page_title: AI Mk. VIII radar
section_title: GL sideline
hierarchical_section_title: AI Mk. VIII radar / Development / GL sideline
caption_attribution_description: English: Leeson House Langton Matravers near Swanage Dorset. A residential field studies centre.see more http://www.dorsetforyou.com/index.jsp?articleid=2607 See supplemental for info on Wartime use.
context_page_description: Airborne Interception radar, Mark VIII, or AI Mk. VIII for short, was the first operational microwave-frequency air-to-air radar. It was used by Royal Air Force night fighters from late 1941 until the end of World War II. The basic concept, using a moving parabolic antenna to search for targets and track them accurately, remained in use by most airborne radars well into the 1980s.
  Low-level development began in 1939 but was greatly sped after the introduction of the cavity magnetron in early 1940. This operated at 9.1 cm wavelength, much shorter than the 1.5 m wavelength of the earlier AI Mk. IV. Shorter wavelengths allowed it to use smaller and much more directional antennas. Mk. IV was blinded by the reflections off the ground from its wide broadcast pattern, which made it impossible to see targets flying at low altitudes. Mk. VIII could avoid this by keeping the antenna pointed upward, allowing it to see any aircraft at or above its own altitude.
  The design was just beginning to mature in late 1941 when the Luftwaffe began low-level attacks. A prototype version, the Mk. VII, entered service on the Bristol Beaufighter in November 1941.
context_section_description: At this point the AI team was moved from their location at St. Alban's to a new one at a former girls' school, Leeson House, outside Langton Matravers. A new lab had to be constructed on-site causing further delays, but by the late summer of 1940 the magnetron system was effectively operational at the new site.
  Meanwhile, the Army had been very impressed with the performance of the 25 cm experimental sets and became interested in using it as a range finder in a Gun Laying radar. Operators would point the radar at targets indicated to them by search radars, and from then on the radar information would be fed to the analogue computers that aimed the guns. Power was not a serious concern in this case as the range would be relatively short. The Air Defence Experimental Establishment (ADEE) of the Army was working on this using the klystron design from Birmingham and British Thomson-Houston (BTH) as their industrial partner.
  According to Dee, in September 1940 when Rowe heard of this he attempted to take over the project. After a 22 September meeting with Philip Joubert de la Ferte, Rowe built a GL team under the direction of D. M. Robinson using several members of the AIS team, telling them that they would have to focus on the GL problem for the next month or two. This led to increasing friction between Dee and Rowe, and especially Rowe's right-hand-man, Lewis. Dee claimed that Rowe was "seizing this opportunity to try and filch the GL problem from the ADEE" and that "only Hodgkin is carrying on undisturbed with AIS, and Lovell and Ward are fortunately engaged upon basic work with aerials and receivers and are therefore relatively undisturbed by this new flap."
  According to Lovell this did not represent as much of a disruption as Dee believed; to some extent, the klystron work at Birmingham had been instigated by the Army for GL purposes, so it was not entirely fair to complain. Lovell's primary task during this period was developing a conical scanning system that improved the accuracy of the radar beam many times, enough to allow it to be used directly to lay the guns (that is, about the same accuracy as optical instruments). This did not really require much effort, and would be useful for any centimetric radar, including AIS.
  Shortly thereafter, on 21 October, Edgar Ludlow-Hewitt, Inspector General for the RAF, visited the team. After the visit, Rowe told the team that a complete GL set had to be ready for fitting to a gun in two weeks. By 6 November Robinson had assembled a prototype system, but by 25 November he sent a memo to Rowe and Lewis stating that in the last 19 days, the system had only worked for two days due to a wide variety of problems. In December he was told to take the work completed so far to BTH for development into a deployable system. On 30 December 1940, Dee commented in his diary that:
  The GL fiasco has ended up with the whole thing being moved en bloc to BTH, including two AMRE staff. Nothing ever worked properly at Leeson and Robinson is feeling that it has been very salutary for Lewis to learn how haywire all the basic technique really is.
  Although the project was soon out of the AMRE's hands, development at BTH continued. The Ministry of Supply changed the specification to a magnetron in January 1941, requiring further development but producing a version of much greater range and utility. It was not until 31 May that the first set was delivered for testing, at which point information on the system was turned over to Canadian and US firms for building. The Canadian versions were eventually deployed as the GL Mk. III radar, while the US team at the Radiation Laboratory added an automatic scanning feature to their version to produce the superb SCR-584 radar.
caption: Leeson House was a significant improvement from the huts they formerly occupied, but the AI team was only here for eighteen months before moving once again.
exif: {"Image Make": "Canon", "Image Model": "Canon PowerShot A40", "Image Orientation": "Horizontal (normal)", "Image XResolution": "180", "Image YResolution": "180", "Image ResolutionUnit": "Pixels/Inch", "Image DateTime": "2006:03:01 11:15:58", "Image YCbCrPositioning": "Centered", "Image ExifOffset": "196", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "180", "Thumbnail YResolution": "180", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "2036", "Thumbnail JPEGInterchangeFormatLength": "5475", "EXIF ExposureTime": "1/125", "EXIF FNumber": "8", "EXIF ExifVersion": "0220", "EXIF DateTimeOriginal": "2006:03:01 11:15:58", "EXIF DateTimeDigitized": "2006:03:01 11:15:58", "EXIF ComponentsConfiguration": "YCbCr", "EXIF CompressedBitsPerPixel": "3", "EXIF ShutterSpeedValue": "223/32", "EXIF ApertureValue": "6", "EXIF ExposureBiasValue": "0", "EXIF MaxApertureValue": "97349/32768", "EXIF MeteringMode": "Pattern", "EXIF Flash": "Flash did not fire, auto mode", "EXIF FocalLength": "173/32", "EXIF FlashPixVersion": "0100", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "1600", "EXIF ExifImageLength": "1200", "Interoperability InteroperabilityIndex": "R98", "Interoperability InteroperabilityVersion": "[48, 49, 48, 48]", "Interoperability RelatedImageWidth": "1600", "Interoperability RelatedImageLength": "1200", "EXIF InteroperabilityOffset": "1412", "EXIF FocalPlaneXResolution": "800000/103", "EXIF FocalPlaneYResolution": "240000/31", "EXIF FocalPlaneResolutionUnit": "2", "EXIF SensingMethod": "One-chip color area", "EXIF FileSource": "Digital Camera", "EXIF CustomRendered": "Normal", "EXIF ExposureMode": "Auto Exposure", "EXIF WhiteBalance": "Auto", "EXIF DigitalZoomRatio": "1", "EXIF SceneCaptureType": "Standard"}