The Lockheed U-2, nicknamed "Dragon Lady", is a single-engine, 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 m), all-weather intelligence gathering.[1] The U-2 has also been used for electronic sensor research, satellite calibration, and communications purposes.

The U-2 has prominently featured in several events during the Cold War, at stages of which U-2s commonly overflew the Soviet Union, the People's Republic of China, North Vietnam, and Cuba. In 1960, CIA pilot Gary Powers was shot down while flying a U-2 over Soviet territory. In 1962, a U-2 piloted by Major Rudolf Anderson, Jr. was shot down over Cuba by surface-to-air missiles during the Cuban missile crisis.

The U-2 has remained in service since the end of the Cold War and is one of several aircraft types that have been operated by the USAF in excess of 50 years. It has participated in conflicts such as Afghanistan and Iraq, and supported several multinational NATO operations. The role of the U-2 is increasingly performed by alternative platforms, such as surveillance satellites, unmanned reconnaissance drones such as the Northrop Grumman RQ-4 Global Hawk, and conventional aircraft.

Development
Background
After World War II the U.S. military desired better strategic reconnaissance to help determine Soviet capabilities and intentions. Into the 1950s the best intelligence the American government had on the interior of the Soviet Union was German Luftwaffe photographs taken during the war of territory west of the Ural Mountains, so overflights to take aerial photographs of the Soviet Union began. After 1950 Soviet air defenses aggressively attacked all aircraft near its borders—sometimes even those over Japanese airspace—and the existing reconnaissance aircraft, primarily bombers converted for reconnaissance duty such as theRB-47, were vulnerable to anti-aircraft artillery, missiles, and fighters. Richard Leghorn of the United States Air Force suggested that an aircraft that could fly at 60,000 feet should be safe from the MiG-17, the Soviet Union's best interceptor, which could barely reach 45,000 feet. He and others believed that Soviet radar, which used American equipment provided during the war, could not track aircraft above 65,000 feet.

The highest-flying aircraft available to America and its allies at the time was the English Electric Canberra, which could reach 48,000 feet. The British had already produced the PR3 photo-reconnaissance variant, but the USAF asked English Electric's help to help further modify the Martin B-57—the American licensed version of the Canberra—with long, thin wings, new engines, and a lighter-than-normal airframe to reach 67,000 feet during flight. Air Research and Development Command mandated changes to the design which, although they made the aircraft more durable during wartime, meant that the resulting RB-57D aircraft of 1955 could only reach 64,000 feet. The Soviet Union, unlike the United States or Britain, had also improved radar technology after the war, and could track aircraft above 65,000 feet.

Lockheed proposal
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 radar. Another U.S. Air Force officer, John Seaberg, wrote in 1953 a request for proposal for an aircraft that could reach 70,000 feet over a target with 1,500 nautical miles of operational radius. The USAF decided to only solicit designs from smaller aircraft companies that could give the project more attention. Under the code name "Bald Eagle", it gave contracts to Bell Aircraft, Martin Aircraft, and Fairchild Engine and Airplane to develop proposals for the new reconnaissance aircraft. Officials atLockheed Aircraft Corporation heard about the project and decided to submit an unsolicited proposal. To save weight and increase altitude, Lockheed executive John H. Carter suggested that the design eliminate landing gear and avoid attempting to meet combat load factors for the airframe. The company asked Clarence "Kelly" Johnson to come up with such a design. Johnson was Lockheed's best aeronautical engineer, responsible for the P-38, 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, attached long glider-like wings to the fuselage and General Electric J73 engine of another of his planes, the Lockheed F-104 Starfighter. The aircraft, essentially a jet-powered glider, took off from a dolly and landed on skids, and could reach 70,000 feet in altitude with a 2,000-mile range. In June 1954 the USAF rejected the design in favor of the Bell X-16 and the modified B-57. Reasons included the lack of landing gear, usage of the J73 engine instead of the more proven Pratt & Whitney J57 like the competing designs, and not using multiple engines which, the USAF believed, was more reliable. (General Curtis LeMay of Strategic Air Command (SAC) walked out during a CL-282 presentation, saying that he was not interested in an airplane without wheels or guns.)

Approval
Civilian officials such as Trevor Gardner, an aide to Secretary of the Air Force Harold E. Talbott, were more positive on the CL-282 because of its higher potential altitude and smaller radar cross section, and recommended the design to the Central Intelligence Agency (CIA)'s Office of Scientific Intelligence. At this time the CIA depended on the military for overflights, and Director of Central Intelligence (DCI) Allen Dulles favored human over technical intelligence gathering methods. However, the Intelligence Systems Panel, a civilian group advising the USAF and CIA on aerial reconnaissance, by 1954 recognized that the RB-57D would not meet the 70,000-feet requirement that panel member Allen Donovan ofCornell Aeronautical Laboratory believed was necessary for safety. The CIA told the panel about the CL-282, and the aspects of its design that the USAF saw as flaws—the single engine and light load factor—appealed to Donovan, a sailplane enthusiast who believed that a sailplane was the type of high-altitude aircraft the panel was seeking.

Edwin Land, the father of instant photography and another member of the panel, proposed to Dulles through Dulles' aide Richard M. Bissell, Jr. that his agency should fund and operate this aircraft. Land believed that the military operating the CL-282 during peacetime could provoke a war. Although Dulles remained reluctant to have the CIA conduct its own overflights, Land and James Killian of MIT told President Eisenhower about the aircraft; Eisenhower agreed that the CIA should be the operator. Dulles finally agreed, but some U.S. Air Force officials opposed the project because they feared it would endanger the RB-57D and X-16. The USAF's Seaberg helped persuade his own agency to support the CL-282, albeit with the higher-performance J57 engine, and final approval for a joint USAF-CIA project—the first time the CIA dealt with sophisticated technology—came in November 1954. Lockheed had meanwhile become busy with other projects and had to be persuaded to accept the CL-282 contract after approval.

Manufacture
Bissell became head of the project, which used covert funding. (Under the Central Intelligence Agency Act of 1949, the DCI is the only federal government employee who can spend "un-vouchered" government money.) Lockheed received a $22.5 million contract in March 1955 for the first 20 aircraft, with the first $1.26 million mailed to Johnson's home in February 1955 to keep work going during negotiations. The company agreed to deliver the first aircraft by July of that year and the last by November 1956. It did so, and for $3.5 million under budget, because the aircraft was based on the F-104; only the wings and tail were different.

Procurement of the aircraft's components occurred secretly. When Johnson ordered altimeters calibrated to 80,000 feet from a company whose instruments only went to 45,000 feet, the CIA set up a cover story involving experimental rocket aircraft. Shell Oil developed a new low-volatility, low vapor pressure jet fuel that would not evaporate at high altitudes; the fuel became known as JP-7, and manufacturing several hundred thousand gallons for the aircraft in 1955 caused a nationwide shortage of Shell's Flit insect repellant. The aircraft was renamed the U-2 in July 1955, the same month the first aircraft, Article 341, was delivered to Groom Lake. The "U" referred to the deliberately vague designation "utility" instead of "R" for "reconnaissance", and the U-1 and U-3 aircraft already existed. The CIA assigned the cryptonym "Aquatone" to the project, with the USAF using the name "Oilstone" for their support to the CIA.

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). The aircraft was so crowded that when Baker asked Johnson for six more inches of space for a lens of 240-inch focal length, Johnson replied "I'd sell my grandmother for six more inches!"; Baker instead used a 180-inch f/13.85 lens in a 13" by 13" format for his final design. 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 fed 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. This effort ultimately proved unsuccessful, and work began on a follow-on aircraft, which resulted in the Lockheed A-12 Oxcart. Manufacturing was restarted in the 1980s to produce the TR-1, an updated and modernized design of the U-2.

Design
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 J75turbojet. 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 an engine out glide ratio of about 23:1, comparable to gliders of the time. To maintain their operational ceiling of 70,000 feet (21,000 m), the U-2A and U-2C models (no longer in service) had to fly very near their Never exceed speed (VNE). The margin between that speed and its stall speedat that altitude is only 10 knots (12 mph; 19 km/h) below its maximum speed. This narrow window was referred to by the pilots as the "coffin corner",because breaching either limit would likely cause the wings or tail to fall off the delicate plane. 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 at which the aircraft was intended to fly. 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 aircraft notoriously difficult to land. As it 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. A landing U-2 is accompanied on the ground by a chase car and an assisting U-2 pilot calling off the angles and declining aircraft height as the aircraft descends. Cars used have been Ford Mustang SSP, Chevrolet Camaro B4C, Pontiac GTO, Dodge Charger Police Package, Pontiac G8 GT, and Chevrolet Camaro SS.

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 "pogos" 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 pogos one wing at a time, then the aircraft taxis to parking.

Because of the high operating altitude and the cockpit's partial pressurization, equivalent to 28,000 feet, the pilot wears a partially pressurized space suit, which delivers the pilot's oxygen supply and provides emergency protection in case cabin pressure is lost. While pilots can drink water and eat food in squeezable containers through a self-sealing hole in the face mask, they typically lose up to six pounds of weight on a eight-hour mission. Most pilots chose to not take with them the suicide pill offered before missions. If put in the mouth and bitten, the "L-pill"—containing liquid potassium cyanide—would cause death in 10 to 15 seconds. After a pilot almost accidentally ingested an L-pill instead of candy during a December 1956 flight the suicide pills were put into boxes to avoid confusion. When in 1960 the CIA realized that a pill breaking inside the cockpit would kill the pilot, it destroyed the L-pills and its Technical Services Division developed a needle poisoned with a powerful shellfish toxin and hidden in a silver dollar. Only one was made because, as the agency decided, if any pilot needed to use it the program would probably be canceled.

To prevent hypoxia and decrease the chance of decompression sickness, pilots begin breathing 100% oxygen an hour prior to take off to remove nitrogen from the body; a portable oxygen supply is used prior to entering the aircraft.[29] Since 2001, more than a dozen pilots have been reported to have suffered the effects of decompression sickness, including permanent brain damage in nine. Initial symptoms include becoming suddenly unable to read, and disorientation. Factors increasing the risk of illness since 2001 included longer mission durations and more cockpit activity. Conventional reconnaissance missions would limit pilot duties to maintaining flight path for camera photography; operations over Afghanistan included more real time activities, such as communication with ground troops, increasing their bodies' oxygen requirements and the risk of nitrogen bubble formation. The USAF is studying the issue; U-2 pilots now exercise during oxygen pre-breathing. Among other remedies proposed is an increased cockpit pressurization to a 15,000 feet equivalent. In 2013, modifications were initiated under the Cockpit Altitude Reduction Effort (CARE), to beef up the cockpit structure. This will allow the cockpit cabin pressure to be increased from 3.88 psi to 7.65 psi, lowering the cockpit pressurization to a 15,000 feet equivalent. In addition, the urine collection device was rebuilt as part of CARE to eliminate corrosion caused by leakage.

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 viewsight (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.