The Air Force authorized the fitting of a Westinghouse J40 turbojet in the first few examples of the F-102, but later production aircraft were to have the appreciably more-powerful Wright J67 (a license-built version of the Bristol Olympus). The J40-powered F-102 was to be capable of a speed of Mach 1.88 at 56,500 feet, with the J67 production version capable of Mach 1.93 at 62,000 feet.
By December of 1951, it was apparent that the Wright J67 engine and the MA-1 fire-control system would not be ready in time. This forced the USAF to change its plans. At that time, the Air Force decided to proceed with an interim version of its 1954 Interceptor, one which could be introduced into service at an early date, pending the availability of the fully-developed version at a later time. The interim version was to be designated F-102A, with the fully-developed advanced version being designated F-102B. The F-102A was to be powered by the less-powerful Pratt & Whitney J57 turbojet, but the F-102B was to retain the high-thrust J67. The F-102A would be equipped with an interim fire-control system, but the F-102B would be equipped from the outset with the highly-sophisticated fire control system being developed by Hughes under project MX-1179.
Although the F-102A was considered only as an interim version pending the availability of the F-102B, the F-102A ran into some unexpected developmental difficulties and fell behind schedule. A lot of money that had originally been planned for the F-102B now had to be diverted into fixing the F-102A's problems. Consequently, the F-102B fell even further behind schedule and began to lose some of its original high priority.
By mid-1953, the MX-1179 fire control system (later to be known as the MA-1) was slipping badly, and it took another year before an experimental installation could be installed aboard a T-29B for testing. At the same time, the Wright J67 engine was experiencing difficulties of its own. The Air Force had to consider alternative powerplants, and finally settled on the Pratt & Whitney J75, which was an advanced version of the J57 which was used in the F-102A. The substitution of the J75 engine for the J67 was approved in early 1955.
Seventeen F-102Bs were ordered in November of 1955. Their serials were 56-451/467. The F-102B mockup was ready for inspection in December of 1955. On April 18, 1956, the Air Force finalized the F-102B production contract of the previous November, earmarking all of the 17 aircraft ordered exclusively for testing. One prototype was to be delivered in December of 1956, with the others to follow in January of 1957.
On June 17, 1956, the designation of the F-102B was changed to F-106A. This redesignation was a recognition of the past technical differences that had distorted the original F-102 program and also a recognition that the F-102B was by now a completely different aircraft from the F-102A and was far more advanced.