The XB-70 was a test bed to explore supersonic flight with large aircraft, employing innovate concepts for sustaining those speeds, and controlling the aircraft during low and high speed flight regimes. We saw the low speed part when they flew the plane lazily over our town to give us a gander of that elegant plane. It was never meant for production, but tons of data would be derived from that program to apply to operational bombers. I knew the F-104 pilot who collided with the B-70. I almost drowned in his pool.