Something so ludricrously expensive, the USAF/USN can only afford one, and are too afraid to deploy it in case it gets destroyed.
Every country/alliance tries to make one as well, bankrupting several smaller countries and tying up developments for decades.
It would be stealthy, hypersonic, STOVL, and semi-submersible.
You can control it with your mind, but only if you think in Russian.
Support contracts are handled by the Mafia.
And something that causes never ending squabbles online as to how bad/perfect it really is.
Alvis 3.1