[hga]

Well, the B-52 has in fact reverted to limited role, I gather for delivering nukes it's limited to delivering stand off missiles outside the range of SAMs etc.

The fly really high concept, going back to e.g. the WWII B-25 Superfortress, ended, and the B-1 went in the direction of low level penetration (below radar, and hard to pick up from ground clutter by fighters above it, something the B-52 tried for a while, but it wasn't designed for that), and the B-2 back to flying (fairly) high, but essentially invisible to radar (it can be detected in a general sense by certain types of radar, but not such that you can shoot it down).

We had to transition from piston engines if for no other reason than reliability and maintenance, plus, commonality and safety in fuel, etc. etc. The B-37 was our last in the strategic bomber role, also see the piston powered CAS A-1 (https://en.wikipedia.org/wiki/Douglas_A-1_Skyraider), heavily used in Vietnam, which the A-10 replaced.