Oboe (navigation)
Oboe was a British
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 aerial blind bombing targeting system in World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

, based on radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...

In telecommunication, the term transponder has the following meanings:...

 technology. Oboe accurately measured the distance to an aircraft, and gave the pilot guidance on whether or not they were flying along a pre-selected circular route. The route was only 35 yards wide, allowing for much greater accuracy than competing systems like Gee
GEE (navigation)
Gee was the code name given to a radio navigation system used by the Royal Air Force during World War II.Different sources record the name as GEE or Gee. The naming supposedly comes from "Grid", so the lower case form is more correct, and is the form used in Drippy's publications. See Drippy 1946....

. The curved path Oboe-equipped aircraft followed was quite evident to German radar operators, who came to call the system "Boomerang" after the arc segment left on their displays as the aircraft appeared and disappeared out of range.

The system was first used in December 1941, about the same time as H2S radar
H2S radar
H2S was the first airborne, ground scanning radar system. It was developed in Britain in World War II for the Royal Air Force and was used in various RAF bomber aircraft from 1943 to the 1990s. It was designed to identify targets on the ground for night and all-weather bombing...

 was introduced and a few months after the first use of Gee. As it could only guide a single aircraft at a time, Oboe was used to guide the pathfinder
Pathfinder (RAF)
The Pathfinders were elite squadrons in RAF Bomber Command during World War II. They located and marked targets with flares, which a main bomber force could aim at, increasing the accuracy of their bombing...

 bombers to drop their target indicators for the initial stages of the raid; following bombers would use the markers as a reference for conventional bombsights. Gee, a passive system that could be used by an unlimited number of aircraft, remained in use for local guidance over the UK even after Oboe became widely used for bombing.

Technical details

Oboe used two stations at different and well-separated locations in England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

 to transmit
In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...

 a signal to a Mosquito
De Havilland Mosquito
The de Havilland DH.98 Mosquito was a British multi-role combat aircraft that served during the Second World War and the postwar era. It was known affectionately as the "Mossie" to its crews and was also nicknamed "The Wooden Wonder"...

Pathfinder (RAF)
The Pathfinders were elite squadrons in RAF Bomber Command during World War II. They located and marked targets with flares, which a main bomber force could aim at, increasing the accuracy of their bombing...

A bomber is a military aircraft designed to attack ground and sea targets, by dropping bombs on them, or – in recent years – by launching cruise missiles at them.-Classifications of bombers:...

 carrying a radio transponder. The transponder re-transmitted the signals, which were then received by the two stations. The round-trip time of each signal gave the distance to the bomber.

Each Oboe station used the radio ranging to define a circle of specific radius, with the intersection of the two circles pinpointing the target. The Mosquito flew along the circumference of the circle defined by one station, known as the "Cat
The cat , also known as the domestic cat or housecat to distinguish it from other felids and felines, is a small, usually furry, domesticated, carnivorous mammal that is valued by humans for its companionship and for its ability to hunt vermin and household pests...

", and dropped its load (either bombs, or marking flares, depending on the mission) when it reached the intersection with the circle defined by another station, known as "Mouse
A mouse is a small mammal belonging to the order of rodents. The best known mouse species is the common house mouse . It is also a popular pet. In some places, certain kinds of field mice are also common. This rodent is eaten by large birds such as hawks and eagles...

". There was a network of Oboe stations over southern England, and any of the stations could be operated as a Cat or a Mouse as the need demanded.

The initial "Mark I" Oboe was derived from Chain Home Low
Chain Home
Chain Home was the codename for the ring of coastal Early Warning radar stations built by the British before and during the Second World War. The system otherwise known as AMES Type 1 consisted of radar fixed on top of a radio tower mast, called a 'station' to provide long-range detection of...

 technology, operating at upper-range VHF frequencies of 1.5 meters / 200 MHz. The two stations emitted a series of pulses
Pulse (signal processing)
In signal processing, the term pulse has the following meanings:#A rapid, transient change in the amplitude of a signal from a baseline value to a higher or lower value, followed by a rapid return to the baseline value....

 at a rate of about 133 per second. The pulse width could be made short or long so it was received by the aircraft as a Morse code
Morse code
Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment...

 dot or dash. The Cat station sent continuous dots if the aircraft was too close and continuous dashes if the aircraft was too far, and from these the pilot could make the needed course corrections. (The Germans used a similar method with Knickebein.)

Various Morse letters could also be sent, for example to notify the aircraft crew that the Mosquito was within a specific range of the target. The Mouse station sent five dots and a dash to indicate bomb release. The Mouse station included a bombsight computer, known as "Micestro", to determine the proper release time, there being no particular logic in carrying the bombsight on the Mosquito when it was under the control of the ground station.

Although Oboe had been tested against Essen in January 1943, Oboe was rarely used for "big industrial plants" such as those in the Ruhr Area
Ruhr Area
The Ruhr, by German-speaking geographers and historians more accurately called Ruhr district or Ruhr region , is an urban area in North Rhine-Westphalia, Germany. With 4435 km² and a population of some 5.2 million , it is the largest urban agglomeration in Germany...

. The basic idea of Oboe was dreamt up by Alec Reeves
Alec Reeves
Alec Harley Reeves, CBE was a British scientist best known for his invention of pulse-code modulation . He was awarded 82 patents.-Early life:...

 of Standard Telephones and Cables
Standard Telephones and Cables
Standard Telephones and Cables Ltd was a British telephone, telegraph, radio, telecommunications and related equipment R&D manufacturer. During its history STC invented and developed several groundbreaking new technologies including PCM and optical fibres.The company began life in London as...

 Ltd, and implemented in a partnership with Frank Jones
Francis Jones (physicist)
Francis "Frank" Edgar Jones, FRS, MBE was a British physicist who co-developed the OBOE blind bombing system.He was born in Wolverhampton, the son of a teacher...

 of the TRE
Telecommunications Research Establishment
The Telecommunications Research Establishment was the main United Kingdom research and development organization for radio navigation, radar, infra-red detection for heat seeking missiles, and related work for the Royal Air Force during World War II and the years that followed. The name was...

 and had as part of the team Dr Denis Stops who later became a leading physicist at the University College London http://www.ucl.ac.uk. Denis Stops' role in the development of Oboe was so secret that he was drafted into the RAF Pathfinder Squadron as a Wing Commander to conduct his work. His role was largely to develop the systems on the aircraft in conjunction with the land based radar systems. The system worked by using triangulation
In trigonometry and geometry, triangulation is the process of determining the location of a point by measuring angles to it from known points at either end of a fixed baseline, rather than measuring distances to the point directly...

 to pin-point the target.

Operational history

Oboe was first used by Short Stirling heavy bombers in December 1941, attacking Brest
Brest, France
Brest is a city in the Finistère department in Brittany in northwestern France. Located in a sheltered position not far from the western tip of the Breton peninsula, and the western extremity of metropolitan France, Brest is an important harbour and the second French military port after Toulon...


In December 1942, Oboe on Mosquitos was trialled at Lutterade. Half of the Oboe units malfunctioned in some way. This was about the same time as H2S was introduced. The Germans, observing the curved path of the Mosquito, called the system "Boomerang". The predictable path of the bomber was a vulnerability, compensated for by the fact that the speed and 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...

 of the Mosquito made it very hard to intercept. The major limitation of Oboe was that it was a line-of-sight system; the curvature
In mathematics, curvature refers to any of a number of loosely related concepts in different areas of geometry. Intuitively, curvature is the amount by which a geometric object deviates from being flat, or straight in the case of a line, but this is defined in different ways depending on the context...

 of the Earth therefore allowed it to be useful for attacking the Ruhr industrial area
Ruhr Area
The Ruhr, by German-speaking geographers and historians more accurately called Ruhr district or Ruhr region , is an urban area in North Rhine-Westphalia, Germany. With 4435 km² and a population of some 5.2 million , it is the largest urban agglomeration in Germany...

, but not targets deeper inside Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...


Oboe was extremely accurate. In his book, Most Secret War, British physicist R. V. Jones wrote, "As it turned out, Oboe was the most precise bombing system of the whole war. It was so accurate that we had to look into the question of the geodetic alignment of the Ordnance Survey with the Continent, which effectively hinged on triangulation across the straits of Dover." With an error radius of about 110 meters (120 yards) at a range of 400 kilometres (248.5 mi), Oboe was about as good as optical bombsights. Late in the war it was used for humanitarian purposes to assist food drops to the Dutch
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...

 still trapped under German occupation, as part of Operation Manna. Drop points were arranged with Dutch Resistance
Resistance movement
A resistance movement is a group or collection of individual groups, dedicated to opposing an invader in an occupied country or the government of a sovereign state. It may seek to achieve its objects through either the use of nonviolent resistance or the use of armed force...

 contacts and the food canisters were dropped within about 30 m (100 ft) of the aiming point thanks to Oboe.

It took the Germans more than a year to discover the mystery of the system. Oboe was cracked by engineer H. Widdra (who had already detected the British "Pip Squeak" (IFF
Identification friend or foe
In telecommunications, identification, friend or foe is an identification system designed for command and control. It is a system that enables military and national interrogation systems to identify aircraft, vehicles, or forces as friendly and to determine their bearing and range from the...

) in 1940) at the end of August 1943 at the RF tracking station "Maibaum", located in Kettwig near Essen, while the British bombers attacked the steelworks of "Bochumer Verein".

The Germans tried to jam 1.5 metre / 200 MHz Oboe signals, though by the time they did the British had moved on to the 10 cm / 3 GHz
GHZ or GHz may refer to:# Gigahertz .# Greenberger-Horne-Zeilinger state — a quantum entanglement of three particles.# Galactic Habitable Zone — the region of a galaxy that is favorable to the formation of life....

 Mk.II Oboe and were using the old transmissions as a ruse. This was discovered in July 1944 after its operator failed to properly mark a drop using the Mk.1 signals.

The Mk.III of April 1944, was more sophisticated. Four aircraft could operate on one frequency and the system could accommodate approaches other than simple radial ones.

Similar systems

Interestingly, the Germans improvised a system conceptually similar to Oboe, code named Egon, to perform bombing on the Eastern Front
Eastern Front (World War II)
The Eastern Front of World War II was a theatre of World War II between the European Axis powers and co-belligerent Finland against the Soviet Union, Poland, and some other Allies which encompassed Northern, Southern and Eastern Europe from 22 June 1941 to 9 May 1945...

 on a limited scale. It used two modified Freya
Freya radar
Freya was an early warning radar deployed by Germany during World War II, named after the Norse Goddess Freyja. During the war over a thousand stations were built. A naval version operating on a slightly different wavelength was also developed as Seetakt...

s to play the roles of Cat and Mouse; these two Freya Egon sets were located about 150 km apart, and the aircraft carried a two channel IFF to respond to them. Voice radio directed the bombers. Despite the considerable effort the Germans put into other electronic navigation systems, they never took this concept farther.

Along with the range restriction, Oboe had another limitation: it could only really be used by one aircraft at a time. As a result, the British rethought Oboe, and came up with a new scheme named "GEE-H
G-H (navigation)
Gee-H, or sometimes G-H, was a radio navigation system developed by Britain during World War II to aid RAF Bomber Command. Its official name was AMES Type 100...

" (or "G-H") based on exactly the same thinking, differing only in having the aircraft carry the transmitter and fitting ground stations with the transponder.

Multiple aircraft could use the two stations in parallel because random noise was inserted into the timing of each aircraft's pulse output. The receiving gear on the aircraft could match its own unique pulse pattern with that sent back by the transponder. Each receive-reply cycle took the transponder 100 microsecond
A microsecond is an SI unit of time equal to one millionth of a second. Its symbol is µs.A microsecond is equal to 1000 nanoseconds or 1/1000 millisecond...

s, allowing it to handle a maximum of 10,000 interrogations per second and making "collisions" unlikely. The practical limit was about 80 aircraft at one time.

The name "GEE-H" is confusing, since the scheme was very close to Oboe and not very much like GEE
GEE (navigation)
Gee was the code name given to a radio navigation system used by the Royal Air Force during World War II.Different sources record the name as GEE or Gee. The naming supposedly comes from "Grid", so the lower case form is more correct, and is the form used in Drippy's publications. See Drippy 1946....

. The name was adopted because the system was based on GEE technologies, operating on the same range of 15 to 3.5 meters / 20 to 85 MHz, and initially used the GEE display and calibrator. The "H" suffix came from the system using the twin-range or 'H' principle of measuring the range from transponders at two ground stations. It was about as accurate as Oboe.

In popular culture

Oboe appears as a plot point in the "Lost Sheep" episode of the BBC
The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...

 television series Secret Army
Secret Army (TV series)
Secret Army is a television drama series made by the BBC and the Belgian national broadcaster BRT created by Gerard Glaister. The series chronicled the history of a Belgian resistance movement during the Second World War dedicated to returning Allied airmen, usually having been shot down by the...

, which featured the search for a downed airman with technical knowledge of the system.

External links

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