Earlier quoted context omitted.
ah, neat! looks like they recently switched from 3x turboprop to 4x turbofan edit: had to correlate sources to find that a bunch of popular aviation blogs got the original design wrong. was actually 3x turbofan -> 4x turbofan
it was never a turbo prop. You'll never get a propeller driven aircraft to supersonic speeds.
https://en.wikipedia.org/wiki/Republic_XF-84H_Thunderscreech