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| 37mm NS-37 Aircraft Gun |
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| Documents and Articles - AFVs and armament | ||||
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To the spring of 1943 the only German armor which the "IL's" could successfully combat, utilizing cannon armament, were lightly armored vehicles, halftracks, self-propelled artillery (Wespe etc...) and tank destroyers like the Marder II and III which were based on the chassis of light tanks. At this time, light Wehrmacht armor was almost non-existent on the Eastern Front. Light armor was replaced by more powerful medium and heavy tanks. In connection with these changes, upgrading of the anti-armor weaponry of Red Army aviation became a priority. By order No.3144 of 8 April 1943, plant No.30 was to begin producing a two-seat Il-2 with the AM-38F engine and two 37mm cannons 11P-37 of OKB-16 construction. Ammunition capacity was to be 50 shells to a cannon, not using HEAT shells; with a normal bombload capacity of 100kg and 200kg in overweight capacity. The amount of machine gun ammunition for the ShKAS and UBT remained the same. In the month of May, the plant was to produce 50 new Shturmoviks; 125 in June and 175 in July. In August, full scale production of all aircraft was to be with the new armament.
Ammunition of the NS-37 made up armor-piercing incendiary tracer shells BZT-37 and fragmentation-incendiary tracer shells OZT-37. Armor-piercing shells were for defeating ground targets and fragmentation shells for aerial targets. Besides that, a sub-caliber round was made for defeating armor up to a thickness of 110mm. In April, the plant produced 5 Il-2's with the NS-37 cannons, one of which was accepted for government trials at NII VVS KA on 27 May. After completing 26 flights with a total of 11 hours 35 minutes of flight time, trials ended by 22 June 1943(chief test-pilot A.I. Kabanov, chief engineer V.S. Holopov and flight spectators Major A.K. Dolgov and Engineer Major A.V. Sinelnikov). The Shturmovik that was presented for government trials differed from the basic IL-2 in that it was equipped with two NS-37 cannons with 60 shells to each cannon. Normal bomb load was 200 kg. The belt-fed NS-37 cannons allowed specialists from S.V. Ilyushin's OKB to place the cannons on the lower surface of the wing; utilizing a very simple and reliable fixture platform. The cannons were further enclosed within small aerodynamic pods; each consisting of two body shells that allowed easy access. Ammunition for the cannons was stored within the wing construction. The mass of one NS-37 with ammunition comprised 256 kg. With a flight weight of 6277 kg, a maximum speed of 387 km/h was achieved at 1320 m and 375 km/h at ground level. The practical ceiling of the aircraft never exceeded 5200 m. Besides that, it took the aircraft 3 minutes to reach an altitude of 1000 m. The maximum flight radius of the Shturmovik didn't exceed 685 km. Compared to the basic Shturmovik armed with the ShVAK or VYa, the IL-2 with the NS-37 and a bombload of 200kg became more inert. The new armament made swift turning and maneuvering very difficult.
The worsening of flight characteristics of the new Shturmovik, as with the IL-2 with the ShFK-37, was due to a large mass/wing ratio and the design of the cannon pods which lowered the aerodynamic performance of the aircraft. From an overall point of view, the IL-2 had poor balance; this indefinitely lowered cannon accuracy. This major factor was amplified by the strong recoil of the cannons during firing. According to NII VA VVS KA data (a letter of NII AV General-Major M.V. Gurevich, from 19.11.1943, to S.V. Ilyushin), the maximum strength of the recoil , present for .03 seconds, on a ground-based platform(existing technology of that time didn't allow the measuring of "the strength of recoil" in aircraft and much less in the air during firing) consisted of a considerable amount - 5500 kg, with a recoil average of 2500 kg. All of this contributed to the wide dispersal of shells during aerial firing. Proving ground trials carried out at NII AV VVS KA (this abbreviation means 'Science Lab of the Air Force of Red Army'), showed that firing of the NS-37 in the IL-2 was to be done in short controlled bursts-no more than 2-3 shells a burst. This was to be done in accordance with the fact that the cannons were not synchronized to fire together -resulting in massive jolting of the aircraft which disrupted the aircraft's line of fire. The correction of fire was possible in this case. While firing from one of the cannons, a hit was only possible with the first round, due to the fact that the aircraft turned in the direction of the firing cannon-thus making corrections would be virtually impossible. The destruction of point target such as tanks, vehicles etc... was possible only through the normal firing procedure of both cannons. In this case, hits were made on tanks in 43% of all flights; the ratio of hits to expended ammunition consisted of 2.98%. An analysis of trials results revealed that the 37mm BZT-37 shell fired from the Il-2 with the NS-37 was able to defeat every type of German light tank and armored car from a distance of 500 m at any angle of attack. This included the self-propelled gun "Wespe" and the "Marder II/III" tank destroyers. Armor such as the StuG40 assault guns, Pz III Ausf L/M and Pz IV Ausf G/H, the later StuG IV and Jgd Pz IZ/70 all had 30mm side armor which could be defeated by the BZT-37 from a distance of 500 m at an angle of 5-10 degrees and an altitude of 100 m. In this case, the attack must originate from the rear or lateral directions; directing fire along the rear deck or side of the vehicle. Shells hitting the drive wheels, sprockets and other drive components of all types of armor created considerable damage and destruction leading to immobilization of a vehicle. In the concluding reports of the government trials, special attention was paid to the fact that summer flight crews operating on the IL-2 with the NS-37 must pass a special training session in the waging of short aimed bursts against small targets(single tanks, vehicles etc...). To Factory No.30 of NKAP and OKB-16, the NKV urgently recommended the installation of a muzzle brake. Besides that, it was ordered that for the IL-2 with the NS-37, it was necessary to conduct trials with 50 shell ammunition capacities and a new bombload of 100kg. This was written in the GOKO report. In concluding, all future IL-2 variants with the NS-37 were to be equipped with these new ammunition capacities. Flight-technical data improved slightly. With a flight weight of 6160 kg, a maximum speed of 405 km/h was achieved at an altitude of 1320 m; 391 km/h at ground level. Time to reach 1000 metres: 2.2 minutes. As can be seen , designers ran into just as many problems installing the NS-37 cannons on the two-seat version of the IL-2 as with the single-seat variant. Graph 5. Limit of Through Penetration of the German armor while hitting it with BZT-37 rounds.
 On 20 July 1943 began a series of army trials of the IL-2 with the NS-37 cannons. The trials lasted until 16 December. Altogether, 96 Shturmoviks were brought to attention during the army trials(the 24th, 25th and 26th versions). Which at different times became part of the 2nd ShAK (Ground Attack Aircraft's Corps)of the 1st VA, 227th ShAD (Ground Attackers Air Division) of the 2'nd Aircraft's Army and the 219th ShAD of the 17th Aircraft's Army. Engineer-Major P.T. Abroshenko was appointed Chief Engineer of army trials from NII VVS KA. Regular pilots noted that the IL-2 with the AM-38F engine and NS-37 cannons, in comparison with the basic IL-2 with the ShVAK and VYa cannons, was very inert, was difficult to maneuver and control - especially at high speeds. The turning radius increased significantly and in pulling out of a dive at 340-360km/h a very high tension of the steering column was noticed. In gliding, the pilots were forced to hold a high speed(200-210km/h with dropped ailerons). The NS-37 spoke for themselves as a highly powerful and effective weapon. Pilots in the 568th SHAP of the 2'nd ShAK of the 1'st Aircraft's Army, operating on the IL-2 with the NS-37 from 15-26 September, destroyed 6 tanks and self-propelled guns, 99 vehicles, 10 supply columns and 6 strongpoints were suppressed. In the materials concerning army trials of the IL-2 with the NS-37 in the 17th VA, an incident concerning the destruction of a Pz.V "Panther" is brought up. For the destruction of the StuG IV Assault Gun or the Jgd Pz. IV/70 Tank Destroyer, 3 hits to the motor section were needed where the armor was only 17 mm at an angle of 20 degrees. Such was the case of the IL-2 with the NS-37, that it was capable of destroying all medium tanks and self-propelled vehicles of this period. Only the strong recoil of these cannons during firing posed difficulties in waging aimed fire at armored point targets such as tanks, SPG's... As for the experienced pilots, as was for the new recruits just coming into action. Results based on the proving grounds trials showed that the well-trained Shturmovik-pilot in all normal circumstances of attack, could attack from a 30 degree angle at a distance of 300-400m - waging fire that would assure the destruction of the Pz.IVG medium tank at .04 to .07. For a halftrack such as the Sd Kfz 251, no higher than .08 - .17. In other words, for the destruction of a solitary tank, vehicle etc... it was necessary to attack with about 15 armored IL's" In the opinions of flight crews operating on the Il-2 with the NS-37, attacking small targets with the heavier armament didn't differ much from that of the Il-2 with the smaller caliber ShVAK and VYa cannons and a normal bombload of 300-350kg PTAB. At the same time, operating the IL-2 with the NS-37 against larger targets such as ammunition dumps, multiple parked tanks, artillery and AA installations, railroad echelons, small vessels etc... could be far more effective. In the closing act of army trials of the IL-2 with the NS-37 and AM-38F, the new Shturmovik was proven to be unsatisfactory due to lower combat effectiveness. A report recommended that S.V. ILyushin, A.E. Nudelman and A.S. Suranov be asked to "install 37mm cannons with a muzzle brake and thus resubmit the Shturmovik for army trials." As insulting as it was, it was necessary to admit that the inculcation process of the new cannons amongst the troops was severely impaired by the near criminal mistake allowed by the OKB and NII AV VVS KA. The new armament was sent to the front completely unprepared for winter conditions In November-December when temperatures dropped below 10-15 degrees Celsius, air-regiments exploiting the IL-2 with the NS-37 found that a majority of the cannons jammed and refused to operate. A careful analysis showed that the NS-37's hydraulic brake was operated by a water-glycerin mixture; making the cannon inoperable for winter conditions. As always, the situation was remedied by the resourcefulness of the Russian soldier. Using the experience of pilots who used a spirit-glycerin mixture in the hydraulic brakes of the landing gear, the pilots quickly calculated the ratio of spirit to glycerin for analogous use in the cannons. The cannons' operation and recoil length was checked on the ground using the spirit-glycerin mixture. As it turned out, the cannon worked perfectly in the new parameters of 90% spirit and 10% glycerin. In essence it was almost pure spirit. After replacing the original mixture with the new spirit-glycerin mixture, the IL-2 was again able for combat flights. The use of kerosene in the NS-37 was ordered by Chief Engineer VVS KA General A.I. Repin to begin much later-in the summer of 1944.
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