Rockwell International maintenance personnel stand in front of an F-106A Delta Dart aircraft prior to its last flight. The aircraft, which was the last Delta Dart in active service, has been used as a safety chase aircraft in the B-1B aircraft production acceptance flight test program. It will be taken to Davis-Monthan Air Force Base, Arizona, where it will become a QF-106 drone aircraft. A B-1B aircraft is in the background

The X-planes are a series of experimental United States aircraft and rockets, used to test and evaluate new technologies and aerodynamic concepts. They have an X designator, which indicates the research mission within the US system of aircraft designations. The first, the Bell X-1, became well known in 1947 after it became the first aircraft to break the sound barrier in level flight. Most of the X-planes have been operated by the National Advisory Committee for Aeronautics (NACA) or, later, the National Aeronautics and Space Administration (NASA), often in conjunction with the United States Air Force. The majority of X-plane testing has occurred at Edwards Air Force Base. Some of the X-planes have been well publicized, while others have been developed in secrecy. Most X-planes are not expected to go into full-scale production.

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.