An early H2S picture of the Pembroke and Milford Haven area

The H2S radar was used in bombers of RAF Bomber Command. It was designed to identify targets on the ground for night and all-weather bombing. Image File history File linksMetadata H2S_-_Pembroke_And_Milford_Haven. ... Image File history File linksMetadata H2S_-_Pembroke_And_Milford_Haven. ... Pembroke (Welsh: Penfro) is a town in west Wales. ... Milford Haven (Welsh: Aberdaugleddau meaning Mouth of the Two Cleddaus) is a town in Pembrokeshire, Wales. ... This long range radar antenna (approximately 40m (130ft) in diameter) rotates on a track to observe activities near the horizon. ... RAF Bomber Command was the organisation that controlled the RAFs bomber forces. ...

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 and Halifax bombers and provided a ground mapping capability for both navigation and night bombing. January 30 is the 30th day of the year in the Gregorian calendar. ... 1943 (MCMXLIII) is a common year starting on Friday. ... The Stirling was a World War II heavy bomber design built by Short Brothers. ... Halifax W1057 ZA-X of No. ...

This develoment, using ten-centimeter radar, (actually 9.1 cm) was possible thanks to the development of the cavity magnetron. Later versions of H2S reduced the wavelength used, first to 3 cm and then 1.5 cm, at which wavelength the system was capable of detecting rain clouds. A cavity magnetron is a high-powered vacuum tube that generates coherent microwaves. ... Rain falling For other uses see Rain (disambiguation). ...

Later in World War II the Luftwaffe night fighters used Naxos radar detectors to home in on the transmissions of H2S. Combatants Allied Powers Axis Powers Commanders {{{commander1}}} {{{commander2}}} Strength {{{strength1}}} {{{strength2}}} Casualties 17 million military deaths 7 million military deaths World War II, also known as the Second World War (sometimes WW2 or WWII), was a mid-20th century conflict that engulfed much of the globe and is accepted as... The Luftwaffe â–¶(?) (German: air force, IPA: [luftvafÉ™]) is the commonly used term for the German air force. ... A night fighter is a fighter aircraft adapted for use at night, or in other times of bad visibility. ... Naxos radar detector was a World War II German counter measure to centimetric radar produced by a cavity magnetron. ...

The Americans adapted the X-Band version of H2S (H2S Mk VI) as H2X radar which they regarded as a significant improvement and which was tested by the RAF Bomber Command in 1945. The X band ranges from 8. ... The H2X radar, nicknamed the Mickey set, provided a ground mapping capability for both navigation and in daylight when overcast (and at night) for the USAAF during World War II. The H2X system replaced the British H2S radar. ...

History

After the Battle of Britain, RAF Bomber Command began to ramp up night attacks against German cities. Unfortunately, although Bomber Command reported grand 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 actually hit the intended target. Combatants British Royal Air Force and allies Nazi German Luftwaffe Commanders Hugh Dowding Hermann Göring Strength approx 700 fighters (at the beginning) 1,260 bombers; 316 dive-bombers; 1,089 fighters Casualties 1,547 aircraft; Civilian: 27,450 dead, 32,138 wounded 1,887 aircraft A major campaign of... 1940 (MCMXL) was a leap year starting on Monday (link will take you to calendar). ...

Radio electronics promised some relief. The British developed a radio navigation system called "GEE", and then a second long range navigation scheme known as "Oboe". Gee and Oboe were limited in range to a line of sight to the transmitters. GEE (short for Grid and pronounced simply as G) or AMES Type 7000 was a British radio navigation system used during World War II; the ideas in GEE were developed by the Americans into the LORAN system. ... For the musical instrument of the woodwind family see Oboe Oboe was based on radio transponder technology. ...

A bomber carrying its own, self-contained night targeting system would not be limited in range to a UK-based transmitter. Taffy Bowen had noticed during his early AI experiments before the war that the radar returns from fields, cities, and other areas were distinctively different. He had suggested development of targeting radar, but the matter was forgotten in the chaos. Edward George Taffy Bowen CBE FRS (14 January 1911-12 August 1991) 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. ...

The idea resurfaced in 1941. Philip Dee's group had got a 10 cm / 3 GHz AI flying in a Blenheim 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. For the movie, see 1941 (film) 1941 (MCMXLI) was a common year starting on Wednesday (link will take you to calendar). ... The Bristol Type 142M Blenheim was a high-speed light bomber used extensively in the early days of World War II, built by Bristol Aeroplane Company. ...

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 kilometers (35 miles) away. November 1 is the 305th day of the year (306th in leap years) in the Gregorian Calendar, with 60 days remaining. ...

The H2S radome (top) and its enclosed scanning aerial (bottom) on a Halifax

The brass were impressed, and on the first day of 1942, the Telecommunications Research Establishment (TRE) set up a team under Bernard Lovell (who later went on to become a leading figure in radio astronomy) to develop an S-band airborne targeting radar, based on AIS. The new targeting radar was designed to fit in a blister on the belly of a bomber, where the antenna would rotate to scan the terrain and feed the reflections to a PPI display, producing a map of sorts of the land below the bomber. ImageMetadata File history File links Download high resolution version (400x618, 160 KB) The H2S radome (top) and the enclosed, rotating, scanning aerial (bottom) on a Handley Page Halifax. ... ImageMetadata File history File links Download high resolution version (400x618, 160 KB) The H2S radome (top) and the enclosed, rotating, scanning aerial (bottom) on a Handley Page Halifax. ... Radomes at the Cryptologic Operations Center, Misawa, Japan. ... A yagi antenna Most simply, an antenna (U.S.) or aerial (UK) is an electronic component designed to transmit or receive radio waves. ... This article is about the year. ... The Telecommunications Research Establishment (TRE) was established in Malvern, England in 1940 as the central research group for RAF applications of radar. ... Sir Bernard Lovell (born 1913) is a British radio astronomer, director (until 1981) of the Jodrell Bank Observatory. ... Microwave image of 3C353 galaxy at 8. ...

The targeting radar was originally designated "BN (Blind Navigation)", but quickly became "H2S". This acronym remains somewhat mysterious, with different sources claiming it meant "Height to Slope"; the smelly compound hydrogen sulfide, with the possible interpretation of "it stinks" (reputedly once used by Lord Cherwell to describe the device); or, with a little rearrangement, "Home Sweet Home". The "S" might have also had some connection to "S-band", but it is plausible the acronym was deliberately obscure and misleading as a security measure. There is also a rumour that it was named after this compound, because the inventor realised that had he simply pointed the radar DOWNWARD instead of towards the sky, he would have an entirely new application for radar, ground tracking instead of simply for identifying air targets, and that it was simply 'rotten' that he hadn't thought of it sooner! Hydrogen sulfide (hydrogen sulphide in British English), H2S, is a colorless, toxic, flammable gas that is responsible for the foul odor of rotten eggs. ... Professor Frederick Alexander Lindemann, 1st Viscount Cherwell (April 5, 1886 - July 3, 1957) was a physicist who became an influential scientific adviser to the British government and a close associate of Winston Churchill. ...

H2S performed its first experimental flight on 23 April, with the radar mounted in a Handley Page Halifax bomber. There was much still to be done. For example, in order to display as a uniform a "map" of the terrain as possible, the radar had to have low sensitivity or "gain" for targets directly underneath the bomber, with the gain increasing with the angle of the radar away from vertical. This scheme would become known as "cosecant-squared" scanning, after the mathematical function that defined the change in gain. April 23 is the 113th day of the year in the Gregorian Calendar (114th in leap years). ... Halifax W1057 ZA-X of No. ... In mathematics, the trigonometric functions are functions of an angle, important when studying triangles and modeling periodic phenomena. ...

H2S was the TRE's top priority, and Lovell's team had use of the brilliant Alan Blumlein and other top EMI engineers, but there were snags. Intelligence reports had revealed the Germans had stationed a company of paratroopers near Cherbourg, across the channel, suggesting the enemy might be planning to raid the TRE. On 25 May, the entire organization moved out in another mad, infuriating fire drill from Swanage to Malvern College, about 160 kilometers (100 miles) to the north. Fortunately, this would prove to be the last move. Alan Dower Blumlein was an electronics engineer who made a great many inventions in telecommunications, sound recording, stereo, television and radar. ... Cherbourg is a city of Normandy, in northwestern France, in the Manche département, of which it is a sous_préfecture. ... May 25 is the 145th day of the year in the Gregorian calendar (146th in leap years). ... Location within the British Isles Swanage station, the terminus of the Swanage heritage railway. ... Malvern College is a coeducational English public school for pupils aged 13 to 18, founded in 1865. ...

The Halifax V9977, which crashed in June 1942, killing several key radar technicians

As if this weren't bad enough, then an outright disaster occurred. On 7 June 1942, the Halifax performing H2S tests (right) crashed, killing everyone on board and destroying the prototype H2S. One of the dead was Alan Blumlein, and his loss was a major blow to the program. ImageMetadata File history File links Halifax_V9977. ... ImageMetadata File history File links Halifax_V9977. ... June 7 is the 158th day of the year in the Gregorian calendar (159th in leap years), with 207 days remaining. ... This article is about the year. ...

Furthermore, Churchill's science advisor Lord Cherwell wanted the design team to build H2S around the klystron rather than the magnetron. Cherwell was opinionated, obstinate, contrary, something like Churchill himself but without quite as many redeeming features. Most people who had to deal with Cherwell regarded him, with some justification, as an obstructionist who tried to create problems instead of figuring out how to overcome them. He was not always wrong by any means, but he was usually annoying. Professor Frederick Alexander Lindemann, 1st Viscount Cherwell (April 5, 1886 - July 3, 1957) was a physicist who became an influential scientific adviser to the British government and a close associate of Winston Churchill. ... Reflex klystron Type 2K25 or 723 A/B. The threaded adjustment rod on the right side allows the position of the reflector to be adjusted (by compressing the reflex cavity), and thus the natural resonant frequency of the device. ... A cavity magnetron is a high-powered vacuum tube that generates coherent microwaves. ...

Lord Cherwell did not want the secret of the magnetron to fall into German hands. Once the Germans understood it, they would not only try to duplicate it, but 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 core could survive even large self-destruct charges.

The H2S design team did not believe the klystron could do the job, and in fact 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 fortunately be proven wrong, though given the widespread parallel development of the cavity magnetron, in hindsight it wasn't an unreasonable assumption.

Despite all the problems, on 3 July 1942 Churchill held a meeting with brass and the H2S group, where he shocked 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 extreme 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. July 3 is the 184th day of the year (185th in leap years) in the Gregorian calendar, with 181 days remaining. ... This article is about the year. ... October 15 is the 288th day of the year (289th in Leap years). ...

Despite the extraordinary efforts of the TRE, there was no way to meet the 15 October deadline. By 1 January 1943, however, twelve Short Stirling and twelve Halifax bombers had been fitted with H2S. On the night of 30 January 1943, thirteen "Pathfinder" bombers, 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 for a strike. Seven of the Pathfinders had to turn back, but six marked the target successfully, which was hit by a hundred Lancasters. January 1 is the first day of the calendar year in both the Julian and Gregorian calendars. ... 1943 (MCMXLIII) is a common year starting on Friday. ... January 30 is the 30th day of the year in the Gregorian calendar. ... The Pathfinder squadrons of the Royal Air Force were elite squadrons of RAF Bomber Command during World War II. During World War II the RAF Bomber Command practiced mainly night bombing. ... Hamburgs central promenade Jungfernstieg on the Alster lake, between 1900 and 1914 Hamburg is Germanys second largest city (after Berlin) and, with the Hamburg Harbour, its principal port. ...

The Germans did not know about H2S at the time. Unfortunately, on 2 February 1943, a Pathfinder Stirling was shot down near Rotterdam, and the Germans noticed the unusual gear in its wreckage. The British had been clever with electronics, and the Germans were careful to look for anything out of the ordinary in RAF aircraft forced down in the Reich. Most of the H2S set was recovered except for the display, and German engineers began to work on the "Rotterdam Gerät" (Rotterdam Device), as they called it, however the engineeers were puzzled as to what the equipment actually did. The equipment remained a puzzle, until about a year later a working display was recovered from another aircraft and the complete equipment set-up on one of Berlin's immense concrete flak-towers. When the equipment was switched on and the onlookers saw the display they were horrified, the display recognizably showing Berlin's other flak towers and surrounding area. When Hermann Göring was shown this, he is said to have exclaimed "My God! the British really can see in the dark". February 2 is the 33rd day of the year in the Gregorian Calendar. ... The Stirling was a World War II heavy bomber design built by Short Brothers. ... For other places named Rotterdam, see Rotterdam (disambiguation) Rotterdam ( â–¶ (help· info)), located in the province of Zuid Holland, is the second largest municipality in the Netherlands (after Amsterdam), yet depending on the calculation methods the agglomeration in which Rotterdam is situated vies with the Amsterdam agglomeration for first spot in... The word flak can mean:- Anti-aircraft gunfire, derived from the German Flugabwehrkanone, for aircraft defense cannon, during World War II. See also 88 mm gun criticism, as a metaphorical extension of the previous, e. ... Hermann Göring Hermann Wilhelm Göring (also Goering in English) (January 12, 1893 – October 15, 1946) was an early member of the Nazi party, founder of the Gestapo, and one of the main leaders of Nazi Germany. ...

Bomber Command didn't use H2S in a big way until that summer. On the night of 24 July 1943, the RAF began Operation Gomorrah, a large-scale systematic attack on Hamburg. At that time, H2S was fitted also to Avro Lancaster, 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 performing two daylight attacks in between the three RAF raids. Large parts of the city were burned to the ground by a terrifying cyclone of fire. About 45,000 people, mostly civilians, were killed. Firestorm in Hamburg Operation Gomorrah was the military codename for a series of air raids conducted by the Royal Air Force on the city of Hamburg beginning in the end of July 1943. ... The Avro Lancaster was a four-engine World War II bomber aircraft made initially by Avro for the Royal Air Force (RAF). ... USAAF recruitment poster. ...

H2S was noteworthy for introducing the Plan Position Indicator, or PPI the rotating-map display that is now familiar to radar operators the world over. The Plan Position Indicator, known as PPI is the most common way to represent radar data. ... In chemistry, pyrophosphate, or PPi is an anion observed in living systems, usually formed by the hydrolysis of ATP into AMP. The hydrolysis is called pyrophosphorolysis. ...

Adapted from Microwave Radar At War (1). There is a open source verification for this text on the home page Greg Goebel / In The Public Domain.

See also

• List of World War II electronic warfare equipment

List of World War II electronic warfare equipment and code words Airborne Cigar (A.B.C.) - Jamming transmitter carried by 101 Sqn Lancasters using 8th crew member to monitor and then jam German nightfighter frequencies Berlin - German night fighter radar, introduced April 1945, centrimetic radar (9cm) Boozer - Fighter radar early...

References

• A. P. Rowe: One Story of Radar - Camb Univ Press - 1948
• Dudley Saward, Bernard Lovell: A Biography - Robert Hale - 1984

External links

• Bournemouth University Radar Recollections site