The Lockheed U-2, nicknamed Dragon Lady, is a single-seat, single-engine, high-altitude surveillance aircraft flown by the United States Air Force. It provides continuous day and night, high-altitude (70,000 ft, 21,000 m plus), all-weather surveillance of an area in direct support of U.S. and allied ground and air forces. It also provides critical intelligence to decision-makers through all phases of conflict, including peacetime indications and warnings, crises, operations other than war, and major theater war. The aircraft are also used for electronic sensor research and development, satellite calibration, and satellite data validation.

The U-2 is still in front-line service over 50 years after its first flight. Production of new aircraft was restarted in the 1980s. It has outlasted its Mach 3 SR-71 replacement which was retired in 1998. A classified budget document approved by the Pentagon on December 23, 2005, calls for the termination of the U-2 program no earlier than 2011, with some aircraft being retired as early as 2007. The U-2 would likely be supplanted by the Northrop Grumman's high-altitude Global Hawk unmanned aerial vehicle.

The Lockheed U-2, model number CL-282, was developed under the project name "Aquatone." Its official designation could not use B for bomber and F for fighter because its purpose was strictly reconnaissance. Since the project was under tight secrecy, it could not be designated as a reconnaissance aircraft. In order to conceal its true mission, the Air Force elected to apply the "utility" designation, and the CL-282 became the U-2.

Initially, Clarence "Kelly" Johnson adapted the F-104 Starfighter, replacing the low aspect ratio wings with extremely large glider type wings as a starting point.
High aspect ratio wings give the U-2 some glider-like characteristics. The aircraft is extremely challenging to fly, not only due to its unusual landing characteristics, but also because of the extreme altitudes it can reach. To maintain its operational ceiling of 70,000 feet, the U-2A and U-2C models (no longer in service) must fly very near their maximum speed (critical mach). However, the aircraft's (stall speed) at that altitude is only five knots (9 km/h) less than its maximum speed. For 90% of the typical mission, the U-2 pilot is flying within only five knots of a stall, which would constitute an unacceptable decrease in altitude, and consequently, detection.


Because of its high-altitude mission, 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 approximately 29,000 feet (8800 m)). To prevent hypoxia and decrease the chance of decompression sickness, pilots don an S1034 full pressure suit (manufactured by the David Clark Company) and begin breathing 100% oxygen one hour prior to launch; while moving from the building to the aircraft they breathe from a portable liquid oxygen supply.

The U-2 is considered one of the most challenging aircraft in the military inventory to fly and requires a high degree of airmanship from its pilots. Its large wingspan and resulting glider-like characteristics make the U-2 highly sensitive to crosswinds. This sensitivity, and the aircraft's tendency to float over the runway, makes the U-2 notoriously difficult to land. Typically, a second U-2 pilot, designated as the mission's backup pilot and referred to as the "mobile", waits in a high-performance chase car (currently a Chevrolet Camaro or Pontiac GTO) at the end of the runway as the aircraft makes it landing approach. As the U-2 passes, the chase car follows it at high speed, with the mobile calling out the aircraft's altitude via radio to the pilot. When the aircraft's main landing gear is within approximately two feet of the runway surface the pilot deploys spoilers located on the top of the wings to reduce lift (spoiling the lift and increasing the stall speed by 2 knots). Speed brakes also deploy from the fuselage behind the wing, and increase drag to slow the aircraft down.
The flap system is unique, and has the ability to reduce lift in a gust mode (5 degrees up).

Another distinguishing characteristic of the U-2 is its landing gear. Instead of the typical tricycle configuration consisting of a nose wheel and two sets of main wheels under each wing, the U-2 uses a bicycle configuration consisting of one set of main wheels located just behind the cockpit and one set of rear wheels located behind the engine that are tied to the rudder and provide the steering. To maintain balance and allow the aircraft to taxi, two sets of auxiliary wheels called "pogos" are installed under each wing by ground crew. The pogos fall out of sockets in the wing and onto the runway surface when the aircraft takes off. The ground crew collects the pogos and re-installs them after the aircraft lands. U-2 ground crews, in a spirit of playfulness, often say that the pogos are installed from the back of a pick-up truck that drives alongside the aircraft while it is moving at high speed down the runway. In fact, the pogos are installed after the aircraft has come to a full stop with one wing dropped onto the ground. Skids made of titanium strips are located on the bottom of each wing tip to protect the "heavy" or downed wing. The ground crew install the a pogo in the "light" or up wing first. Then two of the crew will use their weight to pull the light wing down, allowing the third crew member to install the pogo on the other side. Occasionally it is difficult to lift the "down" wing, either because of a fuel imbalance, or because the pogo is not correctly set into the wing, in which case the ground crew is used as a counterweight by riding the other wingtip with the working pogo, and balancing the aircraft. The aircraft taxis under its own power back to its parking location.

The aircraft carries a variety of sensors in the nose, Q-bay or 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.

The aircraft completed an upgrade to the General Electric F118-101 engine in 1998, primarily to increase maintainability by replacing the aging Pratt & Whitney J75 engine that had first been developed in the 1950s. Significant side benefits of the newer GE engine were better fuel economy, reduced weight and increased power. To increase longevity the GE engine was derated to roughly match the output from the PW engine. Other upgrades to the sensors and the addition of the Global Positioning System increased collection capability and provided superimposed geo-coordinates directly on collected images.

The U-2R, first flown in 1967, is significantly larger and more capable than the original aircraft. A tactical reconnaissance version, the TR-1A, first flew in August 1981. A distinguishing feature of these aircraft is the addition of a large instrumentation "superpod" under each wing. Designed for standoff tactical reconnaissance in Europe, the TR-1A was structurally identical to the U-2R. The 17th Reconnaissance Wing, Royal Air Force Station Alconbury, England used operational TR-1As from 1983 until 1991. The last U-2 and TR-1 aircraft were delivered to the Air Force in October 1989. In 1992 all TR-1s and U-2s (all U-2Rs) were designated U-2Rs. The two-seat trainer variant of the TR-1, the TR-1B, was redesignated as the TU-2R. After upgrading with the F-118-101 engine, the former U-2Rs were designated the U-2S Senior Year.

A derivative of the U-2 known as the ER-2 (Earth Resources -2) is used by the National Aeronautics and Space Administration for high altitude civilian research including Earth resources, celestial observations, atmospheric chemistry and dynamics, and oceanic processes.

U-2A — The first production model of the U-2 spy plane; J57-P-37A engine.

WU-2A — Weather, atmospheric research aircraft.

U-2B — Improved production version; J57-P-31 engine.

U-2C — Improved production version; J75-P-13 engine.

U-2CT — Two-seat training version.

U-2D — Two-seat high-altitude research aircraft.

U-2EPX — Proposed maritime surveillance version for the U.S. Navy.

U-2R (TR-1) — larger wing and fuselage, J75-P-13B engine; "superpod" instrument pods under wings

U-2S — R with F118-GE-101 engine.