This all started with our original comment about the photo appearing on the old WHATZITS page:

Found floating around the WWWeb some time ago, I dragged it from its dark corner to see if any Eagle-Eyes out there know what it really is. Identified only as "Republic VFX," it's a nonesuch, at least from Farmington. Likely a mock-up. "1664A" is enigmatic—buzz numbers used that "A" with duplicated numbers, but I've not seen it used in s/ns...

    This was the Fokker-Republic D-24, or at least that is the way I have always known it, but then I have always been biased towards Fokker. The D-24 Alliance was a 1965 proposal for a NATO VTOL fighter that Fokker intended to develop with Republic. There is a model of the aircraft in the Netherlands Air Museum (Schiphol). I was not aware that Republic actually built a mock-up which seems to indicate Republic was the lead partner in the Fokker-Republic deal (and I doubt Fokker had the expertise in 1965). I didn't know what the Republic model number was, but I now guess it might have been 1664A. (— Jos Heyman)

    I believe that the Republic "whatzit" might also have been known as the "Long-Range Supersonic Cruise Interceptor" as described in Joshua Stoff's The Thunder Factory(Motorbooks 1990), page 182. That text noted: "This would have been somewhat akin to the XF-103, though slower. It would have had a range of 3,000 miles at Mach 1.5, and an internal weapons carriage of multiple long-range air-to-air missiles. It was intended to defeat the atmospheric threat—high-performance, Cruise missile-launching bombers. It would feature autonomous sensing, so there would have been no dependence on AWACS nor on aerial refuelling." Sharp-looking airplane! (— Carl Stidsen)

    I'm having trouble with identifying it as a Republic-Fokker D-24 Alliance. After searching 50 years of old airplane magazines, many aircraft books, plus the Web, I came up with just one photo of a model of the above plane. This photo shows the horizontal stabilizer forward of the vertical stabilizer, which is not like your photo; also the engine intakes are forward of the wings. I know this is not much, but it leads me to believe more research is needed before this matter is closed. The photo I found is in Oct/Nov 1963 Air Progress. (— Ron Billman)

    I think these are two different projects—Fokker-Republic D-24 Alliance (for NBMR-3) and Republic VFX. I have several aviation magazines where there are images and 3-views of the D-24 model (same type as Mr Heyman's photo)

        Air Progress Oct/Nov 1963, p. 9
        Flying Review International 1964, Nov p. 11
        Air International May 1975, p. 252

Air International wrote: "It was proposed that the vectored-thrust Bristol Siddeley BS.100/3 with a thrust potential of 17500kg be used by the Alliance, with plenum chamber burning in the two forward swiveling nozzles, and it was calculated that VTO weight with 2270kg useful military load would be of the order 15,875kg while STO weight would rise to 20,400kg or more. Anticipated performance included M=1.25 capability at 150m rising to M=2.4 at altitude, with service ceiling topping 21,335m.
    The joint Fokker-Republic Project Division at Schipol was headed by Alexander Wadkowsky of Republic Aviation, but the NBMR-3 requirement proved contentious from the outset, inspiring much antagonism, both nationalistic and between competing companies, with the result that this highly ambitious and perhaps too far-sighted program drifted to its demise.
    Republic Aviation submitted a broadly similar project to that of the Alliance in the USN's VAX attack aircraft contest, but failed to find favor." I believe photo (39) is last-mentioned Navy's VAX project (or VFX competitor for F-14).
    An interesting site is with some notes about an article: "Republic TFX and Republic-Fokker D-24 Alliance." It begins: "This article describes two separate aircraft designed by Republic Aviation in the early 1960s..." A small drawing is similar to the photo. (— Kari Koski)

    I was wrong in identifying the VFX as the D-24, but at least it flushed out all the knowledge and we should all be happy about the fact we are now aware that Republic did two designs of a fairly similar concept. One problem with aviation history is that a lot of information is available in a very great many places and nobody can have access to all of them. Aerofiles allows us to seek out our combined resources and bring some of these more mysterious aircraft designs out in the open. (— Jos Heyman)