page_title: H2X
section_title: Pathfinder missions
hierarchical_section_title: H2X / Pathfinder missions
caption_attribution_description: English: The image shows a B-17 Flying Fortress bomber as seen from another B-17's H2S display. The H2X was a ground-scanning radar used by the USAAF in the late WWII period. It was a development of the British H2S using a new magnetron that worked in the S-band rather than the X-band. This gave the H2S higher resolution, enough to make a clear image of an aircraft in this case.
context_page_description: H2X, officially known as the AN/APS-15, 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. It was also known as the "Mickey set" and "BTO" for "bombing through the overcast" radar.
  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 initially considered using H2X as well, but would instead develop their own X band system, the H2S Mk. III. The RAF system entered service in late 1943, before the first use of H2X in early 1944.
  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 powered strategic bombers that entered service.
context_section_description: The first H2X-equipped 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 RAF practice of using highly trained Pathfinder crews to go in before the main bomber stream and identify and mark the target with flares. 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 H2X on later 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. The first use of Mickey was against Ploiești on April 5, 1944.
caption: 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.
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