Preparations for Yak-3 production started immediately, but the production tempo could not be allowed to falter during conversion to the new aircraft. So Plant No.292 mastered the manufacture of the fighter in the winter of 1944 while maintaining its average monthly output of 250 Yak-1 s. First production Yak-3 was rolled out on 1st March 1944.
Production aircraft differed from the second prototype in numerous but minor ways. Initial production Yak-3s had exactly the same armament as the Yak-I, as production of the ShA-20M cannon had not yet begun. Because of low manufacturing standards, production Yak-3s had poorer flight performance than the second prototype. The loss of speed was about 9.3 to 12.4mph (15 to 20 km/h), and time to attain an altitude of 16,400ft (5,000m) increased by 0.5 minute. Increased loads on the control surfaces had an adverse effect on horizontal manoeuvrability.
The new warplanes began to reach fighter aviation regiments during the summer of 1944, when the Soviet Command was preparing to launch large scale offensives. Yak-3 service tests were conducted by the 91st Fighter Regiment of the 2nd Air Army, commanded by Lt Colonel Kovalev, in June-July 1944. The regiment was tasked with gaining supremacy in sky. In the course of the L'vov operation almost half of its pilots flew their first combat mission, and all of the regiment's pilots had begun a higher standard of training. During the service tests 431 missions were flown, including interception, on-call missions, missions for building up forces, and freelance operations. Twenty Luftwaffe fighters and three Junkers Ju87 bombers were shot down in air combats, while Soviet losses numbered two Yak-3s shot down, plus three that were damaged by German anti-aircraft defences but managed to reach Soviet-held territory.
Operations showed that the innovative Soviet fighter could catch its German counterparts in horizontal flight as well as in climbing and diving manoeuvres. The Yak-3 gained a substantial advantage over the Fw190A within two nose-to-tail turns, and over the Bf109G within three turns.
A large dogfight occurred on 16th June 1944. Both sides built up their forces, with the result that 18 Yak-3s opposed 24 German fighters, and 15 Luftwaffe aircraft were shot down for the cost of one Soviet fighter destroyed and one damaged. Next day, Luftwaffe activity over that section of the front had virtually ceased. Service tests indicated that the Yak-3 appeared to be most suitable for air defence missions. Its use for close support of ground troops, bomber escort and so on was less worthwhile owing to its limited supply of fuel, average mission duration being limited to about 40 minutes.
The tests also revealed certain short-comings of the initial production Yak-3. Instances were pointed out when a main undercarriage leg folded during take-off or landing and taxying, owing to failure of the undercarriage ram and oleo strut attachment. However, in general the Yak-3 was easy to operate, and maintenance crews and pilots found it easy to adapt to the new aircraft.
Assessing the fighter, Lieutenant General Walter Schwabedissen wrote in the book The Russian Air Force in the Eyes of German Commanders: 'Whereas the German Bf109G and Fw190 models were equal to any of the aforementioned Soviet fighter models in all respects, this cannot be said of the Soviet Yak-3, which made its first appearance at the front in the late Summer of 1944. This aeroplane was faster, more manoeuvrable and had better climbing capabilities than the Bf109G and Fw190, to which it was inferior only in armament'.
Luftwaffe fighters in combat with the Yak-3 tried to exploit surprise. This happened on 17th September 1944, when Fw 190s attacked a formation of three Yak-3s of the 66th Fighter Air Regiment over the Riga district of the front by coming out of the sun, shooting down two of the Soviet aircraft. On 23rd September the regiment gained its revenge when a Yak-3 formation led by Major I Vitkovsky shot down seven Fw 190s in a single dogfight.