.....I found the following to be a very interesting review of the current and future roadmap of US bomber platforms. I used to be much more informed on things like this, but admit I'd never heard of the proposed B-21 until reading this piece.
http://www.thedrive.com/the-war-zon...etire-b-2-and-b-1-bombers-early-is-a-good-one
http://www.thedrive.com/the-war-zon...etire-b-2-and-b-1-bombers-early-is-a-good-one