The Rockwell (now part of Boeing) B-1 Lancer[N 1] is a four-engine variable-sweep wing strategic bomber used by the United States Air Force (USAF). It was first envisioned in the 1960s as a supersonic bomber with Mach 2 speed, and sufficient range and payload to replace the Boeing B-52 Stratofortress. It was developed into the B-1B, primarily a low-level penetrator with long range and Mach 1.25 speed capability at high altitude.
 

Designed by Rockwell International, the bomber's development was delayed multiple times over its history, as the theory of strategic balance changed from flexible response to massive retaliation and back again. This change in stance repeatedly demanded then ignored the need for manned bombers. The initial B-1A version was developed in the early 1970s, but its production was canceled, and only four prototypes were built. The need for a new platform once again surfaced in the early 1980s, and the aircraft resurfaced as the B-1B version with the focus on low-level penetration bombing. However by this point development of stealth technology was promising an aircraft of dramatically improved capability. Production went ahead as this version would be operational before the "Advanced Technology Bomber", during a period when the B-52 would be increasingly vulnerable. The B-1B entered service in 1986 with the USAF Strategic Air Command as a nuclear bomber.
 

In the 1990s, the B-1B was converted to conventional bombing use. It first served in combat during Operation Desert Fox in 1998 and again during the NATO action in Kosovo the following year. The B-1B has supported U.S. and NATO military forces in Afghanistan and Iraq. The Lancer is the supersonic component of the USAF's long-range bomber force, along with the subsonic B-52 and Northrop Grumman B-2 Spirit. The bomber is commonly called the "Bone" (originally from "B-One"). With the retirement of the General Dynamics/Grumman EF-111A Raven in 1998 and the Grumman F-14 Tomcat in 2006, the B-1B is the U.S. military's only active variable-sweep wing aircraft. The B-1B is expected to continue to serve into the 2030s, when it is to be supplemented by the Next Generation Bomber.