American airmen at the Manas air base, outside Kyrgyzstan's capital, Bishkek, have begun packing. They'll be gone by next summer, together with their fleet of refueling tankers.

These "flying gas stations," as the Air Force informally calls them, patrol Afghanistan's skies 24 hours a day, refueling fighter jets and other NATO military aircraft. Approximately 4,000 times a year, or 11 times per day, refueling sorties lift off from Manas and make the one-hour flight to Afghanistan.

The technology isn't exclusive. Nor is it new: Boeing designed the KC-135 Stratotanker, which is based on the body of a 707, in the 1950s to refuel B-52 bombers. But no one rivals the U.S. military in the number or cost of mid-air refueling missions.