Nudelman-Suranov NS-45

This Yak-9T modified to take the NS-45 gun became the first Yak-9K prototype

In fighters, the NS-45 gun was first installed on a modified Yak-9T, which was normally armed with a NS-37 gun. This aircraft, with constructor number 0121, effectively became the first Yak-9K prototype.[6] The "K" suffix stood for "Krupnokalibernyi", meaning large caliber.[3] The protruding barrel and muzzle brake of the NS-45 made the Yak-9K some 20 cm longer than the Yak-9T.[6] The NS-45 was supplied with 29 rounds of ammunition in the Yak-9K,[3][7] which were fed using a belt.[7] The only other armament installed on the Yak-9K was a UBS (a propeller-synchronized 12.7 mm machine gun) supplied with 200 rounds of ammunition.[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. Compared to these, the Yak-9K maintained however good horizontal maneuverability because its wings were not loaded with armament.[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.[7] For military (combat) trials 44 Yak-9Ks of this limited production run were used. These trials took place between 13 August and 18 September 1944 at the 3rd Belorussian Front, and from 15 January 1945 to 15 February 1945 at the 2nd Belorussian Front.[3] The Soviet Air Forces units involved were the 274th Fighter Aviation Regiment (IAP) of the 278th Fighter Aviation Division (IAD) and the 812nd IAP of the 65th IAD.[4] Twelve German aircraft were claimed by Yak-9K fighters, with an average expenditure of ten rounds per target.[1] Of these twelve German aircraft claimed by Yak-9K pilots, eight were Fw 190 and four were Bf 109G.[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.[3][6] A three-round burst, even when fired near the maximum airspeed of the Yak-9K, resulted in a noticeable loss of both airspeed and stability of the aircraft. Sometimes oil and water lines sprung leaks after the gun was fired.[3][6] Firing the NS-45 at airspeeds below 350 km/h even shook the pilot back and forth as if in an automobile suddenly decelerating and accelerating.[5]

Another issue affecting the effectiveness of the Yak-9K was that it had a poorer power to weight ratio compared to its proximate predecessor, although this was mostly due to its larger fuel tanks rather than the weight of the armament; its fuel tanks had been enlarged from the 440-liter tanks of Yak-9T to 650-liter tanks,[5] allowing it to carry an additional 153 kg of gasoline.[4] The loss of airspeed relative to the Yak-9K was about 40 km/h at 5,000 m, and climbing to this altitude took about a minute longer with the Yak-9K.[5] In an attempt to address this problem, some of the Yak-9K already in service were retrofitted with smaller 480-liter tanks.[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.[6] Ultimately, it was decided that the Yak-9K would not go into mass production.[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.[9] A total of 53 Yak-9Ks had been built by then.[3][4]

The NS-45 was also tried on an Ilyushin Il-2, with one gun mounted in each wing, but the design was not put into series production.[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. An Il-2 exemplar fitted with the new guns had been manufactured by September 10, 1943, when it was sent to the VVS NII for trials. Due to various issues which arose integrating the NS-45 gun with this aircraft, testing was delayed until February 8, 1944.[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).[10]

One of the three versions of the prototype ground attack (shturmovik) Tu-2Sh was equipped with two NS-37s and two NS-45s as frontal armament.[11] This variant was tested sometime in 1946.[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.[12] The Tu-1 was abandoned because of its unreliable engines.[3]