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{{Short description|American ground scanning radar system used during World War II}}
{{Infobox radar
[[File:1943 H2X Radar-French vers.png|thumb|400px|right|French-language diagram of H2X displays and equipment]]▼
| name = AN/APS-15
| image = [[File:H2X installation.jpg|290px|]]
| caption = Typical H2X installation, opposite the radio operator's position.
| country = USA
| introdate =
| number =
| type = [[air-to-ground]] radar system<ref name="Bailey2019">{{cite book|author=Steven K. Bailey|title=Bold Venture: The American Bombing of Japanese-Occupied Hong Kong, 1942-1945|url=https://books.google.com/books?id=btyDDwAAQBAJ&pg=PT207|date=March 2019|publisher=U of Nebraska Press|isbn=978-1-64012-162-1|pages=207–}}</ref>
| frequency =
| PRF =
| beamwidth =
| pulsewidth =
| RPM = <!--revolutions per minute-->
| range =
| altitude = <!--{{convert|X|m|ft|abbr=on}}-->
| diameter = <!--{{convert|X|m|ft|abbr=on}}-->
| azimuth = <!--X-Yº-->
| elevation = <!--X-Yº-->
| precision =
| power =
| other names =
}}
'''H2X''', officially known as the '''AN/APS-15''',<ref name="Brown1999">{{cite book|author=L Brown|title=Technical and Military Imperatives: A Radar History of World War 2|url=https://books.google.com/books?id=uYgsr3exvS4C&pg=PA548|date=1 January 1999|publisher=CRC Press|isbn=978-1-4200-5066-0|pages=548–}}</ref> was an American [[ground scanning radar]] system used for [[blind bombing]] during [[World War II]]. It was a development of the British [[H2S radar]], the first ground mapping radar to be used in combat.<ref name=Jablonski>{{cite book |last=Jablonski |first=Edward |year=1971 |title=Volume 2 (Wings of Fire), Book I (Kites over Berlin) |
H2X differed from the original H2S primarily in its [[X band]] 10 [[GHz]] operating frequency rather than H2S' [[S band]] 3 GHz emissions. This gave H2X higher resolution than H2S, allowing it to provide usable images over large cities which appeared as a single blob on the H2S display. The [[Royal Air Force
The desire for even higher resolution, enough to image individual docks and bridges, led to a number of variations on the H2X system, as well as the more advanced [[AN/APQ-7]] "Eagle" system. All of these were replaced in the post-war era with systems customized for the [[jet
==Usage==
▲[[File:1943 H2X Radar-French vers.png|thumb|400px|right|French-language diagram of H2X displays and equipment]]
H2X was used by the [[United States Army Air Forces|USAAF]] during [[World War II]] as a navigation system for daylight overcast and nighttime operations. It was introduced as an improvement of the earlier H2S set, which had been supplied to the US to aid in the war effort. While the [[RAF Bomber Command]] utilized ground mapping radar as an aid to night [[area bombing]], the primary use by the [[USAAF]] was as a fallback, to allow cities to be bombed even when hidden by cloud cover, an issue that had dogged their policy of precision daylight bombing since the start of the war, especially in cloud-prone Europe. With H2X, a city could be located and a general area targeted, night or day, cloud cover or no, with equal accuracy. H2X used a shorter 3 cm "centimetric" wavelength (10 [[GHz]] frequency) than the H2S, giving a higher [[angular resolution]] and thus a sharper picture, which allowed much finer details to be discerned, aiding in target identification.{{citation needed|date=December 2015}} H2S subsequently also adopted 3 cm in the Mark III version entering operational service on November 18, 1943, for “[[Battle of Berlin (air)|Battle of Berlin]]”).▼
▲H2X was used by the [[United States Army Air Forces|USAAF]] during [[World War II]] as a navigation system for daylight overcast and nighttime operations. It was introduced as an improvement of the earlier H2S set, which had been supplied to the US to aid in the war effort. While the [[RAF Bomber Command]] utilized ground mapping radar as an aid to night [[area bombing]], the primary use by the [[USAAF]] was as a fallback, to allow cities to be bombed even when hidden by cloud cover, an issue that had dogged their policy of precision daylight bombing since the start of the war, especially in cloud-prone Europe. With H2X, a city could be located and a general area targeted, night or day, cloud cover or no, with equal accuracy. H2X used a shorter 3 cm "centimetric" wavelength (10 [[GHz]] frequency) than the H2S, giving a higher [[angular resolution]] and thus a sharper picture, which allowed much finer details to be discerned, aiding in target identification.
H2X is not known to have ever been spotted by the German FuG 350 [[Naxos radar detector]], due to that receiving device's specific purpose being to spot the original British H2S equipment's lower frequency, 3 GHz emissions.
==Pathfinder missions==
[[File:H2X radar with B-17.jpg|thumb|The H2X's resolution was enough to produce good images of other aircraft, in this case, another B-17 Flying Fortress flying below the radar-carrying aircraft.]]
The first H2X-equipped [[Boeing B-17|B-17]]'s arrived in England in early October 1943, and were first used in combat on 3 November 1943 when the USAAF VIII Bomber Command attacked the port of Wilhelmshaven. Those missions where bombing was done by H2X were called "Pathfinder missions" and the crews were called "Pathfinder crews", after the RAF practice of using highly trained Pathfinder crews to go in before the main bomber stream and identify and mark the target with flares
{{more|Pathfinder (USAAF)|Pathfinder (RAF)}}
American practice used their Pathfinder crews as lead bombers, with radar equipped aircraft being followed by formations of radar-less bombers, which would all drop their loads when the lead bomber did. The ventral hemispherical [[radome]] for the H2X's rotating [[dish antenna]] replaced the [[ball turret]] on B-17 Flying Fortress Pathfinders, with the electronics cabinets for the "Mickey set" being installed in the radio room just aft of the bomb bay. The system was used extensively by The 91st Bomb Group in 1945 with occasional excellent but generally inconsistent results.<ref>{{Cite web|url=http://www.91stbombgroup.com/Dailies/322nd1945.html|title=322nd Dailies from 1945 - 91st Bomb Group (H)}}</ref>
The H2X on later [[Consolidated B-24|B-24 Liberators]] also replaced the ball turret, being made retractable as the ball turret was for landing on the Liberator. The operators panel was installed on the [[flight deck]] behind the co-pilot (where the radio operator's normal position was). In combat areas the Mickey operator directed the pilot on headings to be taken, and on the bomb run directed the airplane in coordination with the [[bombardier (air force)|bombardier]]. The first use of Mickey was against [[Ploiești]] on April 5, 1944.<ref name=Miller>{{cite book |last=Miller |first=Donald L. |year=2006 |title=Masters of the Air: America's Bomber Boys Who Fought the Air War Against Nazi Germany |url=https://books.google.com/books?id=5GMoWyUd41cC&pg=PA314 |location=New York |publisher=Simon & Schuster |isbn= 978-0-7432-3544-0 |page=118}}</ref>▼
▲The H2X on later [[Consolidated B-24|B-24 Liberators]] also replaced the ball turret, being made retractable as the ball turret was for landing on the Liberator. The operators panel was installed on the [[flight deck]] behind the co-pilot (where the radio operator's normal position was). In combat areas the Mickey operator directed the pilot on headings to be taken, and on the bomb run directed the airplane in coordination with the [[bombardier (air force)|bombardier]]. The first use of Mickey was against [[Ploiești]] on April 5, 1944.<ref name=Miller>{{cite book |last=Miller |first=Donald L. |year=2006 |title=Masters of the Air: America's Bomber Boys Who Fought the Air War Against Nazi Germany |url=https://
==Radar mapping of Germany==
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The sets tended to overload the Mosquito's electrical system and occasionally exploded. Mickey-equipped Mosquitos had the highest loss, abort, and mission failure rates of any version of the otherwise successful Mosquito reconnaissance aircraft, and were severely curtailed after February 19, 1945. Three were lost to enemy action and one was shot down by [[friendly fire]] from a Ninth Air Force [[Republic P-47 Thunderbolt|P-47]]. In Europe several [[Lockheed P-38 Lightning|P-38]] fighters were also converted to carrying H2X radar in the nose, along with an operator/navigator in a cramped compartment in the nose behind the radar dish, provided with small side windows and an access/exit hatch in the floor (much like the earlier P-38 "Droop Snoot" bomber-leader variants, but with a radome instead of a glazed nose). These missions were to obtain radar maps of German targets but plans to produce the variant in quantity never materialized.
==
In the [[Pacific War|Pacific theater]], [[Boeing B-29 Superfortress|B-29]]’s were equipped with the improved H2X radar called the [[AN/APQ-13]], a ground scanning radar developed by Bell, Western Electric, and MIT. The radome was carried on the aircraft belly between the bomb bays and was partially retractable. The radar operated at a frequency of 9,375 ± 45 megahertz and used a [[superheterodyne receiver]]. The radar was used for high altitude area bombing, search and navigation. Computation for bombing could be performed by an impact predictor. A range unit permitted a high degree of accuracy in locating beacons.
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==See also==
*[[AN/APQ-7]], an advanced
===Lists===
*[[List of radars]]
*[[List of military electronics of the United States]]
==References==
{{reflist}}
*Freeman, Roger A. ''The Mighty Eighth War Diary'' (1990). {{ISBN|0-87938-495-6}} page 240{{Specify|FOR WHAT INFO IN THE ARTICLE IS THIS A CITATION|date=March 2010}}▼
===Bibliography===
▲*Freeman, Roger A. ''The Mighty Eighth War Diary'' (1990). {{ISBN|0-87938-495-6}} page 240
*{{cite book |last1=Watson |first1=Raymond C. |title=Radar Origins Worldwide: History of its Evolution in 13 Nations through World War II |date=2009 |publisher=Trafford Publishing |location=n.p. |isbn=978-1-4269-2111-7}}
[[Category:Aircraft radars]]
[[Category:X band radar]]
[[Category:World War II radars]]
[[Category:World War II American electronics]]
[[Category:Military radars of the United States]]
[[Category:Military equipment introduced from 1940 to 1944]]
[[Category:Military electronics of the United States]]
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