"Experimental work on heavy SPGs.
The creation of heavy artillery SPGs follows the goal of increasing the firepower of tanks. Since placing 152 mm guns in the turrets of existing tanks was not possible, it was deemed reasonable to place these artillery systems in immobile fighting compartments. In order to preserve the production numbers of SPGs at tank factories, the overall component layout was preserved. As experience showed, unification of tanks and SPGs was very effective. It was possible to set up mass production in very short amounts of time with minimal decrease in production numbers. In order to fill the Red Army's need for new heavy SPGs, the following work was done.
1. On the ISU-152 SPG.
According to GOKO decree, in December-January of 1942-1943, the SU-152 was designed and built by the Kirov factory. The SU-152 SPG consists of a 152 mm gun-howitzer on a KV-1S chassis. The SPG was tested in January-February of 1943. GOKO decree #2883 on February 14th, 1943 adopted the vehicle into the Red Army.
Mass production SU-152 produced by the Kirov factory
Experimental ISU-152 SPG produced by factory #100
- Combat mass: 45.5-46 tons
- Crew: 5
- Front armour: 60-100 mm
- Side and rear armour: 60 mm
- Armament: 152 mm ML-20 gun-howitzer
- Muzzle velocity: 600 m/s
- Horizontal traverse: 10 degrees
- Vertical traverse: -3 to +20 degrees
- 152 mm shells: 20
- Average highway speed: 23.4 kph
- Maximum speed: 37.5 kph
- Average off-road speed: 18.2 kph
- Engine: V2-IS
- Maximum engine power at 2000 RPM: 520 hp
- Fuel type: diesel
- Fuel capacity: 500 L
The experimental ISU-152 SPG passed trials and was recommended for adoption by the Red Army. The ISU-152 was adopted into the Red Army by GOKO decree 4504ss on November 6th, 1943, and is still produced at the Kirov factory.
Compared to the SU-152, the ISU-152 has stronger armour and a more robust transmission, engine, and suspension design. The armament was unchanged, as the ML-20 was powerful enough for any application. The ammunition rack, sights, observation devices, among other components, were also improved.
Engineer-Major comrade Rabtsev worked admirably in designing the ISU-152 SPG. As a part of a commission led by Engineer-Colonel comrade Demyanenko, comrade Rabtsev corrected several defects in the ML-20 gun mount.
2. On the ISU-122 and ISU-122S SPGs.
An experimental prototype of a heavy SPG with a 122 mm A-19 gun instead of the ML-20 was built by factory #100 in December of 1943. The work was conducted in agreement with USA GBTU to increase the anti-tank power of the SPG. This was achieved by replacing the 152 mm gun barrel with the 122 mm A-19 barrel. The gun mantlet and ammunition rack were changed, without alterations to any other components of the production SPG.
With the installation of a 122 mm gun, the following was achieved:
- High penetration. 122 mm shells with a muzzle velocity of 800 m/s penetrated thick armour, which was necessary in battle with German tanks and SPGs.
- High rate of fire and precision. The rate of fire of the A-19 was twice as high as the rate of fire of the ML-20.
- Increase of the ammunition rack from 20 shells to 30 shells.
- Reduction of the combat weight due to a lighter gun system.
Trials of the ISU-122 were conducted at the Gorohovets proving grounds from December 24th to December 31st, 1943 over 463 shots by a commission led by Major-General of the tank engineering service comrade Alymov. The SPG passed trials. Based on this, the ISU-122 was recommended for service in the Red Army. By GOKO decree #5378 on March 12th, 1944, it was put into mass production at the Kirov factory.
As a result of the 122 mm D-25 gun with identical ballistics entering production at factory #100, the factory was tasked to design an SPG that uses the D-25 gun. In April 1944, the ISU-122S SPG was built. The ISU-122S is a further modernization of the ISU-122 SPG that increases rate of fire. The D-25 is designed as a tank gun, and its recoil mechanisms and breech are more compact than on the A-19. As a result of this, the crew was more comfortably placed in the fighting compartment. The shorter recoil and sliding breech (the A-19 had a screw breech) increased the rte of fire (from 2.5 RPM on the A-19 to 6 on the D-25). The unification of tank and SPG guns was also important.
The experimental ISU-122S prototype was tested at the Gorohovets proving grounds from June 2nd to June 7th, 1944, by a commission headed by Engineer-Colonel comrade Kupriyanov over 446 shots and 192 km. Tests were conducted carefully and with a high level of mastery. Due to superior qualities of the ISU-122S SPG over the ISU-122, it was recommended for adoption into the Red Army. GOKO decree #6430 on August 22nd, 1944 adopted the ISU-122S for service. The ISU-122S remains in production at the Kirov factory to this day. It is important to point out that both the ISU-122 and ISU-122S are still in production. This is due to the fact that D-25 production is insufficient to cover demand.
- Combat mass: 45.5-46 tons
- Crew: 5
- Front armour: 60-100 mm
- Side and rear armour: 60 mm
- Armament: 122 mm A-19 gun
- Muzzle velocity: 781 m/s
- Horizontal traverse: 10 degrees
- Vertical traverse: -3 to +20 degrees
- 122 mm shells: 30
- Maximum speed: 37.5 kph
- Average highway speed: 23.5 kph
- Average off-road speed: 18.2 kph
- Engine: V2-IS
- Maximum engine power at 2000 RPM: 520 hp
- Fuel type: diesel
- Fuel capacity: 500 L
- Combat mass: 44.5-45 tons
- Crew: 5
- Front armour: 60-100 mm
- Side and rear armour: 60 mm
- Armament: 122 mm D-25S gun
- Muzzle velocity: 781 m/s
- Horizontal traverse: 11 degrees
- Vertical traverse: -2 to +20 degrees
- 122 mm shells: 30
- Maximum speed: 37.5 kph
- Average highway speed: 25 kph
- Average off-road speed: 18.1 kph
- Engine: V2-IS
- Maximum engine power at 2000 RPM: 520 hp
- Fuel type: diesel
- Fuel capacity: 500 L
3. On the ISU-122BM and ISU-130 SPGs.
In order to further improve the armament of heavy SPGs, the government decided to produce new 122 mm guns with a muzzle velocity of 1100 m/s and 130 mm guns with a muzzle velocity of 900 m/s. According to GOKO decree #4851 from December 27th, 1943, factory #100 produced three experimental prototypes: two ISU-122BMs and one ISU-130, equipping production SPGs with these guns.
The ISU-122BM SPGs were built wit a 122 mm BL-9 gun designed by OKB-172, and one with a 122 mm S-26-1 gun designed by TsAKB. The BL-9 and S-26-1 have identical ballistics and differ in component design. The muzzle velocity of these guns is over 1000 m/s, and 200 m/s higher than the D-25. The increase of muzzle velocity increased the penetrative power of the guns.
The experimental SPGs were late due to delays in producing the guns. The ISU-122BM with a BL-9 gun was delivered for trials on July 9th, 1944. The second, with the S-26-1 gun, was delivered to trials on November 15th, 1944, instead of April 1st, 1944, the term stated in the GOKO decree.
The ISU-130 was produced and delivered for trials on November 25th, 1944, instead of April 5th, as per decree. The prototype used a 130 mm S-26 gun designed by the TsAKB, based on the B-13 naval gun.
Trials of the three SPGs were split into three stages.
- First stage: preliminary artillery trials at GANIOP in Leningrad.
- Second stage: proving grounds gunnery and mobility trials. Gunnery trials are to be held after the guns pass preliminary trials.
Trials results:
The ISU-122BM with a 122 mm BL-9 gun designed by OKB-172 failed trials due to insufficient robustness of the barrel (August, 1944). A decision was made to improve the barrel and test the gun again. A new barrel was ready by February of 194. The delay with the new barrel and the S-26-1 barrel was due to the fact that NKV only produced one of each barrel. After their breakage, a lot of time was needed to make new ones.
Despite the demands of the Military Council of the Armoured an Motorized Forces of the Red Army to produce backup barrels, NKV did not do so, and did not take into practice producing experimental guns with large muzzle velocities. Delays were also caused by factories #172 and #232, which delivered poor quality barrels.
The BL-9 passed preliminary trials in 1945, from April 5th to May 30th. The ISU-122BM is currently undergoing trials in parallel with the other ISU-122BM SPG.
The ISU-122BM SPG with the S-26-1 gun failed November trials. Its barrel was also insufficiently robust. Correction of the gun took a long time, for the same reasons as above. Only by June 1945 was a new barrel installed on the SPG to make it ready to resume trials. Which of these SPGs is superior and which will be mass produced will be discovered in the near future.
With an SPG armed with a similar gun, the Red Army will gain a new powerful method to combat even heavier enemy tanks and SPGs.
Experimental prototype of the ISU-122BM SPG built at factory #100
- Combat mass: ~47 tons
- Crew: 5
- Front armour: 60-100 mm
- Side and rear armour: 60 mm
- Armament: 122 mm BL-9 or S-26-1 gun
- Muzzle velocity: 1000 m/s
- Horizontal traverse: 10 degrees
- Vertical traverse: -1 to +18 degrees 40 minutes
- 122 mm shells: 20
- Maximum speed: ~37.5 kph
- Average highway speed: 23.4 kph
- Average off-road speed: 18.2 kph
- Engine: V2-IS
- Maximum engine power at 2000 RPM: 520 hp
- Fuel type: diesel
- Fuel capacity: 500 L
The ISU-130 SPG underwent artillery trials at the Leningrad proving grounds twice, once from November 24th to December 8th, 1944, and once from December 14th to December 31st, 1944. 663 shots were fired in total (1st stage: 359 shells, 2nd stage: 304 shells). After defects found in the second stage, the ISU-130 was returned to TsAKB to be corrected for further trials.
Despite numerous demands from GBTU, the correction took until May of 1945. Currently (June 1945) it is undergoing mobility and additional gunnery trials. The ISU-130's gun is a naval caliber gun, and has never before been used by the Red Army. However, considering the positive qualities of the 130 mm gun, it may be worthwhile to introduce a new shell caliber.
Experimental prototype of the ISU-130 with a 130 mm S-26 gun
- Combat mass: ~47 tons
- Crew: 5
- Front armour: 60-100 mm
- Side and rear armour: 60 mm
- Armament: 130 mm S-26
- Muzzle velocity: 900 m/s
- Horizontal traverse: 7 degrees 50 minutes
- Vertical traverse: +16 degrees 30 minutes
- 130 mm shells: 20
- Maximum speed: 37.5 kph
- Average highway speed: 23.4 kph
- Average off-road speed: 18.2 kph
- Engine: V2-IS
- Maximum engine power at 2000 RPM: 520 hp
- Fuel type: diesel
- Fuel capacity: 500 L
4. On the ISU-152BM SPG.
The experimental ISU-152BM prototype was produced by factory #100 on its own initiative in April of 1944. This prototype used the BL-8 152 mm gun at first, then the BL-10 gun, produced by factory #172. These guns were installed in a production ISU SPG.
The BL-8 and BL-10 guns have the same muzzle velocity of about 850 m/s and identical ballistics. They differ in the breech type. The BL-8 has a screw breech, while the BL-10 has a semi-automatic sliding breech.
In July of 1944, the BL-8 gun was tested on the Leningrad artillery proving grounds over the span of 501 shots. Trials showed flaws in the gun's design. As a result of July trials, a new gun was built, indexed BL-10. In the end of August of 1944, the ISU-152BM SPG with a BL-10 gun was delivered to the Leningrad artillery proving grounds for trials. However, trials were delayed due to a delay in procuring the new type of AP shell.
In December of 1944, the BL-10 was trialled, but failed trials due to insufficient robustness of the barrel, and was sent back for corrections. Production of a new barrel was delayed due to defects at factory #172. A new gun barrel was only built and produced by July of 1945.
With the successful correction of this gun's defects, the Red Army will receive a new, more powerful, artillery system that can defeat any known or potentially built tanks and SPGs of the enemy. Aside from its AP performance, the gun has good HE performance against enemy artillery and other targets.
The SPG may be further improved by reducing the overhang of the barrel by moving the fighting compartment backward and widening the fighting compartment.
Experimental prototype of the ISU-152BM SPG built at factory #100
- Combat mass: ~47 tons
- Crew: 5
- Front armour: 60-100 mm
- Side and rear armour: 60 mm
- Armament: 152 mm BL-10
- Muzzle velocity: 850 m/s
- Horizontal traverse: 8 degrees
- Vertical traverse: -3 degrees to +18 degrees
- 152 mm shells: 21
- Maximum speed: 30-34 kph
- Average highway speed: 23-25 kph
- Average off-road speed: 18 kph
- Engine: V2-IS
- Maximum engine power at 2000 RPM: 520 hp
- Fuel capacity: 500 L
Experimental prototype of the IS-3 based heavy SPG produced at the Kirov factory
- Combat mass: ~47 tons
- Crew: 5
- Front armour: 120 mm
- Side armour: 90 mm
- Rear armour: 60 mm
- Armament: Modernized 152 mm ML-20SM gun-howitzer
- Horizontal traverse: 10 degrees
- Vertical traverse: -2 degrees to +18 degrees
- 152 mm shells: 20
- Maximum speed (calculated): 37 kph
- Engine: V2-IISI
- Maximum engine power: 520 hp
- Fuel type: diesel
- Fuel capacity: 650 L"
I thought the ISUs had 75-90 mm armor on their sides, why did the document state that they had only 60 mm?
ReplyDeleteIt says "side and rear". You are right that only the rear superstructure is 60mm.
ReplyDelete