The aircraft division of Rockwell International became the North American Aircraft division, working on the B-1 bomber. The first of four B-1 prototypes flew on Dec. 23, 1974, but the government canceled the program three years later. The next bomber built by North American was was the B-1B, for which Boeing supplied the avionics. It looked like the B-1A, but it had a different mission. The B-1A was designed to penetrate enemy defenses to drop its bombload. The B-1B was a cruise missile carrier, able to launch its missiles a great distance from the target. Although its mission was primarily low-level penetration at high subsonic speeds, the B-1B could fly at supersonic speeds. The B-1B first flew on Oct. 18, 1984, about five months ahead of schedule.