At first, the USAF thought the conversion would be an easy matter of removing the carrier-specific features, so no prototypes were ordered, just five pre-production RB-66A models (the reconnaissance mission being considered a higher priority). The list of modifications grew, and before long, the supposedly "easy" conversion became what was a substantially new aircraft. Many of the changes were due to the Air Force's requirement for low-level operations, while the Navy version was originally designed and initially employed as a high-altitude nuclear strike bomber. Two major differences between the A-3 and the B-66 were in terms of powerplants and emergency crew egress systems. In terms of engines, the A-3 had two J57 turbojet engines, while the B-66 had two Allison J71s. Secondly, the B-66 was equipped with ejection seats while the A-3 was not.
The first RB-66A pre-production aircraft flew in 1954, while the first production RB-66B aircraft flew in early 1955.
The basic B-66 "Destroyer" design proved itself to be a versatile one, and was produced or modified into a variety of versions, including the EB-66, RB-66, and the WB-66. Likewise, the A-3 Skywarrior was used as the A-3, EA-3, KA-3, EKA-3, TA-3, RA-3, ERA-3 and the UA-3.
