In the summer of 1951, the NKAP issued a requirement for an all-weather interceptor fighter possessing sufficient internal fuel capacity to mount standing patrols of up to 2.5 hours duration and capable of accommodating a large, new radar. This supplanted an earlier requirement to which the Mikoyan-Gurevich I-320 and Lavochkin La-200 had been evolved. The new radar, known as the Sokol (Falcon), had a 80cm diameter dish, three different scan modes and an installed mass weight of almost 500kg. To meet this new requirement, the Lavochkin and Yakolev OKBs respectively developed the La-200B and Yak-120. The latter, an all-metal stressed-skin tandem two-seater, was powered by a pair of small-diameter Mikulin AM-5A turbojets each rated at 2200kg / 4850-lb and hung beneath a wing swept back 45 degrees at quarter chord and carrying some 3 degrees of anhedral, and mounted in full-mid position. The undercarriage was of zero-track type, with wingtip-housed outrigger stabilisers, and armament comprised two 37mm N-37L cannon with their barrels accommodated in external fairings beneath the fuselage.
From 1957 the Mikulin AM 5 turbojets were replaced in the definitive Yak 25F by Tumansky RD 9s of 2600 kg (5730 lb) thrust, increasing the maximum speed.
The first of three Yak-120 prototypes was flown on 19 June 1952, State acceptance testing paralleling construction of a pre-series of 20 aircraft for avionics development and, commencing late 1953, service evaluation. With ballast equivalent in weight to the Sokol radar – which did not attain service status until late 1955 – the Yak-120 had a loaded weight of 9220kg, series production commencing late 1953 as the Yak-25 with RD-9 turbojets each rated at 2630kg. Confusing repetition of the “Yak-25” designation resulted from its initial use as an OKB appellation and subsequent use by the NKAP as an official and sequential designation, the previous Yakolev service fighter having been the Yak-23. The Yak-25 was assigned primarily to defence sectors in the Far North of the USSR, production being completed in 1958 after the delivery of 480 aircraft and service phase-out taking place in the mid ‘sixties.
The production programme took the type right through toward the end of the 1960s in role-differentiated models designated Yak-25, Yak-26 and Yak-27 with swept wings and on the Yak-25RD high-altitude reconnaisance version with straight wings.
The intercepter was codenamed Flashlight-A by NATO’s Air Standards Coordinating Committee, Flashlight B being a reconnaissance variant developed concurrently for service with the Soviet air force’s frontal aviation or tactical air arm.
A tactical reconnaissance derivative with the navigator accommodated in a glazed nose was built in 1953 as the Yak-125, but was not produced in series owing to prior adoption of the IL-28R. Other derivatives of the basic design were the Yak-25L ejection-seat test bed with individual cockpits, and the Yak-25RV long-range high-altitude strategic reconnaissance aircraft.
The Yak 25R carried the second crew member in a pointed glazed nose instead of behind the pilot, and armament was reduced from the intercepter’s pair of 37 mm (1.46 in) NR 37 cannon to a single 23 mm (0.90 in) weapon in the right-hand side of the forward fuselage.
Engines: 2 x Klimov VK-5, 8820 lb thrust
Max take-off weight: 10900 kg / 24031 lb
Wingspan: 11.00 m / 36 ft 1 in
Length: 15.67 m / 51 ft 5 in
Height: 4.32 m / 14 ft 2 in
Wing area: 28.94 sq.m / 311.51 sq ft
Max speed: 1090 km/h / 677 mph
Cruise speed: 820 km/h / 510 mph
Ceiling: 13900 m / 45600 ft
Range: 2730 km / 1696 miles
Armament: 2 x 37m cannon
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