Norden bomb sighting device

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Norden bomb sighting device in an A-26 Invader

The Norden bomb sighting device was a bomb sighting device that was mainly used in American bombers during World War II . In its time it was considered the most precise target optics with which a strategic bomber had ever been equipped and was used in almost all horizontal bombers of the United States Army Air Forces , for example in the Boeing B-17 , the B-24 Liberator , and the North American B-25 , the A-26 Invader or the Boeing B-29 , but also in naval aircraft such as the Douglas TBD Devastator . It is named after its inventor Carl Lucas Norden .

history

Illustration from the user manual of the device
The Enola Gay bombardier, Thomas Ferebee, with his Norden aiming device

With a typical bomb sight from the time between the two world wars, the bombardier first had to enter some values, such as the wind speed or the ballistic properties of the bomb. Then he could see through a crosshair eyepiece the point where a dropped bomb would hit. The center of the crosshair thus constantly moved towards the target during the target approach. The bombardier communicated the necessary course corrections to the pilot by hand signals. When the center of the crosshair reached the target, the bombardier triggered the bombs. However, the accuracy of these aiming devices has been severely affected by the fact that, in practice, aircraft are rarely completely still in the air. Therefore, the first attempts were made with gyro-stabilized aiming devices, which were supposed to compensate for the aircraft's own movements.

When the aircraft became larger and the pilot no longer had the bombardier in view, the Pilot direction indicator (PDI) was developed, in which the bombardier operated a pointer instrument by means of an electrical switch , which was in the pilot's field of vision and indicated the necessary course corrections .

Norden improved this process by not only placing the target device on a gyro-stabilized platform - the signals for the course correction display were now automatically generated and transmitted to the pilot. In addition, the crosshairs no longer "wandered" over the target area towards the target, but instead the crosshairs remained constantly aimed at the target.

The first Norden Mark XI devices were handed over to the US Navy for testing purposes in 1924 . The results were disappointing - the accuracy left a lot to be desired and the device was very complicated to use. It was only when the hit probability had been significantly increased that the Navy placed its first order in 1928. In 1931 the United States Army Air Corps (USAAC) also acquired a copy and came to essentially the same results. In the meantime, Norden had developed the much improved Mark XV version, which was above all much easier to use. However, she still used the PDI to transmit the necessary course corrections to the pilot. Norden later developed the Stabilized Bombing Approach Equipment (SBAE) , a primitive autopilot that could be coupled directly to the Mark XV.

Despite all the improvements, the Mark XV still had weaknesses. For example, Norden used DC motors to drive his gyroscopes . The carbon brushes required for this wear out quickly, so they often had to be replaced and they also contaminated the mechanics with coal dust. Before the actual targets the device had to first by means of two dragonflies are leveled, which took eight and a half minutes. By turbulence or violent maneuvers , it could happen that the centrifugal lost their direction and leveling had to be repeated. The bomber also had to maintain altitude during the entire approach, which made it more vulnerable to enemy anti-aircraft guns .

Due to an exclusive contract between Norden and the US Navy, USAAC had to obtain all of its Norden bomb sights from the Navy. However, since this claimed the lion's share of all Norden devices produced for itself, the Army turned to the Sperry Corporation , which had developed a similar system with the S-1 (originally referred to as O-1). In contrast to the Norden device, the tops of the Sperry S-1 ran on alternating current, which is why the problems with the carbon brushes were eliminated; The speed of rotation of the gyroscope was 24,000 / min, more than three times as high as that of the Norden device with 7,800 / min. With the A-5, the counterpart to Nordens SBAE, Sperry also developed the world's first fully electronic autopilot.

The Army initially used its Norden bomb sighting devices primarily in its B17 bombers , while it initially equipped its B-24 Liberator with Sperry devices.

In June 1941, Sperry received an order from the US government to build a 186,000 square meter factory. The USAAC wanted to equip all of its bombers with type A-5 autopilots, which would then be paired with either a Norden bomb sighting device or a Sperry S-1. However, Norden refused to make his device compatible with the Sperry A-5. In January 1942, the Air Corps commissioned Honeywell to develop a new autopilot. This combined elements from Nordens SBAE and Sperrys A-5 to the so-called Automatic Flight Control Equipment (AFCE) , later called C-1.

In 1943, the Navy saw its need for Norden bomb sighting devices as being covered, also because, when fighting (moving) ships, instead of horizontal bombing, it was increasingly resorting to dive attacks . In the same year the Army canceled its contract with Sperry and from then on only bought Norden bomb sights. These could now be coupled directly to the Honeywell C-1 so that the bombardier could practically control the aircraft with his bomb aiming device when approaching the target.

In total, approximately 43,000 Norden Mark XV bomb sights were manufactured for the US military, including 35,000 for the USAAF and 8,000 for the Navy.

A special simulator, similar to the flight simulators for pilots , was developed in order to save costs in the training of budding bombers .

During the Korean War , some older types of aircraft with the Norden bomb sight, such as the B-29 Superfortress, were reactivated. The device was also used in isolated cases during the Vietnam War .

confidentiality

The existence and functioning of the Norden device was initially kept top secret. Budding bombardiers had to swear an oath to protect the secret with their lives if necessary. In the event of an emergency landing in enemy territory, or before parachuting, the bombardier should destroy the aiming device with three shots from a .45 ACP pistol or, even better, a thermite charge . It was not until April 1943 that the secrecy was lifted after a few copies of the device had already been captured by the Axis powers . However, at this point in time, essential information about the device had already been revealed to the Germans by the spy Herman W. Lang .

Discussion about the effectiveness of precision attacks

While the British flew their air strikes mainly at night and on area targets like entire cities, the Americans believed, thanks to the high accuracy of their bombers, that daytime attacks on point targets would be more successful in the long run. After all, with the Norden aiming device, you could "throw a bomb into a herring barrel from a height of 6000 meters". In addition, the stronger defensive armament of their bombers (compared to the British) would keep their own losses within limits. However, the British remained skeptical. In particular, Arthur Harris , the commander in chief of the RAF Bomber Command , criticized that the Norden bomb sighting device had so far only been tested under ideal conditions in the sunny, cloudless southwest of the USA. In Europe, on the other hand, visibility is often obscured by clouds, fog or smoke. Harris told the American war correspondent Allan Michie that in order to hit a barrel, you have to see it first. In fact, the hit rate in reality was significantly worse than the Americans expected. For example, in an attack on ball bearing factories in Schweinfurt in October 1943, only about 10% of the bombs dropped landed less than 500 feet (about 150 meters) from the target. In addition, the Americans initially suffered great losses, which only improved when long-range escort fighters such as the P-51 Mustang were available.

In Japan, too, the view of the earth was not always clear - for example, during the second atomic bombing on August 9, the primary target Kokura was covered by thick clouds, so that the Fat Man atomic bomb had to be dropped over Nagasaki instead .

Trivia

At a ceremony in Madison Square Garden to mark the presentation of the third Army-Navy "E" Award to the Carl L. Norden Company, the Ringling Bros. and Barnum & Bailey Circus performed a number referring to the accuracy of the Norden bomb sight in 1943 and alluded to the discussion with the barrels. With the help of a raised replica of the device, a clown dropped a wooden bomb into a barrel.

Web links

Commons : north bombsights  - collection of pictures, videos and audio files

Individual evidence

  1. ^ John Keegan : The Second World War , Rowohlt Verlag 2009, ISBN 978-3499619144 .
  2. ↑ Ingo Bauernfeind: Carrier aircraft of the Second World War: 1939-1945 , Motorbuch Verlag, Stuttgart 2014, ISBN 978-3613036628
  3. ^ Barrett Tillman: TBD Devastator Units of the US Navy , Osprey Publishing , London.
  4. ↑ a b c d e f g h i Loyd Searle: The bombsight war: North vs. Sperry , in: Spectrum IEEE , September 1989 (PDF)
  5. ^ Timothy Moy: War Machines: Transforming Technologies in the US Military, 1920-1940 , Texas A&M University Press
  6. ↑ Volta Torrey: The War's Most Closely Guarded Secret Revealed: How The Norden Bombsight Does Its Job , in: Popular Science , June 1945
  7. ↑ Picture of the week: Bombardier cadets swear to protect secrecy of US bombsight , in: LIFE , August 10, 1942
  8. ↑ Patrick Coffey: American Arsenal: A Century of A Century of Waging War , Oxford University Press , ISBN 978-0-19-995974-7
  9. ^ New York Bomb: Norden company takes over circus to see bomb hit pickle in barrel in: LIFE, April 26, 1943
  10. ↑ According to other sources, it was 25,000 feet , or about 7600 meters, see Ernest Haveman: Toughest Cop of the Western World , in: LIFE, June 14, 1954
  11. ↑ Ronald H. Bailey: The Air War in Europe , Time Life, ISBN 90-6182-432-X
  12. ↑ Oakland Aviation Museum: North Bombsight , accessed June 11, 2017
  13. ^ New York Bomb: Norden company takes over circus to see bomb hit pickle in barrel in: LIFE, April 26, 1943