Originally conceived as a supersonic long-range strategic nuclear heavy bomber, the B-1 has evolved into a very effective multi-role conventional warplane.
Initially a Mach 2.2 design in the B-1A, and subsequently cancelled, the bomber was reimagined and resurrected as the Mach 1.25 B-1B with improved low-level penetration capabilities. Soviet air defenses continued to improve, and high-altitude aircraft were at risk, as proven by the earlier U-2 incident. Consequently the USAF shifted strategy to high subsonic speed low-level penetration attacks.With the fall of the Soviet Union the nuclear role of the B-1 was soon ended, leading to the aircraft being converted for conventional roles, which the heavy bomber has become very adept at.

The Evolution of the B-1 and its Adaptation to Modern Warfare
Originally conceived as a supersonic long-range strategic nuclear heavy bomber, the B-1 has evolved into a very effective multi-role conventional

A B-1B Lancer of the 9th Expeditionary Bomb Squadron taking to the skies on Oct. 19, 2021, at RAF (Royal Air Force) Fairford, United Kingdom. An impressive sight anytime but dramatically amplified in this image taken during low light conditions. (Image credit: United States Air Force/Senior Airman Colin Hollowell)