An F-106A Delta Dart aircraft rolls along a taxiway at Rockwell International's Plant No. 42, where it has been used as a safety chase aircraft for the B-1B aircraft production acceptance flight test program. The aircraft, which was the final F-106 in active service, will be flown to Davis-Monthan Air Force Base, Arizona, for use in the QF-106 drone program. A B-1B aircraft is in the background

B-1 Lancer is a supersonic variable-sweep wing, heavy bomber built by Rockwell and used by the United States Air Force. It is commonly called the "Bone" (from "B-One"). It is one of three strategic bombers in the U.S. Air Force fleet as of 2018, the other two being the B-2 Spirit and the B-52 Stratofortress. The B-1 was first envisioned in the 1960s as a platform that would combine the Mach 2 speed with the range and payload of the B-52. After a long series of studies, Rockwell International (now part of Boeing) won the design contest for what emerged as the B-1A. This version had a top speed of Mach 2.2 at high altitude and the capability of flying for long distances at Mach 0.85 at very low altitudes. The introduction of cruise missiles and early work on the stealth bombers led to the program being canceled in 1977. The program was restarted in 1981, largely as an interim measure due to delays in the B-2 stealth bomber program, with the B-2 eventually reaching initial operational capability in 1997. This led to a redesign as the B-1B, which differed from the B-1A by having a lower top speed at a high altitude of Mach 1.25, but improved low-altitude performance of Mach 0.96. The electronics were also extensively improved during the redesign, and the airframe was improved to allow takeoff with the maximum possible fuel and weapons load. The B-1B began deliveries in 1986 and formally entered service with Strategic Air Command (SAC) as a nuclear bomber in that same year. By 1988, all 100 aircraft had been delivered. Originally designed for nuclear capabilities, the B-1 switched to an exclusively conventional combat role in the mid-1990s.