Began development in 1954 under the Eisenhower administration following the discovery of the need for an overhead imagery asset that could not be interfered with. Designated as Project AQUATONE, the aircraft began operations in 1956 after which it immediately began overflights of the Soviet Union to acquire imagery of targets therein. Most operations over the Soviet Union began from the U-2's then primary base in Adana, Turkey where a cover squadron operating under the guise of being a weather observation unit was stationed.
On May 1, 1960 the U-2 achieved a certain public fame the United States had wished to avoid with it's intelligence collection efforts when the aircraft piloted by Francis Gary Powers was shot down over central Russia. The mission, (which was supposed to have ended in Norway,) terminated when surface to air missiles recently developed and fielded specifically to counter the blatant aerial invasion of Soviet airspace by the U-2 found their target. Following an unsuccessful attempt to destroy the aircraft, Powers ejected and survived to face trial and conviction on espionage charges. He was later repatriated to the United States, where after working for Lockheed/Martin's Skunkworks black project division was killed while piloting a traffic helicopter in the mid-1980's. (Note: The Central Intelligence Agency for whom Powers was working was not at all a group of happy campers when he was shot down. There has been some rumor from the conspiracy theorists that Powers was assassinated for his failure to destroy the plane and commit suicide in the process. Interestingly enough, Lockheed was impressed enough with his piloting skills to employ him testing other variants of the U-2 for several years.)
The current variant of the U-2 in service today is the U-2R. Wingspan of 103 feet, length 63 feet and height of 16 feet. Operational service ceiling in excess of 70,000 feet, cruise speed 530 knots at 45,000 feet with 3,000 mile range. Flexible mission oriented sensor package including the H Camera system capable of twelve to eighteen inch range at 35-40 nautical miles. Can also be equipped with the Optical Bar Camera which uses a 30-inch focal length camera capable of 6-inch resolution of targets at similar distances to the H Camera. Both systems are capable of slant photography, i.e. when overflight or intrusion into airspace is impractical the aircraft can fly along a border and acquire imagery of a target given that it is located within range. U-2R's utilize an ASARS (Advanced Synthetic Aperture Radar,) system for standoff imagery of targets when either weather or threat environment nullifies the ability to make visual acquisition of the subject target.
Public sources:
The U.S. Intelligence Community, Third Edition. Jeffery T. Richelson 1995, pgs. 158-159.
A&E Biography: Francis Gary Powers. Originally aired late 1999.