in all weather conditions at altitudes up to its service ceiling. As well as the radar, the aircraft was equipped with an SRO-1 IFF transponder, an RSIU-3 Klyon VHF radio, and an AP-28 autopilot. To set up an automatic landing approach in bad weather, the Yak included a Materik (Russian for continent) Instrument landing system. The Pozitron-1 system completed the aircraft's avionics systems, and was likely a command link system. The aircraft's wings, tail unit, and air intakes were equipped with hot air de-icing, while the foreign object damage protection screens and intake center-bodies of the engines were de-iced electrically, enabling the Yak to remain at colder high altitudes for longer times and to operate in regions with a cold climate. Despite its complex and heavy avionics, the aircraft had a lightweight airframe for a twin-engined fighter, due to a design that reduced structural weight to the minimum. Two prototypes and a static test mockup were built by Yakovlev. The first prototype flew on 19 June 1952, piloted by Yakovlev test pilot Valentin Volkov. Manufacturer testing continued until November. The Yak-120 exceeded the Air Force specific operational requirements in all aspects except for speed and range. Its 3-hour and 45 minute endurance without a drop tank (4 hours and 15 minutes with tank) and 2,800 km range on internal fuel at 12,000 m altitude allowed it to fly long-range patrols. Being smaller and lighter, it surpassed the performance of the competing Lavochkin La-200B. However, the aircraft could not be submitted for state acceptance trials due to delays in the development of the RP-6 radar. As a result, the RP-1 Izumrood radar was fitted as a temporary substitute in early December. The Yak-120 was tested at the Scientific Research Institute of the Air Force (NII VVS) with the RP-1 between May and June 1953. With mostly positive results, the aircraft was authorized for production with the service designation Yak-25. The test results from the NII VVS were approved as specifications for the Yak-25 by a Council of Ministers directive on 8 September. Production and Yak-25M The Yak-25s were built at Factory No. 292 in Saratov, with the first aircraft completed in September 1954. Due to slight modifications, the radar of these aircraft was known as the RP-1D. However, very few aircraft were built to the original standards, due to the fact that the RP-6 had been fully developed by the end