced under license as the Wright J67. By the time this would be available, the MX-1179 was expected to be available, and was selected as well. The result would be the "ultimate interceptor" the Air Force wanted originally. However, while initial work on the Olympus appeared to go well, by August 1953 Wright was already a full year behind schedule in development. Continued development did not resolve problems with the engine, and in early 1955 the Air Force approved the switch to the Pratt & Whitney J75.