The NS-45 was created as a result of a July 1943 decision of the State Defense Committee to arm Soviet fighters with 45 mm autocannons.

The former proposed an enlarged version of their unreliable Shpitalny Sh-37; although they made a prototype that passed factory tests in a LaGG-3, their 45 mm gun was not accepted for state trials because of the known issues with the Sh-37 design.

[8] The theoretical weight of fire of the Yak-9K was 5.53 kg/s (12.2 lb/s), which gave it a considerable advantage in this department relative to most single-engine German aircraft of the time except the "flying gun-batteries" such as the Fw 190A-6/R1 or the Bf 109G-6/R6.

[7] Developed in late 1943, the Yak-9K prototype was tested at the Central Research Institute of the Soviet Air Force (VVS NII) between January 12 and April 8, 1944.

[8] Between April and June 1944 a limited production run of the aircraft, with the cockpit pushed further to the back to improve the center of gravity, was manufactured at a plant in Novosibirsk and delivered for military trials to the 3rd Fighter Air Corps.

[8] Combat experience with the Yak-9K showed that although the NS-45 cannon proved deadly to enemy aircraft, realistically only its first shot could be aimed.

[5] To compensate for the Yak-9K's poor maneuverability in the vertical plane, pilots of the 812th IAP developed tactics that essentially employed the aircraft as a heavy fighter, using it for surprise attacks on bombers, and providing it with an escort by nimbler Yak-3s flying top cover.

[3] Besides the reliability and airframe performance issues, another contributory reason was that the German bombers still active on the Eastern front at this point in the war were mainly Fw 190 Jabo, and the 45 mm shell was overkill for these.

[3] On August 20, 1943, the People's Commissariat of Aviation Industry of the USSR ordered that an Il-2 be tested with the new 45 mm aircraft guns.

[10] The results were disappointing; the Il-2-mounted NS-45s exhibited poor accuracy hitting tank-size targets and their recoil was almost twice what the Il-2's wings could safely handle (about 4000 tons-force).

[3] A more substantial test program took place between 30 December 1946 and 3 October 1947 with the Tupolev Tu-1 night fighter prototype, which was fitted with two NS-45s in the nose—each one supplied with 50 rounds—and with two NS-23s in the wing roots.