Picture 1:
Early in the autumn of 1943, the Soviets were completing the first of three prototypes of their new IS-1 (IS-85) heavy tank using design experience gained from their previous KV heavy tank projects. These new IS (Iosef Stalin) prototypes were systematically demonstrated before the special commission from the Main Defense Commissariat and with the completion of general factory trials the IS design was approved for production. Although the first production vehicles mounted the 85mm gun also seen on the T-34/85 medium tank, these initial IS-1 tanks were shortly converted to carry the 122mm M1943 D-25 gun before they were provided to the tank troops. The new IS-2 tank weighed little more than its predecessor KV tank, but it had thicker and better-shaped armor that provided vastly improved protection. The overall weight was kept low by using a more compact hull and component design, as we shall see later. Once the 122mm gun was installed and series production continued, the new "Tiger Killer" was officially named the IS-2 Heavy Tank, although its weight and armor characteristics closely coincided with the German Panther medium tank. By the end of 1943, the Kirov Factory had produced a total of 102 IS-2 heavy tanks and they were used for the first time in February of 1944 at Korsun Shevkenskovsky. Although there were a number of external improvements to the IS-2 during its production and field use, there were relatively few internal changes made over the years.
Our internal exploration of the IS-2 will center around large color drawings loaned to us by Valera Potapov that appear in his excellent web site The Russian Battlefield and photographs taken by Steve Zaloga inside an IS-2m.
Picture 2:
This is the first of Valera's web site drawings, this one showing the basic exterior design of both the hull and turret for an early/mid production IS-2 (please notice that the web address on these pictures for his site has changed; the link I provided above will take you to the new site). The IS-2 hull was designed after ample combat experience with the KV tanks, and you can see that the hull actually overhangs the tracks. It is an interesting hull design in that the bow casting is welded directly to a circular casting for the base of the turret. Additional rolled armor plates are then added to form the rest of the hull sides, ending at a sloping rear plate that covers the engine and transmission. Both heavy armor castings and rolled plate are utilized in the hull, and the castings in the bow provide around 122mm (4.7in) of frontal armor. This initial bow design was based on the earlier KV-13 tank layout.
Although the first IS-2 vehicles used this curved and gently sloping front bow casting, it was later replaced in 1944 with either a new casting or a welded plate nose, both of which had a straight 60-degree slope from glacis to the top of the hull. The Uralsky Factory of Heavy Machinery (UZTM) plant made the welded noses, while factory #200 made the cast types. The IS-2 was one of the first production Soviet tanks to remove the traditional second driver/hull machine gunner from the bow of the tank, providing additional space for fuel tanks. In place of a ball mounted MG on the front plate, a DT machine gun was mounted on the right side of the hull behind the driver and up near the turret ring. It was fired via a remote control firing cable from the driver's position.
Picture 3:
The new tank design illustrates the Soviet's mid-war combat strategy reorientation from using tanks for infantry assault to tank hunting and killing machines. As a result, the second driver in the hull was deemed unnecessary and the crew was reduced from the traditional five soldiers to only four, the driver then placed in a central position in the bow. The commander is located inside the turret at the left rear, the gunner is to the left of the main gun, and the loader is to the right. Both the gunner and loader are provided with over-head periscopes and the commander has a non-rotating turret cupola incorporating vision blocks that provided a 360-degree field of view. He also has a rotating periscope in his cupola hatch. A round roof hatch that is flush with the turret roof is provided for the loader on his side of the turret.
Initially, the 122mm L/43 gun mounted in the cast turret retained its original interrupted screw breech, showing its ancestry from the already proven D-19 field gun. But the screw field gun breech was replaced (by early 1944) with a horizontally sliding block, semi-automatic type, and of course the recoil cylinders and elevating mechanisms were altered from the field gun to fit into a turret. Because the 122mm ammunition rounds were so huge, they were provided in separate pieces, a projectile and a charge cartridge, but even so only 48 complete rounds could be stored inside the tank. Although a number of ready rounds were strapped into easily reached racks in the turret, most of the ammo was stored in sheet metal boxes down on the hull floor and, as we have seen in the T-34/76, these boxes were often covered with rubber floor mats. There was no turret basket in the IS-2; the turret crew seats were either suspended from the turret and rotated along with it (commander's) or the seats were supported on tubes that rose from the center of the floor and also rotated with the turret (gunner and loader).
Picture 4:
By the time the IS tanks were being manufactured, the Soviets had plenty of technical experience with casting large pieces of armor, and the IS-2 turret became one of the biggest castings they manufactured during the war. Although Western writers have tended to criticize the coarse standard of Soviet armor finish, the urgency of tank manufacture in 1943 did not warrant lavishing extra time and energy on unnecessary refinements. Over the course of its production, the turret was gradually changed. The early IS-2 tanks that were manufactured in 1943 were originally designed to have installed a D-5T 85mm gun in their turrets, and they had a narrow opening for the telescopic sight just to the left of the gun. When the 122mm D-25T gun was placed inside these same turrets, it was very hard for the gunner to use his telescopic sight, as it was so close to the gun. So, in mid-1944 a new turret with a larger sight opening that was also shifted slightly to the left was produced. Also at this time the thickness of the turret's mantlet was increased, along with the lower hull sides. The new turret also moved the commander's cupola slightly to the left and the gunner's PT4-17 periscopic sight in the turret roof was changed over to a Mk.4 type. About this time a Model 1938 12.7mm DShK anti-aircraft machine gun was installed outside on the commander's cupola to provide some protection from strafing German aircraft.
This drawing shows the general arrangement of projectile storage in the turret bustle, where many AP-T and HE-Frag projectiles were stowed. There are also a couple of brass charge cartridges strapped down horizontally on the right turret lip, as well as a pistol port and storage for flair pistol rounds up on the right turret wall. Down on the right track sponson are additional horizontally stowed charges while the seat for the commander at the rear of the turret ring is shown folded up on the turret lip under the 7.62mm DT machine gun that was initially mounted in the bustle. The gunner and loader's seats are supported on hollow tubes that rise from the center of the floor and rotate with it. The V-2IS, four-stroke, V type, 12-cylinder engine is located in the rear of the hull, and in this drawing some of the firewall separating the fighting compartment from the engine compartment is visible. The diesel engine produced around 520hp to push the tank a maximum of 23mph on the road and roughly 18mph cross country. Maximum range with the internal fuel was 150mi.
Picture 5:
Stripping away the rest of the turret and some additional portions of the hull provides this view of additional internal components of the IS-2. In the turret area you can now see the support tubes for the gunner and loader's seats, as well as a part of a third tube (conduit) carrying electrical and radio wires up to the turret equipment. Down below the seats are some of the sheet metal storage boxes for shell charges, and a starting crank handle is visible on the firewall at the rear. Up forward is the central driver's position, flanked by the two large diesel fuel tanks, although additional fuel tanks are located in the rear on either side of the engine. Total fuel inside the tank was around 137gals, but additional fuel and oil drum tanks were normally lashed to the sides of the engine compartment. The oil drums were particularly important as the V-2 engine used huge quantities of oil.
Along both hull walls, just behind the driver, are two sets of vertical storage racks for more brass charge cartridges, although only the rack on the right side of the hull is drawn here. As we have found in many Soviet WWII tanks, the V-2 diesel engine could be started with compressed air in very cold weather, and the air storage cylinders are located up in front of the driver. A DT machine gun is shown located in the right forward hull, but back directly under the turret ring. I have to admit that I had never noticed this weapon before in photographs of the IS-2, but as I researched images for these pages I found the MG mounting on many early IS-2 tanks. Curious.
Picture 6:
Now the engine and rear mounted transmission are visible, as well as a number of the yellow compressed air tubes and other control lines from the driver's area to the rear of the hull. The engine setup is very similar to what we have seen in the medium tank T-34, in that the engine is attached directly to the multiple dry main clutch, which is then attached to a scirroco cooling fan, which then attaches directly to the mechanical gearbox and differential. The gearbox provides eight forward gears and two reverse. The water radiator originally designed for the KV-13 predecessor of the IS-2 is an interesting design. Also used in the IS-2 tanks, it was in the shape of a horseshoe and efficiently covered the sides and top of the large cooling fan. The steering brakes and final drives are mounted on either side of the transmission, and the rear mounted drive sprockets are attached to the final drives. Also visible here are the torsion bars of the suspension, again this was one of the first Soviet tanks to utilize the German developed torsion bar suspension which was also to be seen in other Allied tanks by the end of the war. You see the torsion bars running in pairs across the hull floor because each bar enters the hull from a road wheel station and then crosses the hull to attach to the opposite wall.
Picture 7:
Now, through the courtesy of Steve Zaloga, we will slide down into an IS-2m that he photographed while at the Duxford Museum in England. These photos were taken with a very wide-angle lens, which allows us to view a good portion of the interior components but also slightly distorts the edges of the photographs somewhat. In this case, we are at the rear of the fighting compartment, just in front of the firewall, looking forward toward the central driver's position. The IS-2m, or IS-2 Model 1944, was the vehicle's name given when the front bow armor was changed to a straight slopping plate, the gunner's PT-4-17 periscope was replaced with the Mk.4, the wider turret mantlet was substituted, and the 12.7mm DShK heavy machine gun was mounted on the turret cupola. Our first picture above shows an IS-2m although the DShK is not mounted.
Directly in front of us is the combination seat support and electrical collective ring, the gunner and loader's seats supported on the two tubes painted white with the hinges at the bottom, allowing them to swing under the gun breech and to be out of the way when necessary. The third tube contains wires for the radio and electrical components in the turret, the conduit rising from the collective up to the turret lip near the gun mount. On the floor surrounding the tube supports and collective are a number of stowage boxes for 122mm ammo. Also down there are two darker colored battery boxes, one at either side of the floor, near the sponson walls. Just forward of the battery boxes are the vertical brackets for storing charge cartridges that we saw in earlier drawings, there were approximately five charges in each rack.
The large boxes on either side of the driver's seat are the diesel fuel tanks we saw in a previous drawing, and the steering levers and gearshift are also visible near his seat. The driver has three viewing devices, two rotating periscopes at either side of his position, and one episcope mounted directly on the front armor plate in front of him. As far as I can tell, the driver has no exit at his position so he must crawl back into the fighting compartment to enter and leave the vehicle via the turret. The huge underside of the 122mm breech ring is at the top of the image with some of the traverse gearing visible to either side. To the right and just below the turret ring you can see the black mounting ring for the forward facing DT MG, but the MG is missing.
Picture 8:
Stefan Kotsch sent us a few drawings of Soviet machine guns, this one illustrating the 7.62mm DT 1929, used in the IS-2 as the hull MG as well as the coax. Notice that unlike the infantry version (known as the DP-- the 'T' in DT stands for tank), the DT MG has a retractable metal stock in place of the wooden one, and also now has a wooden pistol grip. The drum magazine was typically used in Soviet tanks and the drum held 60 rounds in two layers, therefore making it thicker than the drum used with the DP version. Normally, a separate optical sight (1 and 2) was mounted when the DT MG was installed inside a tank.
Picture 9:
Here is an enlargement of the previous photo emphasizing the driver's area in the bow. Steering was via a regenerative two-stage system with skid turns, and the levers could be locked in any position. Full back lock on both levers effectively placed the brakes into the parking position. The gearshift lever is to the driver's right and is mechanically connected to the synchromesh transmission (or manual gearbox, sources vary on this point) at the rear of the tank. Above the gearshift is the driver's primary instrument panel and electrical switch/fuse box, and a radio connect box for him is also visible. Notice that you can now see the ends of two dark compressed air cylinders under the forward episcope. And although you can't see them from this angle due blockage by the driver's seat back, there are traditional brake and clutch pedals down on the floor in front of the seat. Also up there is a back-up hand pump for the compressed air cylinders.
Picture 10:
This is the view looking forward to the gunner's seat from the commander's position-- the commander's cupola is visible directly above us. The typical 10RK radio transceiver and intercom system is to our left, and a number of racks for 7.62mm DT MG ammo drums can be seen down on the sponson to our left and on the other side of the radio. Directly forward from our position is the dark gunner's seat with his elevation and traverse hand wheels, and the D-25T gun breech is visible to our right. The commander's cupola is non-rotating, but the six vision blocks are spaced so an almost complete 360degree view is provided. There are protective face pads around each cupola block and shattered glass blocks can be easily replaced by opening the latch under the frame. Normally, a rotating periscope is also mounted in the center of the cupola hatch over our heads. On the turret ceiling, just forward of the cupola, is a Soviet interior dome light, typically with a blue lens installed.
Total production of the IS-2 tank amounted to around 2,250 vehicles by the end of the war. Of these, approximately 250 were reported to have been constructed in the first quarter of 1944, 525 in the second quarter, 725 in the third, and 750 in the last. When the first IS-2 tanks rolled off the factory floor and out the door, they were placed in special new units designated as separate Guards heavy tank regiments (OGTTP). These units typically had 21 IS-2 tanks divided into four companies with five tanks each. The Guards units were also known as "break through" regiments indicating their powerful offensive design.
Picture 11:
Turret traverse was either manually by hand or powered with an electric motor, the hand wheel can be seen on the left. Gun elevation was via the darker handle you see in the center of the enlarged photo and it was manual only. There was no stabilization on these guns and the laying equipment was fairly simple and simple to operate and maintain.
Visible down on the floor between the elevation hand wheel and the gunner's seat is this side's vertical storage rack for 122mm charges that we saw earlier, and also a storage rack for MG ammo drums is at the lower left. Up in the turret we can just see that storage rack for additional MG ammo drums seen earlier, along with the gunner's radio connection box for his headset and microphone. The periscope in the roof is the later Mk.4 type while the 10-T-17 telescopic sight is directly in front of us and has the forehead pad adjusted to view through the sighting ocular with our left eye.
The over-head dome light now dominates the top of the photo, and some of the left side of the huge green breech ring is visible to our right. Laying on top of the flat ring is the black breech actuating handle, and if you look carefully just forward of the handle you can barely see the two recoil cylinders laying on top of the gun tube. The gun can be fired either electrically via the thumb button on the traverse wheel, or mechanically by the lanyard you see hanging in front of the gun shield, just to the lower right of the elevation hand wheel. Elevation of the big gun was from -3 to +20 degrees.
Picture 12:
Another of Steve Zaloga's photos illustrates some of the equipment on the loader's side of the turret in this preserved IS-2m. The black electric turret ventilator is at the upper left over the gun, and one of the recoil cylinders is visible up near the gun mount/mantlet. To the right of the gun tube is the mount for the 7.62mm DT coaxial MG, which is not mounted in this vehicle. The loader's Mk.4 roof periscope is to the right of the ventilator and further right is another interior dome light. Forward of the periscope is another vertical rack for four DT MG ammo drums and below the rack is the electric motor and gearing for powered traverse. Notice the thin drive shaft arriving from the manual hand wheel on the other side of the weapon and here entering the gearbox in front of us. The small radio connect box on the turret wall under the dome light is for the loader. At the end of this wire is the plug that attaches to his helmet lead, and the plug is neatly tucked into the leather pouch you see on the turret wall to the right of the control box. Down on the hull floor are more of those green 122mm ammo boxes and the vertical rack for a few charge cartridges on this side of the forward hull are seen under the turret traverse motor.
When the Soviets tested their D-25T gun against a captured Panther tank, the 122mm gun manufactured at factory #9 easily "penetrated" the Panther's frontal armor at 2,500 meters. The Soviet report states that the gun's ballistic characteristics were identical to those of the A-19 122mm field gun, the D-2 122mm gun (factory #9), and the S-4 gun (Central Artillery Design Bureau), giving it a muzzle velocity of 780-790m/s with a 25kg projectile. I suspect the Panther in question was not "penetrated" by an AP-T round, as it did not have the kinetic energy at this velocity and range, but instead the Panther probably had its armor shattered by a HE-Frag projectile. Maximum range for the D-25T weapon was stated to be over 3,000 meters, but of course accuracy at that distance was totally nonexistent due to the variations in ammo and gun barrels, and the lack of sufficiently precise Soviet sighting equipment. Most records indicate that tank duels took place well under 1000 meters in WWII, and at that range the D-25T's AP-T probably would indeed penetrate the Panther's front plate, particularly those made from 1944 on with homogenous armor.
Picture 13:
This interior picture shows the rear of the turret with racks for both AP and HE projectiles. The typical AP-T projectile used in the IS-2 was the BR-471B and the HE-Frag was OF-471N. Since the AP projectile was shorter it was stored in the rack at the right and the HE in the left rack. As far as the charge cartridges are concerned, both types were made from brass and were the same general shape with little of any narrowing near the cardboard plug at the end. But the charge casings for the armor-piercing BR-471 projectile had a red identification band around the case near the black lettering. Notice how the upper bracket supports for the projectiles may be adjusted in height along the vertical support rods. The recoil guard for the 122mm gun almost touches the rear of the turret lip and there is a secondary guard mounted on its left rear corner to protect the commander over in his position. The recoil guard obscures the commander's seat. Back further in the commander's corner of the turret is the rear DT MG mount and the commander's radio connect and control boxes are also seen mounted to the wall. Up in the cupola you can just see the bottom of the periscope mounted in the hatch. I believe that that is a padded black canvas Soviet tanker's helmet laying on the projectile rack, complete with the radio connect plug hanging down.
Picture 14:
If we stand up in the commander's position with the hatch open, we would have access to the 12.7mm MG up on his cupola. This is another drawing sent to us by Stefan Kotsch, this one showing how the MG was mounted and the anti-aircraft sight was used at the end of the war, and beyond. The DShK was the standard Soviet heavy machine gun for most of the war, used as the standard infantry gun as well as secondary armament on their larger armored vehicles. The gun was a joint design project by both Degtyarev and Shpagin. The feed mechanism was very unique-- a rotary block which was protected by a steel stamping, was positioned above the breech mechanism. When the cartridges were stripped from the links in the belt, they were revolved around the block and inserted into the chamber.
Picture 15:
The external appearance of the DShK resembled the DS machine gun, with spade grips, trigger mounted on the back plate, and barrel with cooling fins and large muzzle brake welded to the end of the muzzle. The anti-aircraft sights replaced the standard leaf rear sight when mounted on tanks, the AA sight being either the M1938 or M1941 type. They were both said to be suitable for firing at rapidly moving surface and air targets.
By 1943, the Soviet DShK had been in wide use for some time, and there were complaints of breakages and feed problems coming in from the using troops. To help remedy the problems, the revolving feed mechanism was removed and a simpler
setup, using a claw to pull the cartridge out of the belt and present it in front of the bolt, was installed. Some other parts were also strengthened and simplified. The new model became the DShKM (sometimes with "38/46" added behind the M), the M referring to "Modernized". In this guise, the trusty MG served on with Soviet forces well after WWII, with many still in service today.
Picture 16:
Two IS-2m tanks stand ready as their crews listen to instructions from a Soviet officer. All the tankers seem to be wearing the late war, black leather, 3/4 length jacket over their khaki coveralls. The photo appears to have been taken in Berlin in 1945 at the end of hostilities, and the white stripe on the farthest IS-2m turret was an Allied identification marking introduced at this time to help Allied aircraft avoid attacking unfamiliar Red Army tank formations. Our Picture 1 is taken in a similar setting but in a more severely damaged section of the city.
Again, I would like to thank Valera Potapov of The Russian Battlefield for the use of his drawings of the interior of the IS-2, as well as Steve Zaloga for loaning us his interior photographs of the IS-2m. Steve's images can also be seen in a number of his own publications on Soviet/Russian armor, including the New Vanguard series of Osprey Publishing's "IS-2 Heavy Tank 1944-1973" and Concord Publications Company's "Stalin's Heavy Tanks 1941-1945, The KV and IS Heavy Tanks". Also I would like to thank Stefan Kotsch for the machine gun sketches. We have plenty of room for additional images and reference information about the interior of the IS-2 in these pages. Please feel free to contact me if you care to contribute.
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