page_title: ASV Mark II radar
section_title: ASV Mk. II
hierarchical_section_title: ASV Mark II radar / Development / ASV Mk. II
caption_attribution_description: English: A Fairey Swordfish in Flight Close-up of a Fairey Swordfish Mark II, HS 545 'B', in flight as seen through the struts of another aircraft, probably while serving with No 824 Squadron, Fleet Air Arm, 1943-1944.
context_page_description: Radar, Air-to-Surface Vessel, Mark II, or ASV Mk. II for short, was an airborne sea-surface search radar developed by the UK's Air Ministry immediately prior to the start of World War II. It was the first aircraft mounted radar of any sort to be used operationally. It was widely used by aircraft of the RAF Coastal Command, Fleet Air Arm and similar groups in the United States and Canada. A version was also developed for small ships, the Royal Navy's Type 286.
  The system was developed between late 1937 and early 1939, following the accidental detection of ships in the English Channel by an experimental air-to-air radar. The original ASV Mk. I entered service in early 1940 and was quickly replaced by the greatly improved Mk. II. A single Mk. II was shipped to the US during the Tizard Mission in December 1940, where it demonstrated its ability to detect large ships at a range of 60 miles. Production was immediately taken up by Philco in the US and Research Enterprises Limited in Canada, with over 17,000 produced for use in the US alone.
  It was Mk.
context_section_description: Based on the experiences of the Mk. I units in the field, in January 1940 Gerald Touch began designing a new set while working at the RAE. Hanbury Brown joined him in February 1940.
  The new ASV Mk. II design was essentially a rationalized and cleaned up Mk. I, differing little in terms of the electronics, but considerably in terms of layout, wiring and construction. Among the changes was the separation of the receiver electronics from the display so either could be fixed by swapping them out separately, and using a selection of standard electrical connectors on all of the cables.
  As a result, Mk. II was far more reliable than Mk. I; it did not offer increased performance, but maintained that performance in spite of rough service and was much easier to fix in the field. The only other major change was to move the operational frequency from 214 MHz to 176 MHz because it was found the Mk. Is were interfering with naval radio beacons.
  An order for 4.000 units was placed with EKCO and Pye. For reasons unknown, the contract negotiations required considerable time to finalize, and throughout the production run it battled for precedence with the AI units and Chain Home Low which also made use of the Pye strip. The first Mk. II units began to arrive in the summer of 1940, and by October 1940, 140 transmitters, 45 receivers and 80 displays had been delivered. By the end of March 1941 that had increased to 2,000 transmitters and 1,000 receivers.
  Mk. II scored its first success on 30 November 1940 when a Whitley Mk. VI damaged U-71 in the Bay of Biscay. On 26 May 1941, a Fairey Swordfish equipped with Mk. II detected the Bismarck as it attempted to return to France for repairs. This detection led to the Bismark's sinking the next day. By mid-1941 the ASV radar had increased daytime attacks on U-boats by 20%, and made night attacks possible for the first time. The first successful night attack on a U-boat was carried out by a Swordfish on 21 December 1941.
caption: Compact Yagis were mounted to the wing struts on the Fairey Swordfish. A system like this one was responsible for detecting, and ultimately sinking, the Bismarck.
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