with five non-self-sealing fuel tanks in the fuselage that had a total capacity of of fuel. In addition it could carry a pair of drop tanks under the wingtips. The fighter was armed with two Nudelman-Rikhter NR-23 autocannon, each with 90 rounds. Two prototypes and a static-test airframe were ordered and the aircraft first flew on 8 July 1947 with the Hero of the Soviet Union, Lieutenant Colonel Mikhail Ivanov, at the controls. While still involved in its manufacturer's flight testing, the first prototype participated in the flypast at Tushino Airfield on 3 August. The Yakovlev OKB concluded its testing on 24 September and turned over the second prototype for state acceptance trials on 22 October. Although the Yak-23 was accepted for series production, it was criticized of heavy aileron and rudder forces, lack of cockpit pressurization and heating and ventilation, protection for the pilot and weak armament. The test pilots did praise it as highly maneuverable, with a good acceleration and takeoff and climb capabilities thanks to a high thrust-to-weight ratio. The second prototype was modified afterwards to address some of these issues and successfully tested again in 1948. Operational history The first aircraft were produced in a factory in Tbilisi in October 1949. In late 1949 they entered Soviet air force service. The Yak-23 was quickly replaced in the Soviet service with the more complicated swept-wing MiG-15, which offered superior performance. In all, only 316 Yak-23 aircraft were built before production ended in 1951. Apart from the fighter there were two trainer versions of the Yak-23 which were built in small numbers. The Yak-23UTI two-seat trainer which appears to have had the unusual arrangement of having the instructor seated in front of the student, and the Yak-23DC trainer which was produced in Romania. Small numbers of Yak-23s were exported to Czechoslovakia (20 from 1949, named S-101), Bulgaria (from 1949), Poland (about 100, from 1950), Romania (62, from 1951). Poland and Czechoslovakia acquired licenses for the aircraft, but built the superior MiG-15 instead. Yak-23s were withdrawn by the late 1950s, except in Romania which used them for another decade. U.S. testing A single Yak-23 was acquired by US intelligence via Yugoslavia in November 1953. The aircraft was a Romanian Yak-23 flown by Mihail Diaconu who had defected with it. The aircraft arrived disassembled and was shipped to the U.S. Air Force Test and Evaluation Center at Wright Field near