The Norden bombsight was a bombsight used by the United States Army Air Force during World War II, the Korean War, and the Vietnam War to aid the pilot of bomber aircraft in dropping bombs accurately. Its existence was a closely guarded secret of World War II.

Design and operation

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The Norden sight was originally designed for use on U.S. Navy aircraft by Carl Norden, a Dutch engineer educated in Switzerland who emigrated to the U.S. in 1904 and worked on bombsights at the Sperry Corporation. The Norden was built at the Air Force's Rome Laboratory in New York state. The device used a mechanical analog computer comprised of motors, gyros, mirrors, levels, gears, and a small telescope.

The bombardier would input the necessary information, such as airspeed and altitude, and the bombsight would calculate the trajectory of the bomb being dropped. Near the target the aircraft would fly on autopilot to the precise position calculated by the bombsight and release the ordnance. Using this device, bombardiers could, in theory, drop their bombs within a 100-foot (cca 30m) circle from an altitude of well over 20,000 feet (cca 7km). In combat, this accuracy was never achieved - because the Norden had been tested under "artificial conditions" at the US proving grounds, for example in the absence of anti-aircraft fire and/or adverse weather. An additional factor was that the shape and even the paint of the bomb mantle greatly changed the aerodynamic properties of the weapon; and the calculation of the trajectory of bombs that reached supersonic speeds during their fall was an unsolvable problem in those times.

Operational efficiency

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The "Norden" was marketed as the tool to win the war; and it was often touted that the bombsight would drop bombs in pickle barrels. As noted above, how effective the bombsight was is debated. Some argue that over typically cloud-covered Europe the Norden was nearly useless - which led the British Bomber Command to enter into indiscriminate aerial bombing during the night. However, the United States Army Air Forces (USAAF) did both day and night bombing runs depending on the distance, and many veteran B-17 and B-24 bombardiers swore by the Norden (not at it).

In the European theater, the US introduced an “AFCE” or “A. F. C. E.” Automatic Flight Control Equipment radar system called the H2X (Mickey) connected directly to the Norden bombsight. The AFCE served as the mechanical computer “autopilot” of the plane. This proved most accurate in coastal regions, as the water surface and the coastline produced a distinctive radar echo.

Over Japan, bomber crews soon discovered strong winds in high altitudes, the so-called jetstreams - but the Norden bombsight worked only for wind speeds with minimal wind shear under which testing had been done. Additionally, the bombing altitude over Japan reached up to 30,000 feet; but most of the testing has been done well below 20,000 ft.

In both theaters of war, one vunerability is that when the bombardier auto-piloted the airplane using the bombsight, the aircraft was more susceptible to anti-aircraft fire and collisions with other allied airplanes.

As a mechanical device, the Norden bombsight used complex machinery consisting of many gearwheels and ball bearings which were prone to produce inaccuracies if not properly maintained. In fact, many bombsights were rushed to war use without thorough testing; and often the bombardier had to oil and repair failures himself - for some time into the war equipped and qualified groundcrew technical staff were just not available in sufficient numbers (see below).

Wartime Security

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As a critical wartime instrument, bombardiers were required to take an oath during their training stating that they would defend the Norden secret with their own life if necessary. In case the bomber plane should make an emergency landing on enemy territory, the bombardier would have to shoot the important parts of the "Norden" with a gun, disabling it; but as this method still would leave a nearly intact apparatus to the enemy, something like a thermite gun was installed - the sheer heat of the chemical reaction would melt the "Norden" into a lump of metal.

After each completed mission, bomber crews left the airplane with a bag which they deposited in a safe ("the Bomb Vault"). This secure facilty ("the AFCE and Bombsight Shop") was typically in one of the base's Nissen hut support buildings. The Bombsight Shop was manned by enlisted men who were members of a Supply Depot Service Group ("Sub Depot") attached to each USAAF bombardment group. These shops not only guarded the bombsights but performed critical maintenance on the Norden and related control equipment. This was probably the most technically skilled ground echelon job, and certainly the most secret, of all the work performed by Sub Depot personnel. The non-commissioned officer in charge and his staff must have had a high aptitude for understanding and working with mechanical devices.

As the end of World War II neared, the bombsight was gradually downgraded in its secrecy; however, it was not until 1944 that the first public display of the instrument occurred.

Books

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• Stewart Halsey Ross: "Strategic Bombing by the United States in World War II"

features a chapter about the bombsights used by the USA. It describes the development, the fallacies, its use and how Germany soon learned about the Norden.

External links

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• Norden Bombsight from the Hill Aerospace Museum
• Last Combat Use
• U.S. Centennial of Flight Commission
• Additional images and detailed information

Air-dropped bombs | Cold War weapons of the United States | World War II military equipment of the United States