page_title: ASV Mark II radar
section_title: ASV Mk. I
hierarchical_section_title: ASV Mark II radar / Development / ASV Mk. I
caption_attribution_description: English: This image shows the front-firing antennas of an ASV Mk. II radar as installed on a Royal Canadian Air Force Douglas Digby (B-18 Bolo) aircraft. Note the shaping of the transmitter antenna, seen just below the bombsight window. It has been bent into a curved shape to closely follow the shape of the aircraft fuselage, using the fuselage itself as a reflector to make a Yagi antenna using only a single wire. Similar "tricks" were used on a variety of ASV and AI radars, but made it difficult to move to different aircraft designs. This aircraft is part of 751 Squadron RCAF stationed at Rockcliffe (Ottawa). It is not clear whether this is the same aircraft as seen in other images.
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: In early August, the team was informed that the Air Ministry had ordered 30 AI units and expected Bowen to have them installed in Bristol Blenheim aircraft within 30 days. When the units started arriving, they found the Metrovick transmitter was also the bench model, and when they protested, Metrovick noted that Watt had personally visited the factory and told them to put it into production because it was known to work.
  To further confuse matters, when the war began on 1 September, the majority of the AMES team was hurriedly sent to a prearranged location at the University of Dundee in Scotland, only to find that nothing had been prepared. The rector had only vague memories of a conversation on the topic with Watt, and by now the students had returned for the fall term and there was little available room.
  Bowen's AI team was sent to a small airfield outside of Perth (some distance from Dundee) that was utterly unsuitable for fitting. Nevertheless, radar sets and aircraft started to arrive, along with new demands from the Fleet Air Arm to equip some of their aircraft with ASV in Swordfish and Walrus aircraft.
  At a meeting in London on 30 November 1939, the relative priorities for Chain Home, Chain Home Low, AI and ASV were discussed. Bowen finalized plans to build the ASV radios at EKCO using the new VT90 tubes (later known as CV62) in the transmitter, while the AI Mk. II would use the older DET12 and TY120s. This meant the ASV would be somewhat more advanced than AI.
  Another chance encounter after the meeting led Bowen to try a new material, polythene, from Imperial Chemical Industries (ICI) which produced excellent coaxial cable and neatly solved the electrical problems they had been having. It was soon in use throughout the industry.
  The first ASV using production parts was hand-fitted to a Walrus and sent to Gosport for testing. This version ran at a nominal 1.5 m wavelength, at 214 MHz. Flying at only 20 feet (6.1 m) over the water, the radar easily detected ships all around the Solent. Louis Mountbatten was watching this performance and immediately ordered one fitted to his destroyer, HMS Kelly. The Navy soon picked up development as the Type 286, and 200 such units would eventually be fitted to destroyers and torpedo boats.
  Meanwhile, Bernard Lovell had arrived at Perth, and through contacts in the Air Ministry, managed to convince them that the site was unsuitable for their work. A new location at RAF St. Athan in Wales was selected and the team moved into a hangar on the airfield in November 1939. Conditions turned out to be little better than Perth, and the team was forced to work in freezing temperatures as the hangar doors had to be left open. Nevertheless, by the end of December they had managed to fit 17 AI radars in Blenheims, and 3 ASVs in the newly arriving Coastal Command Lockheed Hudsons. January improved this to 18 AI and 12 ASV, numbers that continued to increase through the year.
caption: The Mk. I units used an antenna arrangement similar to the Mk. II unit seen on this RCAF Douglas Digby at CFB Rockcliffe. This particular aircraft also carried an experimental high-gain antenna under the wings, which cannot be seen here.
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