The Lockheed U-2, nicknamed "Dragon Lady", is a single-engine, very high-altitude reconnaissance aircraft operated by the United States Air Force (USAF) and previously flown by the Central Intelligence Agency (CIA). It provides day and night, very high-altitude (70,000 feet / 21,000 meters), all-weather intelligence gathering. The aircraft is also used for electronic sensor research and development, satellite calibration, and satellite data validation.

In the early 1950s, with Cold War tensions on the rise, the U.S. military desired better strategic reconnaissance to help determine Soviet capabilities and intentions. The existing reconnaissance aircraft, primarily bombers converted for reconnaissance duty, were vulnerable to anti-aircraft artillery, missiles, and fighters. It was thought an aircraft that could fly at 70,000 feet (21,000 m) would be beyond the reach of Soviet fighters, missiles, and even radar. This would allow overflights (knowingly violating Soviet airspace) to take aerial photographs.

Under the code name "Bald Eagle", the Air Force gave contracts to Bell Aircraft, Martin Aircraft, and Fairchild Engine and Airplane to develop proposals for the new reconnaissance aircraft. Officials at Lockheed Aircraft Corporation heard about the project and asked aeronautical engineer Clarence "Kelly" Johnson to come up with a design. Johnson was a brilliant designer, responsible for the P-38 Lightning, and the P-80. He was also known for completing projects ahead of schedule, working in a separate division of the company jokingly called the Skunk Works.

Johnson's design, called the CL-282, married long glider-like wings to the fuselage of another of his designs, the Lockheed F-104 Starfighter. To save weight, his initial design did not have conventional landing gear, taking off from a dolly and landing on skids. The design was rejected by the Air Force, but caught the attention of several civilians on the review panel, notably Edwin Land, the father of instant photography. Land proposed to CIA director Allen Dulles that his agency should fund and operate this aircraft. After a meeting with President Eisenhower, Lockheed received a $22.5 million contract for the first 20 aircraft. It was renamed the U-2, with the "U" referring to the deliberately vague designation "utility". The CIA assigned the cryptonym "AQUATONE" to the project.

The first flight occurred at the Groom Lake test site (Area 51) on 1 August 1955, during what was only intended to be a high-speed taxi run. The sailplane-like wings were so efficient that the aircraft jumped into the air at 70 knots (130 km/h).


James Baker developed the optics for a large-format camera to be used in the U-2 while working for Perkin-Elmer. These new cameras had a resolution of 2.5 feet (76 cm) from an altitude of 60,000 feet (18,000 m). Balancing is so critical on the U-2 that the camera had to use a split film, with reels on one side feeding forward while those on the other side feed backward, thus maintaining a balanced weight distribution through the whole flight.

When the first overflights of the Soviet Union were tracked by radar, the CIA initiated Project RAINBOW to reduce the U-2's radar cross section. C.I.A Project Officers determind that the U-2 would have a life of 2 years before the Russian defences would be able to shoot one down and in the late 50's work began on a follow-on aircraft which would fly faster and higher and resulted in the Lockheed A-12 Oxcart program.

Manufacturing was restarted in the 1980s to produce TR-1/U-2R aircraft which was about 40% larger than the original U-2's

The unique design that gives the U-2 its remarkable performance also makes it a difficult aircraft to fly. It was designed and manufactured for minimum airframe weight, which results in an aircraft with little margin for error. Most aircraft were single-seat versions, with only five two-seat trainer versions known to exist. Early U-2 variants were powered by Pratt & Whitney J57 turbojet engines. The U-2C and TR-1A variants used the more powerful Pratt & Whitney J75 turbojet. The U-2S and TU-2S variants incorporated the even more powerful General Electric F118 turbofan engine.

High-aspect-ratio wings give the U-2 some glider-like characteristics, with a lift-to-drag ratio estimated in the high 20s. To maintain their operational ceiling of 70,000 feet (21,000 m), the U-2A and U-2C models (no longer in service) must fly very near their maximum speed. The aircraft's stall speed at that altitude is only 10 knots (19 km/h) below its maximum speed. This narrow window was referred to by the pilots as the "coffin corner". For 90% of the time on a typical mission the U-2 was flying within only five knots above stall, which might cause a decrease in altitude likely to lead to detection, and additionally might overstress the lightly built airframe.

The U-2's flight controls are designed around the normal flight envelope and altitude that the aircraft was intended to fly in. The controls provide feather-light control response at operational altitude. However, at lower altitudes, the higher air density and lack of a power-assisted control system makes the aircraft very difficult to fly. Control inputs must be extreme to achieve the desired response in flight attitude, and a great deal of physical strength is needed to operate the controls in this manner.

The U-2 is very sensitive to crosswinds which, together with its tendency to float over the runway, makes the U-2 notoriously difficult to land. As the aircraft approaches the runway, the cushion of air provided by the high-lift wings in ground effect is so pronounced that the U-2 will not land unless the wing is fully stalled. To assist the pilot, the landing U-2 is paced by a chase car (usually a "souped-up" performance model including a Ford Mustang SSP, Chevrolet Camaro B4C, Pontiac GTO, and the Pontiac G8 GT) with an assistant (another U-2 pilot) who "talks" the pilot down by calling off the declining height of the aircraft in feet as it decreases in airspeed.

Instead of the typical tricycle landing gear, the U-2 uses a bicycle configuration with a forward set of main wheels located just behind the cockpit, and a rear set of main wheels located behind the engine. The rear wheels are coupled to the rudder to provide steering during taxiing. To maintain balance while taxiing, two auxiliary wheels, called "pogo's" are added for takeoff. These fit into sockets underneath each wing at about mid-span, and fall off during takeoff. To protect the wings during landing, each wingtip has a titanium skid. After the U-2 comes to a halt, the ground crew re-installs the pogo's one wing at a time, then the aircraft taxis to parking.

Because of the high operating altitude, the pilot must wear the equivalent of a space suit. The suit delivers the pilot's oxygen supply and emergency protection in case cabin pressure is lost at altitude (the cabin provides pressure equivalent to about 29,000 feet / 8,800 meters). To prevent hypoxia and decrease the chance of decompression sickness, pilots don a full pressure suit and begin breathing 100% oxygen one hour prior to launch to remove nitrogen from the body; while moving from the building to the aircraft they breathe from a portable oxygen supply.

The aircraft carries a variety of sensors in the nose, Q-bay (behind the cockpit, also known as the camera bay), and wing pods. The U-2 is capable of simultaneously collecting signals, imagery intelligence and air samples. Imagery intelligence sensors include either wet film photo, electro-optic or radar imagery – the latter from the Raytheon ASARS-2 system. It can use both line-of-sight and beyond-line-of-sight data links. One of the most unusual instruments in the newest version of the U-2 is the off-the-shelf Sony video camera that functions as a digital replacement for the purely optical view sight (an upside down periscope-like viewing device) that was used in older variants to get a precise view of the terrain directly below the aircraft, especially during landing.

Though the U.S. Air Force and Navy through the  EPX test program would eventually fly the U-2, it was originally a CIA operation, run through the Office of Scientific Intelligence. Due to the political implications of a military aircraft invading a country's airspace, only CIA U-2's conducted overflights. The pilots had to resign their military commissions before joining the CIA as civilians, a process they referred to as "sheep dipping". As with CIA involvement, besides the normal construction and serial number for each aircraft produced, each U-2 also has an "Article Number" assigned, and each U-2 would be referred to with its article number on classified internal documents/memos. Another user of the U-2 was the Republic of China flying under the 35 Squadron and in co-operation of DET H / C.I.A

As often happens with new aircraft designs, there were several operational accidents, some fatal. The first fatal accident was on 15 May 1956, when the pilot stalled the aircraft during a post-takeoff manoeuvre which was intended to drop off the wingtip outrigger wheels. The second occurred three months later, on 31 August when the pilot stalled the aircraft immediately after takeoff. Two weeks later, a third aircraft disintegrated during ascent, also killing the pilot. There were a number of other non-fatal incidents, including at least one which resulted in the loss of the aircraft.

Once U-2 C.I.A units became operational, two units were deployed to Europe and one to the Far East. The first U-2 overflight of the Soviet Union occurred on 4 July 1956. Leaving from Wiesbaden, Germany, the pilot Harvey Stockman flew over Poland, Belorussia, and the Soviet Baltic, before returning to Wiesbaden. In 1957, one of the European units was based at the Giebelstadt Army Airfield, Germany, and the Far Eastern unit was based at the Naval Air Facility Atsugi, Japan.

The U-2 came to public attention when CIA pilot Gary Powers was shot down over Soviet territory on 1 May 1960, causing the U-2 incident.

On 14 October 1962, a U-2 from the 4080th Strategic Reconnaissance Wing, based at Laughlin Air Force Base near Del Rio, Texas, and piloted by Major Richard S. Heyser, photographed the Soviet military installing nuclear warhead missiles in Cuba, precipitating the Cuban Missile Crisis. Heyser concluded this flight at McCoy AFB in Orlando, Florida, where the 4080th established a U-2 operating location for the duration of the crisis. On 27 October 1962, in flight from McCoy AFB, a U-2 was shot down over Cuba by two SA-2 Guideline surface-to-air missiles, killing the pilot, Major Rudolf Anderson, Jr. Anderson was posthumously awarded the first Air Force Cross.

In 1963, the CIA started project Whale Tale to develop carrier-based U-2Gs to overcome range limitations. During development of the capability, CIA pilots took off and landed U-2Gs on the aircraft carrier USS Ranger and other ships. The U-2G was used only twice operationally. Both flights occurred from USS Ranger in May 1964 to observe France's development of an atomic bomb test range at Moruroa in French Polynesia.

In early 1964, the Strategic Air Command (SAC) sent a detachment of U-2s from the 4080th to South Vietnam for high-altitude reconnaissance missions over North Vietnam. On 5 April 1965, U-2s from the 4028th SRS (Strategic Reconnaissance Squadron) took photos of SAM-2 sites near Hanoi and Haiphong harbour. On 11 February 1966, the 4080th Wing was re-designated the 100th SRW and moved to Davis-Monthan AFB, Arizona. The SRS detachment at Bien Hoa AB, South Vietnam, was re-designated the 349th SRS.

The only loss of a U-2 during combat operations occurred on 8 October 1966, when Major Leo Stewart, flying with the 349th Strategic Reconnaissance Squadron, developed mechanical problems high over North Vietnam. The U-2 managed to return to South Vietnam where Stewart ejected safely. The U-2 crashed near its base at Bien Hoa. In July 1970, the 349th SRS at Bien Hoa moved to Thailand and was re-designated the 99th SRS, remaining there until March 1976.In 1969, the larger U-2Rs were flown from the aircraft carrier USS America. The U-2 carrier program is believed to have been halted after 1969.

In June 1976, the U-2s of the 100th SRW were transferred to the 9th SRW at Beale Air Force Base, California, and merged with SR-71 aircraft operations there. When Strategic Air Command was disestablished in the early 1990s, the wing was transferred to the new Air Combat Command (ACC) and re-designated the 9th Reconnaissance Wing (9 RW).

In 1977, a U-2 was retrofitted with an upward-looking window so that it could be used for high-altitude astronomical observations of the cosmic microwave background (CMB). This experiment was the first to measure definitively the motion of the galaxy relative to the CMB, and established an upper limit on the rotation of the universe as a whole.

In 1984, during a major NATO exercise, Royal Air Force Flight Lieutenant Mike Hale intercepted a U-2 at a height of 66,000 feet (20,000 m), where the aircraft had previously been considered safe from interception. Hale climbed to 88,000 feet (27,000 m) in his Lightning F3.

In 1989, a U-2R of 9 RW, Detachment 5, flying out of Patrick Air Force Base, Florida successfully photographed a space shuttle launch for NASA to assist in identifying the cause of tile loss during launch discovered in the initial post-Challenger missions.

On 19 November 1998, a NASA ER-2 research aircraft set a world record for altitude of 20,479 metres (67,188 ft) in horizontal flight in the 12,000 kilograms (26,000 lb) to 16,000 kilograms (35,000 lb) weight class

The U-2 remains in frontline service more than 50 years after its first flight despite the advent of surveillance satellites. This is primarily due to the ability to direct flights to objectives at short notice, which satellites cannot do. The U-2 has outlasted its Mach 3 SR-71 replacement, which was retired in 1998.

A classified budget document approved by the Pentagon on 23 December 2005 called for the termination of the U-2 program no earlier than 2012, with some aircraft being retired by 2007. In January 2006, Secretary of Defence Donald Rumsfeld announced the pending retirement of the U-2 fleet as a cost-cutting measure, and as part of a larger reorganization and redefinition of the Air Force's mission that includes the elimination of all but 56 B-52s and a complete reduction in the Lockheed F-117 Nighthawk fleet Rumsfield  said that this will not impair the Air Force's ability to gather intelligence, which will be done by satellites and a growing supply of unmanned RQ-4 Global Hawk reconnaissance aircraft.

Proposals to retire the U-2 have been met with significant resistance from military leadership due to gaps in capability that would present if the U-2 were removed from service. In 2009, the Air Force stated that it plans to extend the U-2 retirement from 2012 until 2014 or later to allow more time to field the RQ-4 Global Hawk as a replacement. In December 2009, South Korea's JoongAng Daily newspaper reported that the RQ-170 Sentinel was to replace U-2s operating from Osan Air Base in 2010.

There are current reports that the U-2 has enjoyed a new lease on life in Afghanistan. Since being fitted with new sensors and communications equipment, it has become an indispensable eye-in-the-sky for NATO forces. The high-resolution camera is capable of spotting slight changes in the country’s dry mud paths where the Taliban often bury improvised explosive devices (IEDs). As of early 2010, U-2s from the 99th Expeditionary Reconnaissance Squadron have flown over 200 missions in support of Operations Iraqi Freedom and Enduring Freedom; as well as Combined Joint Task Force – Horn of Africa.

A U-2 is stationed in Cyprus in March 2011 to help in the enforcement of the no-fly zone over Libya, and a U-2 stationed at Osan Air Base in South Korea was used to provide imagery of the Japanese nuclear reactor damaged by the 11 March 2011 earthquake and tsunami.

In March 2011, it was projected that the US's fleet of 32 U-2s would be operated until 2015. The Obama administration requested $91 million to maintain the U-2