Reconnaissance Summary

  • Last updated on November 10, 2022

The military exploration of enemy territory to gain strategic information.

History and Development

Aerial reconnaissance was the first mission of combat aviation, from which all other combat missions were outgrowths. Since their humble beginnings in World War I (1914-1918), when pilots flew over battlefields looking for the enemy, reconnaissance aircraft, their sensors, and their missions have evolved in directions that would have been unimaginable to those pioneers in their flimsy aircraft over no-man’s-land.

By the late twentieth century, the most frequently used battlefield reconnaissance aircraft were scout helicopters, such as the OH-58, which fly at low altitudes, following the terrain to minimize their vulnerability. These aircraft look for artillery targets and information for the divisional intelligence staff and flush out victims for attack helicopters. High-performance fighters are unsuited for these vital and dangerous missions, which require aircraft that can move slowly enough to find targets as small as a single vehicle or group of soldiers and can hover over the battlefield long enough to make a difference.

At an echelon above the battlefield scouts are high-performance reconnaissance aircraft, generally modified fighter aircraft. In World War II (1939-1945), they tended to be stripped-down versions of the fastest aircraft available, such as the F-5, a modified P-38 Lightning, or the De Havilland Mosquito. Their speed and high-altitude performance usually allowed them to evade pursuit and to avoid flak. Two primary missions of high-performance reconnaissance aircraft during this period were finding targets for strategic bombers and reporting on the results of bombing raids.

With the introduction of satellites and more specialized strategic reconnaissance aircraft, the modified fighter declined in prominence and now primarily supports the intelligence-gathering needs of the theater commander. Thus, the modified fighter reconnaissance aircraft no longer has the best available airframe. In recent decades, aircraft types have remained in service for reconnaissance long after they have been replaced as fighters. A prime example, the RF-4C Phantom, flew reconnaissance missions for the U.S. Air Force for more than a decade after the F-4 fighter was retired from the active inventory. Although these aircraft can mount a variety of sensors, including side-looking airborne radar (SLAR), their primary tool is usually photography.

During the Cold War, the modified fighter was phased out of strategic reconnaissance missions. Because it had never been feasible to send a modified fighter deep into the interior of the Soviet Union, this region remained a total mystery to the West at the start of the Cold War. During the early 1950’s, nations of the North Atlantic Treaty Organization (NATO) routinely learned about new Soviet weapons systems only after they had been paraded across Moscow’s Red Square on the May Day holiday. The first effective U.S. attempt to address this problem was the U-2, a low-speed, high-altitude aircraft with a ceiling of 70,000 feet. Stategists hoped that the U-2 would fly high enough to avoid any possibility of intercept. The U-2 succeeded at its mission from 1956 until 1960, when an SA-2 brought one down with disastrous political consequences.

The next stage in the development of strategic reconnaissance aircraft was the SR-71. Its existence was first made public in 1964, and it officially remains the fastest airplane in the world. To this day, the SR-71 has never been successfully intercepted, and it remains outside the altitude and speed envelopes of the most capable surface-to-air missiles.

During the late 1940’s, it was realized that the most effective solution to the strategic reconnaissance problem was the Earth-circling satellite, but it was many years before the technology was implemented. In August, 1960, a satellite, launched under the name Project Corona, took the first photograph from space. By the 1970’s, both the United States and the Soviet Union had routinely deployed a broad array of surveillance satellites. Satellites initially used cameras, which would jettison their film after their mission was completed. A recovery aircraft would then snag the film capsule in midair as it drifted down to Earth.

With time, further sensors have been added to satellites to include infrared and electronic intercept capabilities, and encrypted satellite downlinks have removed the need for midair recovery of falling film canisters. Satellites, however, continue to be hindered by their predictable and difficult-to-change orbits and by their limited ability to see targets that are obscured by the effects of clouds and other atmospheric conditions.

The Intelligence Process

Aerial reconnaissance, although extremely important, is not the only tool available to the intelligence analyst. Intelligence can be described as a mosaic, in which each aerial image, communications intercept, or spy report is a piece. Although each piece, in itself, might not reveal much information, when placed in the context of all other intelligence from all other available sources, the pieces come together to form a coherent picture. Each intelligence source has its own complementary strengths and weaknesses.

Human Intelligence

Human intelligence (HUMINT) is information gained from human beings: spies, prisoners of war, scouts, or combatants in contact with the enemy. In an airborne context, human intelligence usually consists of spot reports of visual sightings by pilots or observers. On the modern battlefield, with video feeds to ground stations becoming increasingly common, the line between human intelligence and imagery intelligence has become somewhat blurred.

Imagery Intelligence

Imagery intelligence (IMINT) has always been the aircraft’s forte. Imagery has traditionally involved photography, and although photographic imagery remains an important tool, technology has added additional tools to the IMINT toolbox. Infrared, electro-optic video, and radar also produce images that can provide valuable intelligence and see things that conventional photography cannot.

The aerial photograph provides a powerful intelligence tool. It freezes in time an image that can be minutely examined. The exact make and model of enemy equipment, the strength and deployment of enemy forces, the condition of roads and other lines of communication, the output of industrial plants, and the effectiveness of prior attacks can all be determined through aerial photography.

Photographic intelligence does have weaknesses, however. It cannot be gathered through obstructions such as clouds or smoke. It freezes a single instant in time, allowing detailed analysis, but may miss something that happened an instant before or after, and it may lack the context of a moving image.

There are three forms of aerial photographic image: the vertical, the oblique, and the panoramic. The vertical image is taken from directly over the target. It provides a constant scale, which can be determined from the focal length of the camera and altitude of the platform. It is the preferred format, but because it requires the camera platform to fly directly over the target, it can be a bit too dangerous in a high-threat environment.

An oblique image is taken at an angle from the target. It covers a good deal of ground and is much safer to take. While it gives definition to tall objects, such as radio aerials, it also allows terrain to mask possible targets. Because it does not provide a constant scale, measurements taken from it are far less precise. In addition, only the first one-third of the image is generally usable, whereas the rest of the image is captured at too flat an angle for any meaningful interpretation.

The panoramic image is a combination of the vertical and oblique images. It covers a vast area below the platform and off to both sides and combines the strengths and weaknesses of vertical and oblique.

Infrared Imagery

Infrared imagery (IR) provides an effective and deadly addition to the aerial reconnaissance toolbox. IR sees electromagnetic radiation at a wavelength lower than visible light, which is radiation that is produced by heat.

IR works most effectively when the difference between the heat of the targets and the ambient temperature is high. IR is far less effective at high noon than it is at midnight. At night, the ambient temperature usually drops well below the heat of human bodies and vehicle engines. When the differential is high, hot targets appear as glowing objects on a dark background.

In the 1980’s, forward-looking infrared (FLIR) was widely deployed. FLIR provides cueing for other intelligence assets and also works as a lethal target-acquisition tool for attack helicopters and low-altitude fighter-bombers. FLIR operates in real time and can capture movement as well as heat. If a target is both hot and moving, it will be detected.

Although FLIR can see much that conventional photography cannot, it cannot see through anything that absorbs or dissipates radiated heat, such as thick fog, rain, or solid obstacles.


Side-looking airborne radar (SLAR) has greatly expanded the vision and range of the aerial observer. The resolution has been improved to the point where individual buildings, roads, woods, and even vehicles can be reliably located. Added to these advantages is SLAR’s ability to use Doppler measurements to determine which of the returns is currently moving. These moving target indicators (MTIs) mean that mass ground targets such as armored regiments can be picked out and targeted in real time.

The U.S. Air Force has invested in a new class of battlefield surveillance aircraft based on various forms of SLAR. The mission of the joint surveillance target attack radar system (Joint STARS) is to fly parallel to the front line and look deep into the enemy’s rear for large-scale enemy movements and targets of opportunity. When teamed with the airborne warning and control system (AWACS), which uses radar to watch the skies deep into the enemy’s rear, the U.S. Air Force sees the battlefield in three dimensions, making it extremely difficult for any conventional modern army to operate without being under constant attack by aircraft, long-range artillery, and rockets.

Radar can see through darkness, fog, clouds, and all but the heaviest weather. It can also see through camouflage and any sort of obstacle that is not dense enough to stop radio waves. It also provides location information that is accurate enough for immediate targeting.

The weakness of radar is that it behaves in a way that is different enough from familiar visible light that its ability to identify targets is very limited. The shape of a radar return can vary according to the angle at which it strikes a target. Although much effort has been expended toward making radar blips more descriptive, none so far has been reliable. Objects smaller than a B-52 can be identified no more precisely than as probable armored vehicles or possible radars.

Signals Intelligence

In addition to imagery, aircraft make excellent platforms for devices that collect and analyze the signals from communications systems, radars, or other devices broadcasting electromagnetic radiation into the atmosphere. Signals intelligence (SIGINT) consists of communications intelligence (COMINT) that intercepts and locates radio communications and electronic intelligence (ELINT), which is the location and identification of non-communication emitters, primarily radars.

The Future

The turn of the twenty-first century has brought a revolutionary change in the nature of aerial reconnaissance. The reconnaissance pilot “alone, unarmed, and unafraid” has become increasingly rare. The future, and to a large degree, the present of aerial reconnaissance lies with the uninhabited aerial vehicle (UAV). Systems such as the U.S. Army’s Predator system are taking over the mission of battlefield reconnaissance. Using a combination of video and the Global Positioning System (GPS), they provide battlefield intelligence staffs with real-time intelligence information and accurate targeting without risking the lives of pilots.

The next stage of aerial reconnaissance is the replacement of many large radar and SIGINT platforms with long-endurance UAVs such as the Global Hawk. The long-range strategic mission will soon be performed by high-altitude uncrewed aircraft that will fly three times faster than the SR-71. These superfast UAVs, with their ability to fly on demand and address specific targets rather than follow fixed orbits, may eventually render the spy satellite obsolete.

New-generation UAVs carry sensors that will change the way imagery is collected and analyzed. Intelligence analysts will be able to interpret an image while the aircraft is still over the target, and advancements in digital image enhancement are making imagery even more useful. The future belongs to real-time sensors on a variety of aerial platforms (mostly uncrewed) networked to computerized command centers.

  • Stanley, Roy M. To Fool a Glass Eye: Camouflage Versus Photoreconnaissance in World War II. Washington, D.C.: Smithsonian Institution Press, 1998.
  • Vaughn, David, et al. Capturing the Essential Factors in Reconnaissance and Surveillance Force Sizing and Mix. Santa Monica, Calif.: RAND Project Air Force, 2000.



Fighter pilots

Military flight



Uncrewed spaceflight

Uninhabited aerial vehicles

World War I

World War II

The U-2 spy plane piloted by Francis Gary Powers was shot down over the Soviet Union on May 1, 1960, becoming one of the most notorious reconnaissance planes in history.

Categories: History