Complex sentence: Prior to World War II Yakovlev was best known for building light sports aircraft, his Yak-4 light bomber impressed the Soviet government enough to order the OKB to design a new fighter with a Klimov M-106 V-12 liquid-cooled engine.
Split into simpler sentences: Prior to World War II, Yakovlev was best known for building light sports aircraft. His Yak-4 light bomber impressed the Soviet government enough to order the OKB to design a new fighter with a Klimov M-106 V-12 liquid-cooled engine.