No right answers so far, but all this participation earns a hint, at least. So: One of the clues so far, though absolutely accurate, seems to have led everyone astray. Not that I ever intended any such thing.
Looking for the name of a warbird.
1. Never used in the role for which it was designed because the service it was designed for chose a less-expensive and perhaps better aircraft.
2. But a few were ordered for a different use.
3. Four engines.
4. Not many built: something in the neighborhood of 20. But it served for approximately ten years.
5. Armed with cannons and machine guns, and could carry bombs. Whether it ever did carry bombs I don't know.
6. A couple of them were shot down.