Known as the 'Bone', the B-1B began service with the USAF in 1985. The bomber was designed to fly at a minimum speed of Mach 0.85 and as low as 200ft, using terrain-following and terrain-avoidance radar, on penetrating nuclear strikes against the Soviet Union. Its low-altitude and nap-of-the-earth (NOE) flight profile was intended to avoid detection by Soviet ground radar. However, the USSR's development of look-down, shoot-down radar made that mission perilous.
In 1994, with the Cold War over, the USAF eliminated the B-1B's nuclear mission. The bomber found new work with the start of the War on Terror in 2001, flying close air-support missions for the US military in Iraq and Afghanistan. But those missions, which involved slow flying with wings forward–not swept, as intended for penetration strikes–overstressed the B-1B's wings, causing cracks.
A type of very low-altitude flight course.
In nap-of-the-earth flight, a helicopter moves at less than treetop height.