The F15 is the F15EX variant, a brand new version of the old F15, which first went into production in 1976. The planes history dates back to tests that go as far back as 1972.
The enormous Mig 31 first went into production in 1981 and has a history that goes back to 1975.
Why are they back?
Missiles.
The F15EX can carry a seven foot long missiles that can reach deep into China, should the need arise, and its external hard points can carry more missiles than the F35.
The Mig 31, which might simply be getting an overhaul rather than new editions, can carry missiles that can reach into low orbit and hit satellites.
And so the Cold War sort of returns, in a way.
