The Yak-3U was a modified version of the Yak-3 that was powered by a Shvetsov ASh-82FN radial engine. To reduce weight, its plywood fuselage skin and formers, fabric-covered ailerons, wooden stabilizer and fin, and steel elevator control rods were replaced with duralumin components. Initially, the wing remained wooden, but its span was increased to 9.4 meters, increasing the wing area to 15.35 square meters. The wing was moved forward by 219 mm to maintain proper balance, and the cockpit was raised by 84 mm to improve the pilot's visibility.

Construction of the prototype began in Novosibirsk on January 20, 1945, and was completed in Moscow on April 23. Factory trials took place at Moscow’s Central Airfield from April 29 to June 9, 1945. Afterward, the aircraft was returned to the design bureau for further refinement. One of the changes was replacing the wooden wing with an all-metal one, which reduced the aircraft’s weight to 2,740 kg. However, by that time, the war had ended, and the need for a new fighter had largely disappeared. The aircraft was eventually canceled and never entered mass production.

The Yak-3U was introduced in Update 1.89 "Imperial Navy". It combines excellent maneuverability with impressive acceleration and overall flight performance. Above 4km, however, it loses this performance advantage rapidly and its maximum speed limit is very limited.