This is another draft of a subject that I am interested in but for which I lack some facts or confirmation of details.
Contrary to most published articles, the second seat was added without stretching the airframe, which avoided a cg problem. Instead, equipment was relocated and two 20-mm cannon, their ammunition, and the ventral rocket pack were deleted. The aft seat was raised by 15 inches above the front seat, providing both visibility forward and replacing some of the reduction in fuselage volume. (It was also necessary to do so in order to retain the existing intake trunking that led back to the engine.) Both cockpits were covered by one long canopy that was hinged at the rear like the single-seat Crusader’s. A parabrake installation was added at the base of the vertical fin to reduce the landing distance.
In line with its intended purpose as an advanced trainer, it retained the Sidewinder missile capability and the two cannon. (The right cannons were reportedly the two removed but I can’t confirm this.)
The first flight of the prototype F8U-1T was accomplished on 6 February 1962. It was subsequently redesignated TF-8A in November in accordance with the DoD aircraft designation system consolidation.
The Navy accomplished an extensive evaluation of the TF-8A including at-sea trials.
The Twosader was also evaluated by VT-22 with student pilots. Four reportedly received training in the TF-8A. One became the first (and probably only) 1,000-mph student pilot. The Navy placed an initial order for 12 F8U-1Ts (BuNos 145648-145659) with Vought but subsequently canceled the contract because of budget priorities.
None of the other countries to which it was proposed elected to buy it either (according to Bill Spidel, France, whose Navy was operating F8Us, had some on order for a time). The one and only TF-8A was eventually assigned to the Navy Test Pilot School for several years.
At some point, it was designated NTF-8A, probably because the Navy had some TF-8As that were simply F-8As assigned to the training command. This has lead to some confusion with at least one F8U flown or modified by NASA. The NTF-8A was assigned to NASA but only briefly in 1977 after the Test Pilot school retired it. It may not have even been flown there since it was bailed to Vought in late 1977 to provide training for Philippine Air Force pilots.
It crashed on 28 July 1978 following an engine failure during a training flight from Vought’s facility at Grand Prairie, Texas. The Vought instructor and the Philippine Air Force student ejected safely. According to Bill Spidel, the "rear compressor rotor tie-rod nut cover" failed.
A Vought Public Relations multi-view drawing of the Crusader includes the F8U-1T. However, the canopy clearly appears to be a sketch and too large, both in depth and length. I’ve modified it based on photographs, etc. but can’t be sure that it is much more than better.