The Yakovlev Yak-9U was the sixth variant of the Yak-9 fighter aircraft family. The aircraft was based on the Yak-9T and included significant aerodynamic and structural upgrades similar to the Yak-3. The Yak-9U was powered by the new Klimov VK-107A engine, which produced 1,650 horsepower. The burst mass was 2.72 kg/s. During early test flights in 1943, the only comparable Soviet fighter was the Polikarpov I-185 prototype, but it was more difficult to fly and less agile due to its heavier weight. Except for the P-51B Mustang, which could achieve 710 km/h, the Yak-9U's peak speed of 700 km/h at 5,600 m was quicker than any other production fighter aircraft in the world at the time. Overheating issues during the test flight stage were resolved by expanding the radiators during production. It was the best high-altitude Soviet fighter of its time. The Yak-9U flew 398 sorties for a total of 299 hours. A total of 26 battles were fought, with the majority of them ending in victory.

Introduced in Update 1.37, the Yak-9U is one of the few Yak fighter planes that excels at operating at high altitudes. Unlike previous Yak-9s that were powered by the Klimov VK-105PF engine, the Yak-9U is powered by the Klimov VK-107A engine. As a result, the Yak-9U is among the quickest planes at sea level in its class. Overall, the Yak-9U combines impressive speed, acceleration, climb, and manoeuvrability but comes with a rather mediocre weaponry for its BR. The Yak-9U's engine improvement lets it maintain good performance up to 5,000 m, allowing players to engage in combat with other high-altitude enemy aircraft without being significantly disadvantaged.