AI Mk. X

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The AI Mk. X or Airborne Interception radar, Mark X is a British airborne target detection (search) radar. The AI Mk. X is the British version of the American Signal Corps Radio model 720 or SCR-720 radar, and in-game specific British and American aircraft utilise it.

Vehicles equipped with this radar

General info / usage

A front view of an P-61 with an AI Mk. X radar.

Being only a target detection radar the AI Mk. X cannot track targets or provide a firing lead indicator. However, it has an acceptable detection range of up to 14,000 m and a rapid scanning speed completing a sweep in approximately 0.17 seconds (5.8 sweeps per second).

General Characteristics
Range Settings
14,000 m 8,500 m 150 m 3 km, 9 km, 18km
Search Modes
Search Mode Azimuth Scan
Elevation Scan
Scan Time
Default ±75° -20°/+40° 0.17s

Comparison with analogues

A view of a BC-1152-A pilots indicator portion of the AI Mk. X radar in the cockpit of a P-61. (The BC-1152-A is the square box with the rectangular window just above the control yoke)

Compared to wartime radars like the German FuG 202 and FuG 220 the AI Mk. X has a much wider scanning arc and better range; however does not update instantly, unlike German radars. Compared to the post-war Allied AN/APS-21 search radar, the AI Mk. X has an inferior range and narrower scanning angles but scans much faster.

Comparable airborne radar units to AI Mk. X
Name Min Range Accurate Range Max Range Azimuth Angle Elevation Angle Scan Time
FuG 202 200 m 4,000 m 4,000 m ±30° ±30° Instant
FuG 220 500 m 5,000 m 5,000 m ±35° -55°/+20° Instant
AN/APS-21^ 1,000 m 28,000 m 45,000 m ±85° ±16° 3.00 s

Pros and cons


  • Respectable 14,000 m max range
  • Rapid scanning
  • Decent scanning angles


  • Inferior range and scanning angles compared to some higher rank radars


A view of the BC-1151-A indicator observers unit of an AI Mk. X in the cockpit of a De Haviland Mosquito.

The AI Mk. X (Airborne Interception radar, Mark X) is a British version of the American SCR-720 Radar. The SCR-720 was a development of the SCR-520 radar, which was in turn developed using the knowledge gained from the development of the British AI Mk. VIII radar (the first operational microwave-frequency air-to-air radar). The story of the Airborne Interception (AI) family of radars began in Britain, in late 1935 with the successful testing of the Chain Home system (an early ground-based early warning radar), in which it was proven capable of detecting aircraft at ranges of over 64 km (the range would eventually improve to 160 km). Plans were soon put in place to begin building Chain Home stations along the south coast of England, in preparation for any potential air attack on Britain.

The chain home system could detect an aircraft at a maximum accuracy of one mile, but it took time to communicate this information to air-crews. The resulting delay between detection and communication to the crews reduced location accuracy to five miles, due to the aircraft moving from the initial reported position. Tracking aircraft would not be a problem for daylight interceptions as fighter pilots could easily spot a plane five miles away, but the reduced accuracy would make the radar system much less effective at night. Henry Tizard, who was leading the implementation of Chain Home, began to fear that the radar system might become too effective. He predicted that if the Luftwaffe ever attacked Britain, it would lead to the Germans suffering enough losses which would force them to switch to nighttime operations, in which case Chain Home would lose its effectiveness. He raised his concerns, and in August 1936 a project was started to develop a radar system which could be fitted onto an aircraft; the plan was that at night Chain Home could guide interceptors to the general area of enemy aircraft, at which point the pilots would switch to using their radars to find the exact location of the enemy aircraft.

A view of the BC-1152-A pilot's unit of an AI Mk. X in the cockpit of a P-61 fighter.

In autumn 1936 the first-ever airborne radar system, known as RDF 1.5 was tested, it consisted of powerful ground-based transmitters and a receiver mounted on a Handley Page Heyford biplane bomber. Although capable of detecting aircraft 80 km away the system was deemed unworkable due to the need for a large number of ground-based transmitters, and having only a very narrow search angle (the transmitter, receiver aircraft and target aircraft needed to be roughly in line with each other). In March 1937, the Heyford was fitted with its transmitter and was able to detect targets a few miles away, and in September 1937 an Avro Anson outfitted with the same radar proved it could be used to identify shipping nearly 10 miles away in poor weather conditions. The rest of 1937 and 1938 refined the radar for ship detection and turning it into a workable system (instead of a battery-powered prototype). In 1939, with the prospect of war becoming inevitable, the focus switched back to detecting aircraft.

Through 1939, Mk.I, Mk.II and Mk.III versions of the Airborne Interception radar were produced and tested in limited service with the RAF. All of them suffered from various problems, most notably a high minimum range, low maximum range, or inadequate scan angles. In May 1940 the Mk IV was tested, it solved all the previous problems with a maximum range of 6 km, and a minimum range of only 150 m, a production order of 3,000 units were placed immediately, making the AI Mk. IV world's first airborne radar to enter service. Improved Mk. V, and Mk. VI versions of the detector saw limited RAF service.

The next significant AI radar to enter service was the AI Mk. VIII. The Mk. VIII was almost a complete redesign compared to the MK. IV. Instead of using static antennas like the Mk. IV, instead, the Mk. VIII used a spinning parabolic dish which focused its beam, improving range and reducing clutter. Critically the Mk. VIII was also the worlds first operational airborne radar to operate at microwave frequencies, offering much better performance than the Mk. IV which operated on VHF radio frequencies. The AI Mk. VIII entered service in 1941.

During the development of microwave frequency radars, and the AI Mk. VIII, a prototype was sent to America as part of the Tizard Mission. The Tizzard mission took place in 1940; a delegation of British scientists/engineers travelled to America to share Research and Development achievements. This plan was for American to be given access to British developments (including radar), in exchange for assistance with the war effort (provision of supplies etc.); and to allow America's vast industrial resources to exploit the R&D work completed by the UK, which Britain itself could not fully utilize due to the immediate requirements of war-related production. One of the British Scientists Edward "Taffy" Bowen remained in the US after the original visit and helped set up the MIT Radiation Laboratory which began developing airborne radars for the United States. Using the information gained from the British prototype, they made "remarkable" progress and soon produced the SCR-520 radar. The P-70 (a fighter aircraft version of the A-20 Havoc) and P-61 were the first two American aircraft outfitted with the primary SCR-520 radars.

After the implementation of the AI Mk. VIII development of a new radar the AI Mk. IX began. The Mk. IX would offer better performance than the MK. VIII and would have new features including target tracking. However, during a test flight on On 23 December 1942, the Beaufighter carrying the only radar prototype and Arthur Downing (the radar's lead developer) was attacked in a friendly fire incident, after being mistaken by two Spitfires for a German aircraft. The Beaufighter crashed into the sea, killing Downing and destroying the prototype. The loss of Downing and the radar prototype caused a significant delay in the British radar program. Around the same time in December 1942 the American Western Electric company (which had received the contract for production of American airborne radars) provided Britain with an example of the new SCR-720 radar. It was an improved and significantly lighted SCR-520, which would fit inside British aircraft (unlike the SCR-520). With their radar program delayed, British engineers passed some minor suggestions and upgrades to Western Electric, resulting in the SCR-720B. Britain placed an order for 2,900 SCR-720Bs under the name AI Mk. X. The AI Mk X entered service with the RAF in August 1943, fitted on night fighter versions of the Mosquito (and later on other aircraft).

The AI Mk.X remained in service until 1957, being fitted to night fighter version of the Gloster Meteor and the Sea Venom FAW 20.


An excellent addition to the article would be a video guide, as well as screenshots from the game and photos.

See also

External links