Kerrison Predictor - AbsoluteAstronomy.com

The Kerrison Predictor was one of the first fully automated anti-aircraft fire-control system

Fire-control system

A fire-control system is a number of components working together, usually a gun data computer, a director, and radar, which is designed to assist a weapon system in hitting its target. It performs the same task as a human gunner firing a weapon, but attempts to do so faster and more...

s. The predictor could aim a gun at an aircraft based on simple inputs like the observed speed and the angle to the target. Such devices had been used on ships for gunnery control for some time, and versions such as the Vickers Predictor

Vickers range clock

The Vickers Range Clock was a clockwork device used by the Royal Navy for continuously calculating the range to an enemy ship.In 1903, Percy Scott described a device he'd invented which was similar to the Vickers clock. In April 1904, Vickers worked with Scott and patented their device, samples of...

were available for larger anti-aircraft guns intended to be used against high-altitude bombers, but the Kerrison's electromechanical analog computer

Analog computer

An analog computer is a form of computer that uses the continuously-changeable aspects of physical phenomena such as electrical, mechanical, or hydraulic quantities to model the problem being solved...

was the first to be fast enough to be used in the demanding high-speed low-altitude role, which involved very short engagement times and high angular rates.

History

By the late 1930s, both Vickers

Vickers

Vickers was a famous name in British engineering that existed through many companies from 1828 until 1999.-Early history:Vickers was formed in Sheffield as a steel foundry by the miller Edward Vickers and his father-in-law George Naylor in 1828. Naylor was a partner in the foundry Naylor &...

and Sperry

Sperry

-Persons:*Armstrong Sperry , American author and illustrator*Brett Sperry , American video game designer*Carlos A. Sperry, Democratic President of the West Virginia Senate from Greenbrier County, served 1872-1872...

had developed predictors for use against high altitude bombers. However, low-flying aircraft presented a very different problem, with very short engagement times and high angular rates of motion, but at the same time less need for ballistic accuracy. Machine guns had been the preferred weapon of choice against these targets, aimed by eye and swung by hand, but these no longer had the performance needed to deal with the larger and faster aircraft of the 1930s.

The British Army

British Army

The British Army is the land warfare branch of Her Majesty's Armed Forces in the United Kingdom. It came into being with the unification of the Kingdom of England and Scotland into the Kingdom of Great Britain in 1707. The new British Army incorporated Regiments that had already existed in England...

's new Bofors 40 mm gun

Bofors 40 mm gun

The Bofors 40 mm gun is an anti-aircraft autocannon designed by the Swedish defence firm of Bofors Defence...

s were intended as their standard low-altitude anti-aircraft weapons. However, existing gunnery control systems were inadequate for the purpose; the range was too far to "guess" the lead, but at the same time close enough that the angle could change faster than the gunners could turn the traversal handles. Trying to operate a calculating gunsight at the same time was an added burden on the gunner. Making matters worse was that these ranges were exactly where the Luftwaffe
Luftwaffe
Luftwaffe is a generic German term for an air force. It is also the official name for two of the four historic German air forces, the Wehrmacht air arm founded in 1935 and disbanded in 1946; and the current Bundeswehr air arm founded in 1956....

s dive bomber

Dive bomber

A dive bomber is a bomber aircraft that dives directly at its targets in order to provide greater accuracy for the bomb it drops. Diving towards the target reduces the distance the bomb has to fall, which is the primary factor in determining the accuracy of the drop...

s were attacking from, which were quickly proving to be a decisive weapon in the Blitzkrieg
Blitzkrieg
For other uses of the word, see: Blitzkrieg Blitzkrieg is an anglicized word describing all-motorised force concentration of tanks, infantry, artillery, combat engineers and air power, concentrating overwhelming force at high speed to break through enemy lines, and, once the lines are broken,...

.

The Kerrison Predictor was a relatively simple device compared to high-altitude predictors, and was designed to meet these particular requirements. It was designed by Major A.V. Kerrison at the Admiralty Research Laboratory

Admiralty Research Laboratory

The Admiralty Research Laboratory, or ARL, was a research laboratory that supported the work of the UK Admiralty in Teddington, London, England....

, Teddington

Teddington

Teddington is a suburban area in the London Borough of Richmond upon Thames in south west London, on the north bank of the River Thames, between Hampton Wick and Twickenham. It stretches inland from the River Thames to Bushy Park...

, in the late 1930s. After the war, Kerrison went on to become Director of Aeronautical and Engineering Research at the British Admiralty.

The Predictor solved the problem by doing all of the calculations mechanically through a complex system of gears. Inputs to its calculations included wind speed, gravity, ballistics

Ballistics

Ballistics is the science of mechanics that deals with the flight, behavior, and effects of projectiles, especially bullets, gravity bombs, rockets, or the like; the science or art of designing and accelerating projectiles so as to achieve a desired performance.A ballistic body is a body which is...

of the gun and the rounds it fired, angle to the target in azimuth and altitude

Altitude

Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...

, and a user-input estimated target speed. Some of these inputs were fed in via dials, which turned gearing inside the Predictor to calculate the range (from the change in angle and estimated speed) and direction of motion. The "output" of the device drove hydraulic servo-motors attached to the traversal and elevation gears of the otherwise unmodified Bofors gun, allowing it to follow the predictor's indications automatically without manual intervention. The gunners simply kept the gun loaded, while the three aimers simply had to point the Predictor, mounted on a large tripod

Tripod

A tripod is a portable three-legged frame, used as a platform for supporting the weight and maintaining the stability of some other object. The word comes from the Greek tripous, meaning "three feet". A tripod provides stability against downward forces, horizontal forces and moments about the...

, at the target. The Kerrison predictor did not calculate fuse settings, as the shells fired by the 40 mm Bofors gun, with which it was designed to work, were contact fused.

The Predictor proved to be able to hit practically anything that flew in a straight line, and it was particularly effective against dive bombers. However, it was also very complex, including over 1,000 precision parts and weighing over 500 lb (226.8 kg), even though much of it was made of aluminum to reduce weight. With the demands of the RAF

Royal Air Force

The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...

for almost all light metals and machinists, the Predictor was far too difficult for the Army to produce in any quantity.

While the Predictor proved to be an excellent addition to the Bofors, it was not without its faults. The main problem was that the system required a fairly large electrical generator in order to drive the gun, increasing the logistics

Logistics

Logistics is the management of the flow of goods between the point of origin and the point of destination in order to meet the requirements of customers or corporations. Logistics involves the integration of information, transportation, inventory, warehousing, material handling, and packaging, and...

load in supplying the generators with fuel. Setting the system up was also a fairly complex task, and not something that could be done "on the fly". In the end they were used almost entirely for static emplacements, field units continuing to rely on their original iron sights or the simple Stiffkey-Stick sights that were introduced in late 1943.

The No.7 anti-aircraft composite predictor, also designed by Kerrison was similar in some ways. It was originally developed for the 6-pounder naval gun, for close-in defence and also against targets at intermediate altitudes of 6000 to 14000 ft (1,828.8 to 4,267.2 m). It was later adapted for use with the 40 mm Bofors.

US service

Because the U.S. Army Coast Artillery Corps

U.S. Army Coast Artillery Corps

The U.S. Army Coast Artillery Corps was a Corps level organization responsible for coastal and harbor defense of the United States between 1901 and 1950.-History:...

was not satisfied with the Army's 37mm Gun M1

37mm Gun M1

The 37mm Gun M1 was an anti-aircraft autocannon developed in the United States. It was used by the US Army in World War II.In addition to the towed variant, the gun was mounted, with two M2 machine guns, on the M2/M3 half-track, resulting in the T28/T28E1/M15/M15A1 series of multiple gun motor...

, in September 1940 General George C. Marshall

George Marshall

George Catlett Marshall was an American military leader, Chief of Staff of the Army, Secretary of State, and the third Secretary of Defense...

asked the British for the loan of four Bofors 40 mm guns with Kerrison Predictors for testing.

During testing the Kerrison Predictor provided accurate fire control to a range in excess of 1500 m (4,921.3 ft), and the Bofors gun was reliable, and in fall 1940, the Ordnance Department standardized the Kerrison Predictor for use with the 37 mm gun. By February 1941, the U.S. Navy had adopted the Bofors for use on their ships. To ease production problems, the Army reluctantly standardized on the 40 mm in February 1941; the U.S. was building the Bofors for the British under the Lend-Lease

Lend-Lease

Lend-Lease was the program under which the United States of America supplied the United Kingdom, the Soviet Union, China, Free France, and other Allied nations with materiel between 1941 and 1945. It was signed into law on March 11, 1941, a year and a half after the outbreak of war in Europe in...

Program.

The Predictor's plans were passed to Sperry

Sperry

, who were just commencing production of their own complex high-altitude system, the M7 Computing Sight, and had no excess capacity to produce the new design as well. Instead, they completed changes needed to U.S. production and sent the plans back to the Army for production elsewhere and in December 1940 the Singer Corporation

Singer Corporation

Singer Corporation is a manufacturer of sewing machines, first established as I.M. Singer & Co. in 1851 by Isaac Merritt Singer with New York lawyer Edward Clark. Best known for its sewing machines, it was renamed Singer Manufacturing Company in 1865, then The Singer Company in 1963. It is...

was contracted to produce 1,500 predictors per month to equip the Army's existing 37 mm guns while production of the 40 mm Bofors was ramped up. Singer required massive changes in the company, including building new factories and the switching of a foundry from steel to aluminum and production did not begin until January 1943, but the entire order was filled for the M5 Antiaircraft Director by the middle of 1944. For a brief time, some of the U.S. Army's Bofors guns were equipped with the Sperry M7, but these were replaced in the field as soon as M5s became available.

With aircraft speeds increasing dramatically during the war, even the speed of the Kerrison Predictor proved lacking by the end. Nevertheless, the Predictor demonstrated that effective gunnery required some sort of reasonably powerful computing support, and in 1944 Bell Labs

Bell Labs

Bell Laboratories is the research and development subsidiary of the French-owned Alcatel-Lucent and previously of the American Telephone & Telegraph Company , half-owned through its Western Electric manufacturing subsidiary.Bell Laboratories operates its...

started delivery of a new system based around an analog computer

Analog computer

. The timing proved excellent. Late in the summer the Germans started attacking London

London

London is the capital city of :England and the :United Kingdom, the largest metropolitan area in the United Kingdom, and the largest urban zone in the European Union by most measures. Located on the River Thames, London has been a major settlement for two millennia, its history going back to its...

with the V-1 flying bomb

V-1 flying bomb

The V-1 flying bomb, also known as the Buzz Bomb or Doodlebug, was an early pulse-jet-powered predecessor of the cruise missile....

, which flew at high speeds at low altitudes. After a month of limited success against them, every available anti-aircraft gun was moved to the strip of land on the approach to London, and the new sights proved to be more than capable against them. Daytime attacks were soon abandoned.

Long after the war, U.S. M5's started appearing in surplus shops in the late 1950s. John Whitney

John Whitney (animator)

John Whitney, Sr. was an American animator, composer and inventor, widely considered to be one of the fathers of computer animation.-Life:...

purchased one (and later a Sperry M7) and connected the electrical outputs to servo

Servomechanism

thumb|right|200px|Industrial servomotorThe grey/green cylinder is the [[Brush |brush-type]] [[DC motor]]. The black section at the bottom contains the [[Epicyclic gearing|planetary]] [[Reduction drive|reduction gear]], and the black object on top of the motor is the optical [[rotary encoder]] for...

s controlling the positioning of small lit targets and light bulbs. He then modified the "mathematics" of the system to move the targets in various mathematically controlled ways, a technique he referred to as incremental drift. As the power of the systems grew they eventually evolved into what is today known as motion control photography

Motion control photography

Motion control photography is a technique used in still and motion photography that enables precise control of, and optionally also allows repetition of, camera movements. It can be used to facilitate special effects photography. The process can involve filming several elements using the same...

, a widely used technique in special effects filming.

External links

Memories of Frank Yates
http://home.roadrunner.com/~featherweight/m5direct.htm
http://web.mit.edu/STS.035/www/PDFs/sperry.pdf

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

History

US service

See also

External links