The bizarre, jagged-triangle shape of the B-2 long-range bomber is part of its "stealth" design, which uses various technologies to minimise its appearance to enemy radar.
Where previously bomber crews have had to train to fly very low to try to evade enemy radar detection, the idea behind the four-engine B-2 is that its stealth allows it to operate at high altitude.
This gives it a better range and more scope for finding and attacking targets.
At a cost about $1.3bn each, only 22 B-2s have been built, with 16 assigned to combat.
A drawback is that the aircraft's stealth coating needs repair after each mission - although the air force says the problems this causes are exaggerated and maintenance has been done without its special climate-controlled hangar.
Three pairs took part in the first three days of attacks on Afghanistan, flying from their home at Whiteman Air Force Base, Missouri, and refuelling in flight several times on the way.
With a subsonic top speed, each mission lasted more than 40 hours. One, at 44 hours, is said to have been the longest combat sortie in aviation history. The two pilots take it in turns to have brief "power naps".
Flights began at Whiteman, attacked Afghanistan, and carried on to the British island of Diego Garcia in the Indian Ocean. With a fresh aircrew the planes then made the 30-hour flight home.
The commander of the 509th Bomber Wing said the fact that the planes did not shut down their engines for more than 70 hours highlighted their reliability.
But such long missions put a strain on the available aircrew.
B-2s can carry some 40,000 lb (18,140 kg) of nuclear or conventional bombs and, over Kosovo, were the first to use the new JDAM satellite-guided bomb.
40,000 pounds (18,144 kgs) of conventional or nuclear weapons