That kind of speed takes a lot of fuel — unless it’s really a glider for most of its flight, which could make some sense, in that you’d have one less thing to conceal (i.e., not giant fireball behind you).
There just isn’t enough room for fuel for any sort of long distance travel at speed.
That said, I could see something like this getting dropped, using rocket power to get to 4700mph, then coasting over target.
It also has a drone look about it, which would also save a lot of space.
I doubt that it is Top Secret anything. But, if it were, and if I understand correctly, scram jet engines have been in development. I think they are hypersonic and very efficient.