Please don't be too frustrated, MJD. For you to be completely frustrated should take several more clues. But here's another clue to aid the process. Thanks; Ernie P.
Question: What warbird do I describe?
Clues:
(1) There were only two prototypes constructed; but its influence was perhaps profound.
(2) It was a single seat, single engine, low wing monoplane of all metal construction.
(3) It was equipped with a tailwheel and retractible main landing gear.
(4) It was a promising design, but by the time it was ready for production, other perhaps more capable aircraft were already in production. So, this one was abandoned by the powers that be.
(5) To some it was an unneeded design. But others may well have seen it as a pattern.
(6) It was intended to meet a specific design for use in a certain area; but eventually it was decided to leave both the design and the use unfilled. This was perhaps due to more pressing concerns.
(7) The designs which ultimately obseleted this aircraft were based on other, newer engines with much more power and development potential.