The Lockheed U-2 is a reconnaissance/spy aircraft flown by the US Military. It was originally greenlighted by President Eisenhower in the early 1950′s, and was flown exclusively by the CIA at first.

The U-2 was able to fly at 70 ,000 feet, out of the reach of Soviet aircraft and missiles. Original versions of the airplane were outfitted with a high resolution camera that was described as able to see six times more detail than the human eye. It was rumored to be able to spot a newspaper from 70,000 feet.

Because it was able to fly so high, the U-2 was able to fly over the Soviet Union unopposed. As more missions were successful, the US got more brazen, and the Soviets got more angry. Eventually the US planned a mission to fly over the entire breadth of the Soviet Union, a flight that would take over 10 hours. During this mission the pilot was shot down by a Soviet Missile, and captured. (Read more here.)

Because of the extreme altitude of U-2 flights, pilots had to breathe pure oxygen for several hours before take off to purge their bodies of any nitrogen (to prevent hypoxia). Also, due to the thinness of the air, the U-2 top speed and stall speed were only a few knots apart. Pilots had to concentrate to keep the aircraft moving, but not so fast that it would stall.

The U-2 is still flown by the US Military today, but is slated for retirement in the next few years.

Source: History Channel