Douglas A/B-26 Invader

The Norden bomb sight

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The Norden M-1 Bomb-Sight

Although the Norden bomb-sight was superior to other bombsights, it was not the first. Elmer Sperry, who had invented the gyroscopic compass, had developed the Sperry Gyroscope bombsight for the U.S. Army Air Force. Carl Norden had worked for the Sperry Gyroscope Company before developing the Norden bombsight.

The Sperry S-1 precision bomb-sight was developed in the 1930s. It was designated as "standard" equipment in March 1941 and was used in some US Army Air Force bombers early in WW II. However, all contracts for production of the Sperry sight were ordered cancelled in late 1943. Use of the better known Norden M-1 bomb-sight, invented by a naturalised Dutchman named Carl L. Norden, continued throughout the war.

The Norden bomb-sight was one of the most important U.S. military secrets of WW II. It was so advanced that crew members had to take an oath to protect its secrecy with their lives. It was a mechanical analog computer used to determine the exact moment bombs had to be dropped to accurately hit the target. The Norden bomb-sight provided the technical expertise needed to increase accuracy and make daylight strategic bombing possible. When properly aimed, it could place a bomb inside a 100 foot (31.4 meters) circle from four miles high (6436 meters).

Designed and developed for U.S. Naval aircraft by engineer Carl L. Norden, the bomb-sight was a complicated, 50 pound (23 kilos) piece of machinery, made up of gyros, motors, gears, mirrors, levers and a telescope containing some 2000 precision parts. The bombardier's job was to feed the computer the information it needed-air speed, wind speed, wind direction, altitude, and angle of drift. As the aircraft approached the target, the pilot turned the aircraft over to the bombardier and his bomb-sight. The bomb-sight was also an automatic pilot, and it flew the aircraft and released the bombs over the target. It would even compensate for the random pitch and roll of an aircraft during a bomb run.

Prior to the Manhattan Project, it was America's most secret weapon. Through cross-hairs made of spider's webbing, the Norden bomb-sight determined, with precision, the exact moment bombs were to be released to reach their target. At heart, the sight was a mechanical analog computer, not even as powerful as a pocket calculator today.

Programmed by the bombardier, the sight compensated for such factors as wind and drift. It was coupled with the autopilot to fly the bomber to the target, at which point it released the bombs.

It was often said that with the Norden bomb-sight, bombardiers could drop a bomb into a pickle barrel from 20,000 feet (6,096 meters). In reality, the sight's precision wasn't quite that dramatic. When testing the bomb-sight, half of the bombs dropped landed within 75 feet (23 meters) of the target. In actual wartime conditions of industrial haze, cloud coverage, and having to fly higher to evade enemy flak, the accuracy of the sight was considerably challenged.

Prior to a run, the bombardier checked the sight out of its guarded area, and mounted it in the plane. He connected the equipment and energised the gyros. He programmed the bomb's actual time of fall, and its trail.

Crouched in the Plexiglas nose of the plane and breathing pure oxygen, the bombardier set the target under the horizontal cross-hair of the sight. He had to wear silk gloves to keep his skin from freezing to the metal on the sight, due to temperatures well below freezing. As the craft withstood heavy flak and attacks from fighters, the sight compensated for crosswind, and the bombardier felt the weight of the mission on his shoulders.

Should his plane be shot down, he was responsible for destroying the bomb-sight in order to save its secret. Initially this was done by firing his pistol into the bomb-sight.

Considered a work in progress, numerous versions of the sight were created. By the end of the war, nearly 90,000 bomb-sights had been made.

On August 6th, 1945, bombardier Major Thomas Ferebee used a Norden bombsight to drop the uranium bomb, Little Boy, from the B-29 Enola Gay, 31,000 feet (9,449 meters) above Hiroshima.

Norden Bomb-sight Quick Facts

The bomb-sight has two main parts, the sighthead & the stabiliser. The stabiliser is rigidly mounted to the aircraft & contains a gyro spinning at 7,800 RPM, to provide yaw stability. The removable sighthead contains a gyro for roll & pitch stability, a motorised optical system for dropping & sighting angle, & an electrical trigger for bomb release. The bomb-sight flies the aircraft thorough the autopilot system during the final run.

Inventor: Carl L. Norden, contracted by the Navy's Bureau of ordnance in 1920.

Weight:50 pounds (23 kilos).

Cost: Carl L. Norden, Inc. charged $8,000 (in 1940's dollars) per sight during the war.

Trivia: On the 6th of August 1945, the bomb-sight teamed up with America's second secret weapon, in the atomic bombing of Hiroshima.

Hoosier Connection: 14,000 bomb-sights were produced at the Lukas-Harold Co. of Indianapolis, Indiana by 1945.

In 1943 the Norden M-series was delivered to the USAAF. It is estimated that this version was 6 to 8 times more precise than the Mk XIV bomb-sight used by the Royal Air Force. It is estimated that the RAF was capable of putting only 5% of its ordinance within a mile (1.61 km) of their aiming point under combat conditions. In contrast, the 8th Air Force was believed to be able to put 24% of their bombs to within 1,000 yds (914.4 m) of their targets. By 1944 this figure would rise to 40% to within 500 yds (457.2 m). The Norden bomb-sight enabled Allied bombers to fly above the flak and still hit their target with reasonable accuracy in clear weather. The daylight bombing strategy became a viable option to take the war to Germany and bring the war to a quick end.

When the Second World War broke out in Europe in 1939, air forces bombed from altitudes below 12,000 feet (3,658 meters) where crews did not require oxygen & aero engines did not need supercharging. The Americans planned to operate at more than twice this height. They equipped their heavy bombers with self-regulating oxygen systems for the crews. Their aircraft had turbo-supercharged engines & the very advanced Norden bomb-sight to obtain accurate bomb delivery. For the Norden to be effective however, the bombers needed to operate in clear skies. These are less common in Northern Europe than in the U.S. & the 8th came to rely on 'blind bombing' radar developed by the British.





Karl Lucas Norden

Karl Lucas Norden was born on April 23rd, 1880 in Semerang, Java,(now Indonesia) the third of five children. Following the death of his father in 1885, the family returned to Holland, then moved to Dresden, Germany in 1893. In 1896 he began a three year apprenticeship in a Swiss machine shop, after which he entered the world-famous Zürich Federal Polytechnic School. He graduated as a mechanical engineer in 1904 and went to America.

Norden worked for two years for the Worthington Pump and Machine Company in Brooklyn and from 1906 to 1911 at the J. H. Lidgerwood Manufacturing Company before moving to the Sperry Gyroscope Company. Elmer Sperry hired Norden to help design the first gyrostabilizer for large ships produced in the United States. While at Sperry, Norden married, and brought to America, Else Fehring who he had met years earlier in Zürich. In 1915, Norden left the Sperry company to set up his own business, but continued to work on Sperry's marine stabilizer contracts until 1917.

Norden won several patents on control systems for launching aerial torpedoes from ships. He also designed and furnished many instruments and devices for U.S. Navy bureaus, including robot flying bombs, radio-controlled target planes, and the catapults and arresting gear used on aircraft carriers. He also worked on a control system for aircraft, with others, which was a precursor of the automatic pilot.

In 1921, Norden began work on an instrument which could drop bombs from an aircraft and hit targets on land or sea. In 1923, Norden and Theodore H. Barth teamed up as partners and, over the next four years, Norden worked on the bombsight in Zürich while Barth assembled the parts in the US. In 1928, they incorporated their company as Carl L. Norden Incorporated with an order for two precision bombsights. Barth became the president and Norden took on the engineering work. In the first year the company developed a new bombsight with a timing mechanism to indicate the time to release the bomb.

In 1931, Norden demonstrated to the Navy a much improved bombsight in a test against the hulk of the heavy cruiser, Pittsburgh. Navy officials were so impressed by its accuracy they promptly ordered forty sights. The Army Air Corps also placed its own order.

The Air Corps, in 1935, installed Norden bombsights in Martin B-10s of the 7th and 19th Bomb Groups to develop the tactics of high-altitude, precision, daylight bombing. The first day of testing saw the B-10s coming within 520 feet of the targets from altitudes of 12,000 to 15,000 feet. By the end of the tests, the bombs were hitting within 164 feet of the targets.

Karl Norden died in 1965 & was enshrined in the National Aviation Hall of Fame in 1994.