Staff Writer (Updated: 8/4/2016):
The XF-108 interested the USAF for its interception capabilities which required a very fast aircraft with a high rate-of-climb to meet the threat of incoming Soviet bombers. When the program was cancelled, North American reconstituted the aircraft's fuselage, its systems, and weapons suite into a new form to interest the United States Navy as a carrier-based, supersonic, nuclear-capable strike bomber. North American began preliminary design study work on such an aircraft as early as 1953 under a private company initiative.
While the XF-108 retained many design qualities of its bigger counterpart - the XB-70 - that made it appear cutting edge by 1950s standards, the new North American strike bomber revealed smoother lines more consistent with military aircraft emerging from the 1960s. It was a large, heavy aircraft with excellent performance for its time. The double-delta wings featured in the XF-108 gave way to a more traditional forward mainplane and rear-set horizontal tailplane arrangement with swept angles for aerodynamic efficiency at high speeds. Twin intakes were used to aspirate two engines, the pairing providing the necessary power while also increasing survivability over vast ocean spaces and enemy territory. The crew numbered two and were seated in tandem - the pilot at front with the bombardier / navigator in the rear (both positions featured ejection seats). The undercarriage was of a traditional tricycle approach and each leg wholly retractable into the body of the aircraft. A single vertical tail fin (an all-moving surface) was affixed to the extreme aft end of the fuselage and set above and between engine housings. A unique internal bomb bay delivery system (detailed below) was implemented as was an early-form of Fly-by-Wire (FBW) and Head-Up Display (HUD). At the heart of the aircraft was an advanced navigation / attack computer through the AN/ASB-12 system.
North American was handed a development contract in late August of 1956 and, a little over two years later, prototype "XA3J-1" made its maiden flight on August 31st, 1958. A second prototype was later added to the stable.
As a supersonic nuclear bomber, the aircraft featured a novel internal bomb bay release system essentially made up of a tube filling the space found between the two engine installations. This bay served a single nuclear bomb. The bomb was inserted into this bay followed by two disposable fuel tanks and all three were capped by the aircraft's tail cone assembly. When the bomb was to be released, the tail cone was jettisoned and the fuel tanks cleared the aircraft followed by the nuclear payload. In this way, the aircraft was free to deliver the armament at high speed which reduced its exposure to enemy fire and interception. An internal bomb bay also decreased overall drag as opposed to externally-held ordnance. Two external hardpoints were fitted though these became reserve stations for extra fuel stores.
After the requisite flight testing and formal evaluation phases were completed, the aircraft was accepted by the USN as the A3J-1 "Vigilante". Production models would be recognized as A3J-1A and the vehicle became the first (and only) Mach 2-capable attack bomber to serve the branch. The first squadron to equip with the type was VAH-3 during June of 1961 and the aircraft was used to succeed the aging Douglas A-3 "Skywarrior" line in the carrier-based strike role. During 1962, the U.S. military adopted an all new naming scheme for its aircraft which revised the A3J-1 designation to become "A-5". As such, the early A3J-1A models became "A-5A".