Norden bombsight

The Norden bombsight

A page from the Bombardier's Information File (BIF) that describes the components and controls of the Norden Bombsight.

Enola Gay bombardier Thomas Ferebee with the Norden Bombsight on Tinian after the dropping of Little Boy.

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 crew of bomber aircraft in dropping bombs accurately. Its operation was a closely guarded secret of World War II.

Design and operation

The Norden sight was designed for use on US Navy aircraft by Carl Norden, a Dutch engineer educated in Switzerland who emigrated to the US in 1904 and worked on bombsights at the Sperry Corporation before starting his own company. The Norden was initially built at the Norden plant in New York City before the start of WWII and then at several other companies during the war. The device used a mechanical analog computer comprising electric motors, gyros, mirrors, bubble 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 a precise position calculated by the bombsight and release the ordnance. Using this device, bombardiers could, in theory, drop their bombs within a 100-foot (ca 30m) circle from an altitude of well over 20,000 feet (ca. 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 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, at that time, nobody knew how to calculate the trajectory of bombs that reached supersonic speeds during their fall.

Under perfect conditions only 50 percent of American bombs fell within a quarter of a mile of the target, and American flyers estimated that as many as 90 percent of bombs could miss their targets. ^{[1] [2] [3]}

Operational efficiency

The "Norden" was marketed as the tool to win the war; and it was often claimed that the bombsight could drop bombs into pickle barrels. As noted above, the bombsight's effectiveness is debated. Some argue that over typically cloud-covered Europe the Norden was nearly useless, and the British Bomber Command focused on nighttime bombing anyway. 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.

In the European theater, the US introduced an Automatic Flight Control Equipment (AFCE) and a radar system called the H2X (Mickey), which were used directly with the Norden bombsight. The AFCE served as the mechanical computer “autopilot” of the plane. The radar 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 at 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 had been done well below 20,000 ft.

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

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. 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

Photo of the AFCE and Bombsight shop groundcrew in the 463rd Sub Depot affiliated with the USAAF 389th Bomb Group based at Hethel, Norfolk, England

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 aircraft with a bag which they deposited in a safe ("the Bomb Vault"). This secure facility ("the AFCE and Bombsight Shop") was typically in one of the base's Nissen hut (Quonset 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 had to have 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.

Its last use in combat was by the Naval Air Observation Squadron Sixty-Seven (VO-67), during the Vietnam War. The bombsights were used in Operation Igloo White for dropping Air-Delivered Seismic Intrusion Detectors (ADSID) along the Ho Chi Minh Trail.

Espionage

FBI file photo

Main article: Duquesne Spy Ring

Herman W. Lang, a German spy, had been employed by the Carl L. Norden Company. During a visit to Germany in 1938, Lang conferred with German military authorities and reconstructed plans of the confidential materials from memory. In 1941, Lang, along with the 32 other German agents of the Duquesne Spy Ring, was arrested by the FBI in the largest espionage conviction in U.S. History. He received a sentence of 18 years in prison on espionage charges and a 2-year concurrent sentence under the Foreign Agents Registration Act.

See also

• Stabilizing Automatic Bomb Sight (SABS) a Royal Air Force bomb sight introduced for precision bombing with similar capabilities to the Norden bomb sight.

References

This article incorporates text from http://foia.fbi.gov/foiaindex/duquesne_frederick_interesting.htm Federal Bureau of Investigation: Frederick Duquesne Interesting Case Write-up (publicly released on March 12, 1985 under the Freedom of Information Act), a public domain work of the United States Government. Accessed: 2007–05–12

Further reading

Books

• 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.
• Albert L. Pardini: "The Legendary Norden Bombsight"
  The first detailed volume to cover the Norden Bombsight. 352 pages with over 70 b/w photographs plus line art. ISBN 0-7643-0723-1, Schiffer Publishing, 1999.
• "The Norden Bombsight"
  A classified manual during WW II, this is a complete guide to maintenance and calibration of the Norden bombsight. 200+ pages.
• "Bombing – Students' Manual"
  This WW II bombardiers instruction book includes Norden bombsight instruction and more. 250+ pages, illustrated.
• "Bombardier's Information File"
  This manual features instructions for the use of the Norden Bombsight, and other bomb sights as well. Illustrated with photos of bombs, cameras, various equipment, etc.
• Loyd Searle: "The Bombsight War: Norden vs. Sperry"
  Gives many details of the history and behind-the-scenes development of the NBS and its competitor. Spectrum IEEE #0018-92235/89/0900-0060, September 1989, http://www.thevaluesell.com/images/LSearle_bombsight.pdf

Articles

• Norden Bombsight from the Hill Aerospace Museum
• Last Combat Use Observation Squadron Sixty-Seven ( VO-67 )
• U.S. Centennial of Flight Commission
• Additional images and detailed information
• WWII AAF collection (Bombardiers Information File)
• (Movies of the Norden and Sperry Bombsights in operation)

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