H2S radar
Encyclopedia
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...
for the Royal Air Force
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...
and was used in various RAF bomber
Bomber
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:...
aircraft from 1943 to the 1990s. It was designed to identify targets on the ground for night and all-weather bombing. The early variants of the transmitter
Transmitter
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...
/receiver
Receiver (radio)
A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...
equipment were officially known as TR3159 (H2S Mk I/ASV VIB) or TR3191 (H2S Mk II).
On January 30, 1943, H2S radar was used by RAF bombers for navigation for the first time and so became the first ground mapping radar to be used in combat. Initially it was fitted to Stirling
Short Stirling
The Short Stirling was the first four-engined British heavy bomber of the Second World War. The Stirling was designed and built by Short Brothers to an Air Ministry specification from 1936, and entered service in 1941...
and Halifax
Handley Page Halifax
The Handley Page Halifax was one of the British front-line, four-engined heavy bombers of the Royal Air Force during the Second World War. A contemporary of the famous Avro Lancaster, the Halifax remained in service until the end of the war, performing a variety of duties in addition to bombing...
bombers and provided ground mapping for navigation and night bombing.
This development using ten-centimeter radar, (actually 9.1 cm) was possible thanks to the development of the cavity magnetron
Cavity magnetron
The cavity magnetron is a high-powered vacuum tube that generates microwaves using the interaction of a stream of electrons with a magnetic field. The 'resonant' cavity magnetron variant of the earlier magnetron tube was invented by John Randall and Harry Boot in 1940 at the University of...
. Later versions of H2S reduced the wavelength, first to 3 cm and then 1.5 cm at which wavelength the system was capable of detecting rain
Rain
Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...
clouds.
On a raid to Cologne
Bombing of Cologne in World War II
The City of Cologne was bombed in 262 separate air raids by the Allies during World War II, including 31 times by the Royal Air Force . Air raid alarms went off in the winter/spring of 1940 as enemy bombers passed overhead. However, the first actual bombing took place on 12 May 1940...
on 2/3 February 1943, a Stirling
Short Stirling
The Short Stirling was the first four-engined British heavy bomber of the Second World War. The Stirling was designed and built by Short Brothers to an Air Ministry specification from 1936, and entered service in 1941...
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...
was shot down over the Netherlands
Netherlands
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...
. The H2S set it was carrying was damaged but not beyond repair (fortunately for the Germans it was only the second operational use of H2S), and, known as the Rotterdam
Rotterdam
Rotterdam is the second-largest city in the Netherlands and one of the largest ports in the world. Starting as a dam on the Rotte river, Rotterdam has grown into a major international commercial centre...
Gerät, Telefunken
Telefunken
Telefunken is a German radio and television apparatus company, founded in Berlin in 1903, as a joint venture of Siemens & Halske and the Allgemeine Elektricitäts-Gesellschaft...
was able to reassemble it, with the exception of the PPI
Plan position indicator
The plan position indicator , is the most common type of radar display. The radar antenna is usually represented in the center of the display, so the distance from it and height above ground can be drawn as concentric circles...
display that had been destroyed. Eventually this led to the development of the Naxos radar detector
Naxos radar detector
The FuG 350 Naxos radar warning receiver was a World War II German countermeasure to SHF band centimetric wavelength radar produced by a cavity magnetron...
, which enabled 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....
night fighter
Night fighter
A night fighter is a fighter aircraft adapted for use at night or in other times of bad visibility...
s to home on the transmissions of H2S.
The United States later adapted the X-Band version of H2S (H2S Mk III) as the H2X radar
H2X radar
H2X radar was an American development of the British H2S radar, the first ground mapping radar to be used in combat. It was used by the USAAF during World War II as a navigation system for daylight overcast and nighttime operations...
which they regarded as a significant improvement. H2X was tested by RAF Bomber Command in 1945.
Second World War
After the Battle of BritainBattle of Britain
The Battle of Britain is the name given to the World War II air campaign waged by the German Air Force against the United Kingdom during the summer and autumn of 1940...
, RAF Bomber Command
RAF Bomber Command
RAF Bomber Command controlled the RAF's bomber forces from 1936 to 1968. During World War II the command destroyed a significant proportion of Nazi Germany's industries and many German cities, and in the 1960s stood at the peak of its postwar military power with the V bombers and a supplemental...
began night attacks against German cities. Although Bomber Command had reported good results from the raids, an independent analysis based on daylight air reconnaissance performed in the summer of 1940 showed that half the bombs fell on open country. Only one bomb in ten hit the target.
Radio electronics promised some improvement. The British developed a radio navigation system called "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....
" and then a second medium-range navigation scheme known as "Oboe
Oboe (navigation)
Oboe was a British aerial blind bombing targeting system in World War II, based on radio transponder 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...
". Gee and Oboe were limited in range to a line-of-sight
Line-of-sight propagation
Line-of-sight propagation refers to electro-magnetic radiation or acoustic wave propagation. Electromagnetic transmission includes light emissions traveling in a straight line...
to the transmitters.
A bomber carrying a night targeting system would not be limited in range to a UK-based transmitter. Taffy Bowen
Edward George Bowen
Edward George 'Taffy' Bowen, CBE, FRS was a British physicist who made a major contribution to the development of radar, and so helped win both the Battle of Britain and the Battle of the Atlantic...
had noticed during his early AI (Airborne Interception) experiments before the war that the radar returns from fields, cities and other areas were different. He had suggested development of targeting radar but the matter had been forgotten.
The idea resurfaced in 1941. Philip Dee
Philip Dee
Philip Ivor Dee was a British physicist. He was elected a Fellow of the Royal Society in 1941 and won its Hughes Medal in 1952...
's group had a 10 cm, 3 GHz AI flying in a Blenheim
Bristol Blenheim
The Bristol Blenheim was a British light bomber aircraft designed and built by the Bristol Aeroplane Company that was used extensively in the early days of the Second World War. It was adapted as an interim long-range and night fighter, pending the availability of the Beaufighter...
in March of that year. The experimental set was known as "AIS" in reference to its S-band operation. During tests of the AIS, Dee's team rediscovered that radar reflections could reveal different types of terrain.
In October 1941, Dee attended a meeting of the RAF Bomber Command where the night targeting issue was discussed. After the meeting on 1 November 1941, Dee performed an experiment in which he used an AIS radar mounted on a Blenheim to scan the ground. He was able to pick up the outline of a town 55 kilometres (34.2 mi) away.
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...
(TRE) set up a team under Bernard Lovell
Bernard Lovell
Sir Alfred Charles Bernard Lovell OBE, FRS is an English physicist and radio astronomer. He was the first Director of Jodrell Bank Observatory, from 1945 to 1980.-Early Life:...
(who later went on to become a leading figure in radio astronomy
Radio astronomy
Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The initial detection of radio waves from an astronomical object was made in the 1930s, when Karl Jansky observed radiation coming from the Milky Way. Subsequent observations have identified a number of...
) to develop an S-band airborne targeting radar based on AIS. The new targeting radar was designed to fit in an aerodynamic blister on the belly of a bomber, where the antenna would rotate to scan the terrain and feed the reflections to a Plan Position Indicator
Plan position indicator
The plan position indicator , is the most common type of radar display. The radar antenna is usually represented in the center of the display, so the distance from it and height above ground can be drawn as concentric circles...
display, producing a map of sorts of the land below the bomber.
The targeting radar was originally designated "BN (Blind Navigation)" but quickly became "H2S". The genesis of this designation remains somewhat mysterious, with different sources claiming it meant "Height to Slope"; or "Home Sweet Home". The "S" might have also had some connection to "S-band" but it is plausible the abbreviation was deliberately obscure as a security measure. There is also a rumour that it was named after hydrogen sulphide (chemical formula H2S, in connection with its rotten smell), because the inventor realised that had he simply pointed the radar downward instead of towards the sky, he would have a new use for radar, ground tracking instead of for identifying air targets and that it was simply 'rotten' that he hadn't thought of it sooner! The "rotten" connection, with a twist, is propounded by R V Jones
Reginald Victor Jones
Reginald Victor Jones, CH CB CBE FRS, was a British physicist and scientific military intelligence expert who played an important role in the defence of Britain in -Education:...
who relates the tale that, due to a misunderstanding between the original developers and Lord Cherwell
Frederick Lindemann, 1st Viscount Cherwell
Frederick Alexander Lindemann, 1st Viscount Cherwell FRS PC CH was an English physicist who was an influential scientific adviser to the British government, particularly Winston Churchill...
, development of the technology was delayed, the engineers thinking that Lord Cherwell wasn't keen on the idea. Later when Cherwell asked how the project was progressing he was most upset to hear that it had been put on hold and repeatedly declared about the delay that "it stinks". The engineers therefore christened the restarted project "H2S" and later, when Cherwell inquired as to what H2S stood, for no one dared tell Cherwell that it was named after his phrase—instead they pretended, on the spot, that it meant "Home Sweet Home"—which was the meaning that Cherwell related others (including R V Jones).
H2S performed its first experimental flight on 23 April 1942, with the radar mounted in a Halifax
Handley Page Halifax
The Handley Page Halifax was one of the British front-line, four-engined heavy bombers of the Royal Air Force during the Second World War. A contemporary of the famous Avro Lancaster, the Halifax remained in service until the end of the war, performing a variety of duties in addition to bombing...
bomber, the scanning unit installed in the aircraft's belly using the position previously occupied by the mid-under turret, which was by that time seldom installed. The scanning aerial
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
was covered by a distinctive streamlined radome
Radome
A radome is a structural, weatherproof enclosure that protects a microwave or radar antenna. The radome is constructed of material that minimally attenuates the electromagnetic signal transmitted or received by the antenna. In other words, the radome is transparent to radar or radio waves...
that was later to become a characteristic fitting of RAF heavy bombers. One problem was that to display as uniform a "map" of the terrain as possible, the radar effectively had to have low sensitivity or "gain" for targets directly underneath the bomber, with the gain increasing with target range. The scheme adopted was to tailor the power distribution in the aerial beam according to a cosecant-squared rule, so called after the mathematical function that defined the effective change in gain. The change in the beam was originally produced by fixing an angled metal plate on part of the parabolic reflector of the aerial, as may be seen in the picture of the aerial on a Halifax bomber. Later aerial reflectors were actually shaped with a cosecant-squared curvature.
Later the H2S scanner system would incorporate a gyro-stabilised mounting, reducing the effect of aircraft attitude in pitch and roll upon the reflected signal.
H2S was the TRE's priority and Lovell's team had use of the brilliant Alan Blumlein
Alan Blumlein
Alan Dower Blumlein was a British electronics engineer, notable for his many inventions in telecommunications, sound recording, stereo, television and radar...
and other top EMI
EMI
The EMI Group, also known as EMI Music or simply EMI, is a multinational music company headquartered in London, United Kingdom. It is the fourth-largest business group and family of record labels in the recording industry and one of the "big four" record companies. EMI Group also has a major...
engineers but there were snags. Intelligence reports had revealed the Germans had stationed a company of paratroopers near Cherbourg across the English Channel
English Channel
The English Channel , often referred to simply as the Channel, is an arm of the Atlantic Ocean that separates southern England from northern France, and joins the North Sea to the Atlantic. It is about long and varies in width from at its widest to in the Strait of Dover...
, suggesting the enemy might be planning to raid TRE, (just as the British had raided the French coast to seize a German Würzburg radar
Würzburg radar
The Würzburg radar was the primary ground-based gun laying radar for both the Luftwaffe and the German Army during World War II. Initial development took place before the war, entering service in 1940. Eventually over 4,000 Würzburgs of various models were produced...
in Operation Biting
Operation Biting
Operation Biting, also known as the Bruneval Raid, was the codename given to a British Combined Operations raid on a German radar installation in Bruneval, France that occurred between 27–28 February 1942 during World War II...
). On 25 May, the organization moved from Swanage
Swanage
Swanage is a coastal town and civil parish in the south east of Dorset, England. It is situated at the eastern end of the Isle of Purbeck, approximately 10 km south of Poole and 40 km east of Dorchester. The parish has a population of 10,124 . Nearby are Ballard Down and Old Harry Rocks,...
to Malvern College
Malvern College
Malvern College is a coeducational independent school located on a 250 acre campus near the town centre of Malvern, Worcestershire in England. Founded on 25 January 1865, until 1992, the College was a secondary school for boys aged 13 to 18...
, about 160 kilometres (99.4 mi) to the north.
Alan Blumlein
Alan Dower Blumlein was a British electronics engineer, notable for his many inventions in telecommunications, sound recording, stereo, television and radar...
and his loss was a huge blow to the program.
Churchill's science advisor Lord Cherwell wanted the design team to build H2S around the klystron
Klystron
A klystron is a specialized linear-beam vacuum tube . Klystrons are used as amplifiers at microwave and radio frequencies to produce both low-power reference signals for superheterodyne radar receivers and to produce high-power carrier waves for communications and the driving force for modern...
rather than the magnetron, not wanting to risk the secret of the magnetron falling into German hands. Once the Germans understood it they could quickly develop countermeasures against it. The klystron wasn't as powerful as the magnetron but it could be much more easily destroyed in an emergency. A magnetron's copper anode block, containing resonant cavities from which the operation of the device could be deduced, could survive large demolition charges.
The H2S design team did not believe the klystron could do the job and tests of an H2S built with klystrons instead of the cavity magnetron showed a drop in output power by a factor of 20 to 30. The H2S team also protested that it would take the Germans two years to develop a centimetric radar once the cavity magnetron fell into their hands and that there was no reason to believe they weren't working on the technology already. The first concern would prove correct; the second would be proven wrong, though given the widespread parallel development of the cavity magnetron, in hindsight it was not an unreasonable assumption.
Despite all the problems, on 3 July 1942 Churchill held a meeting with his military commanders and the H2S group, where he surprised the radar designers by demanding the delivery of 200 H2S sets by 15 October 1942. Bomber Command had to have H2S. The H2S design team was under great pressure but they were given priority on resources. The pressure also gave them an excellent argument to convince Lord Cherwell that the klystron-based H2S program be finally dropped.
It is perhaps interesting to note that the development of the in service radar sets was so rapid that the developers were forced to use existing plug and socket designs to connect the various units of the complete set together. There were no bulkhead mounting male connectors available at this time and consequently many of the male free connectors at the ends of cable runs carried exposed lethal voltages.
Despite extraordinary efforts TRE failed to meet the 15 October deadline. By 1 January 1943, twelve Stirling and twelve Halifax bombers had been fitted with H2S. On the night of 30 January 1943, thirteen "Pathfinder" bombers
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...
, which dropped incendiaries or flares on a target to "mark" it for other bombers following in the bomber "stream", took off to give H2S its introduction to combat by marking the German city of Hamburg
Hamburg
-History:The first historic name for the city was, according to Claudius Ptolemy's reports, Treva.But the city takes its modern name, Hamburg, from the first permanent building on the site, a castle whose construction was ordered by the Emperor Charlemagne in AD 808...
. Seven of the Pathfinders had to turn back but six marked the target, which was hit by a hundred Lancasters.
Bomber Command didn't use H2S generally until that summer. On the night of 24 July 1943, the RAF began Operation Gomorrah, a large attack on Hamburg. At that time, H2S was also fitted to Lancasters, which became a backbone of RAF Bomber Command. With the target marked by Pathfinders using H2S, RAF bombers hit the city with high explosive and incendiary bombs. They returned on the 25th and the 27th, with the USAAF
United States Army Air Forces
The United States Army Air Forces was the military aviation arm of the United States of America during and immediately after World War II, and the direct predecessor of the United States Air Force....
performing two daylight attacks in between the three RAF raids. Large parts of the city were burned to the ground by a cyclone of fire
Firestorm
A firestorm is a conflagration which attains such intensity that it creates and sustains its own wind system. It is most commonly a natural phenomenon, created during some of the largest bushfires, forest fires, and wildfires...
. About 45,000 people, mostly civilians, were killed.
H2S was vital in the air battle for Berlin
Battle of Berlin (air)
The Battle of Berlin was a British bombing campaign on Berlin from November 1943 – March 1944. The campaign was not limited solely to Berlin. Other German cities were attacked to prevent concentration of defences in Berlin, and Bomber Command had other responsibilities and operations to conduct...
, a series of large raids on the German capital and other cities from November 1943 until March 1944. Berlin was out of range of radio navigation aids such as Gee and Oboe and often obscured by cloud in the winter, so at the start of the battle it was hoped that H2S would, by identifying the many lakes and rivers in the city, be a crucial aid to navigation. The H2S sets available at the start of the battle were not able to do so. It was not until after the night of 2 December when the H2S Mark III, which operated on a 3 cm wavelength and could identify open and built up spaces, was successfully used for the first time on operations, that it became possible to bomb Berlin accurately.
Post-War
After the war, the RAF's Avro LincolnAvro Lincoln
The Avro Type 694, better known as the Avro Lincoln, was a British four-engined heavy bomber, which first flew on 9 June 1944. Developed from the Avro Lancaster, the first Lincoln variants were known initially as the Lancaster IV and V, but were renamed Lincoln I and II...
bombers were also equipped with H2S. In the 1950s, a later variant, H2S Mk.9, formed part of the Navigation and Bombing System (NBS) installed in the RAF's V-bomber force, comprising the Vickers Valiant
Vickers Valiant
The Vickers-Armstrongs Valiant was a British four-jet bomber, once part of the Royal Air Force's V bomber nuclear force in the 1950s and 1960s...
, Avro Vulcan
Avro Vulcan
The Avro Vulcan, sometimes referred to as the Hawker Siddeley Vulcan, was a jet-powered delta wing strategic bomber, operated by the Royal Air Force from 1956 until 1984. Aircraft manufacturer A V Roe & Co designed the Vulcan in response to Specification B.35/46. Of the three V bombers produced,...
and Handley Page Victor
Handley Page Victor
The Handley Page Victor was a British jet bomber aircraft produced by the Handley Page Aircraft Company during the Cold War. It was the third and final of the V-bombers that provided Britain's nuclear deterrent. The other two V-bombers were the Avro Vulcan and the Vickers Valiant. Some aircraft...
aircraft. Both the Vulcan and Victor participated in the 1982 Falklands War
Falklands War
The Falklands War , also called the Falklands Conflict or Falklands Crisis, was fought in 1982 between Argentina and the United Kingdom over the disputed Falkland Islands and South Georgia and the South Sandwich Islands...
, using their H2S radars to great effect, and the last of these aircraft were not withdrawn until 1993.
See also
- Naxos radar detectorNaxos radar detectorThe FuG 350 Naxos radar warning receiver was a World War II German countermeasure to SHF band centimetric wavelength radar produced by a cavity magnetron...
, created by Germany to spot H2S transmissions - List of World War II electronic warfare equipment
- FishpondFishpondFishpond was the code name given to an extension to the British H2S airborne radar system fitted to Royal Air Force Avro Lancaster and Handley Page Halifax heavy bombers during World War II...
External links
- Bournemouth University Radar Recollections site
- Picture of an installed H2S unit
- A working H2S Mk 9 and NBS as used in the Vulcan, Victor, and Valiant
- Bomber's Radar - General Survey of the Three Primary Systems Used by Bomber Command - FlightFlight InternationalFlight International is a global aerospace weekly publication produced in the UK. Founded in 1909, it is the world's oldest continuously published aviation news magazine...
article of September 1945