page_title: ASV Mark III radar
section_title: IIIC
hierarchical_section_title: ASV Mark III radar / Improved versions / IIIC
caption_attribution_description: English: Aircraft of the Royal Air Force 1939-1945- Short S.25 Sunderland. Sunderland GR Mark V, ML778 "NS-Z", piloted by Wing Commander J Barrett, the Commanding Officer of No. 201 Squadron RAF based at Castle Archdale, County Fermanagh, flying the last operational sortie of the war undertaken by Coastal Command.
context_page_description: Radar, Air-to-Surface Vessel, Mark III, or ASV Mk. III for short, was a surface search radar system used by RAF Coastal Command during World War II. It was a slightly modified version of the H2S radar used by RAF Bomber Command, with minor changes to the antenna to make it more useful for the anti-submarine role. It was Coastal Command's primary radar from the spring of 1943 until the end of the war. Several improved versions were introduced, notably the ASV Mark VI, which replaced most Mk. IIIs from 1944 and ASV Mark VII radar, which saw only limited use until the post-war era.
  Coastal Command's first radar was ASV Mark I, which began experimental use in 1939. Minor improvements were made for the Mark II in 1940 but it was not widely available until late 1941. Having realized that the RAF was using radar to detect their U-boats, in the summer of 1942 the Germans introduced the Metox radar detector to listen for their signals. This gave the submarine a warning of the aircraft approach long before the submarine became visible on the aircraft's radar display.
context_section_description: By 1943 the Short Sunderland flying boat was a major part of the Coastal Command fleet. These had been using ASV Mark II, whose antennas were mounted under the wings or on either side of the fuselage. Mark III presented a problem as the nose and belly locations that gave the required all-round view could not be used due to the boat hull of the aircraft. This led to a modified version known as Mark IIIC. IIIC used two scanners, one under the outer section of each wing. Their rotation was synchronized to one drive and the radio signal switched between them during the rotation. To maintain coverage in the important dead-ahead area, the signal did not switch to the port-side (left) scanner until 15° past dead-ahead, so the starboard-side (right) scanner covered 195°, not 180. The signal was provided by a magnetron, piped to the scanners via a waveguide run through the leading edge of the Sunderland's massive wing. In tests carried out in April 1944, the IIIC demonstrated greatly improved performance over the Mk. IIIs in Wellington and Halifax, as much as double, although the reasons were never fully determined.
caption: The well-faired radomes of the Mark IIIC produced less drag than the large antenna sets of the Mark II.
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