On February 21, 1949 a Sovmin order requested the Yakovlev OKB to design a lightweight, radar-equipped, all-weather and night interceptor capable of Mach 0.97 at 4,000 m (13,000 ft). The aircraft was to utilize the Klimov VK-1 engine which first appeared on Mikoyan-Gurevich MiG-15 and MiG-17 fighters. This engine was itself a Soviet copy of the British Rolls-Royce Nene centrifugal turbojet initially known as the RD-45. The leading fighter OKBs each created a prototype to meet the requirement, which included the Lavochkin La-200, Mig I-320, Suchoi Su-15 (unrelated to the later aircraft with the same designation) and the Yak-50 (again, unrelated to the later aircraft). A major difference was that while Yakolev used one engine, the other design bureaus used two.