The Rockwell B-1 Lancer[​N 1] is a supersonic variable-sweep wing, heavy bomber used by the United States Air Force. It is commonly called the "Bone" (from "B-One").[​1] It is one of three strategic bombers in the U.S. Air Force fleet as of 2021, the other two being the B-2 Spirit and the B-52 Stratofortress.