In 1969, the USAF issued a requirement for a replacement for the  B-52
      with a contract for research, development, test and evaluation awarded
      to Rockwell and General Electric in 1970.  The first B-1 
      prototype flew
      in 1974.  Four prototype
      B-1s were built before President Carter
      cancelled the B-1 program in 1977 in favor of cruise missiles.
      President Reagan resumed the B-1 project in 1981 with a modified
      aircraft designated the B-1B.  The first production  B-1B flew in
      1985.  The B-1 is also known as the "Bone".