In 1943, Yakovlev designed Yak-1M which was a smaller and lighter version of Yak-1. A second Yak-1M prototype was constructed later that year, differing from the first aircraft in plywood instead of fabric covering of the rear fuselage, mastless radio antenna, reflector gunsight, and improved armor and engine cooling. The chief test pilot for the project Piotr Mikhailovich Stefanovskiy was so impressed with the new aircraft that he recommended that it should completely replace Yak-1 and Yak-7 with only Yak-9 retained in production for further work with the Klimov VK-107 engine. The new fighter, designated Yak-3 entered service in 1944, later than Yak-9 in spite of the lower designation number. A total of 4,848 aircraft were produced.