With the ending of B-2 Spirit production in the early 1990s, the U.S. Air Force was left with a gap in its bomber development. A new bomber would be needed in the 2037 time frame to replace retiring B-52s and B-1 Lancers according to the Air Force's Bomber Roadmap, released in 1999. This was considered too long to wait, as the Air Force needed an interim "2018 bomber" before the 2030s.
To avoid enemy defenses, the 2037 Bomber is expected to fly at extremely high altitude (possibly up to 250,000 ft) and very high supersonic speed (up to Mach 6). It may have the ability to operate unmanned (see Lockheed Martin SR-72 hypersonic aircraft).