Purpose of the visit: to receive information on the combat use of heavy IS-122 tanks.
Time in the regiment: from February 5th, 1944 to March 27th, 1944
The tanks were received by the regiment on January 30th, 1944. All tanks were built in December of 1943. When delivered, the tanks' engines worked between 17 and 23 hours.
From February 5th to February 12th, company and regiment level driving and shooting training was conducted at the Tula tank camp. After the end of tactical training, tanks spent 35-38 engine hours in total.
On February 13th, the regiment was sent to the 1st Ukrainian Front.
On February 17th, the regiment was delivered to Belaya Tserkof.
From February 17th to 22nd, the tanks were stationed at Belaya Tserkof in full combat readiness.
The engines were maintained in a state ready to start in winter conditions using antifreeze and kerosene burners. It was established that at external temperatures of -10 degrees, and non-stop running of kerosene burners, the engines must be started to warm up every 10-12 hours. It takes 15-20 minutes to warm the engine.
On February 22nd, the regiment was loaded into a train again, and got off on February 26th at Polonnaya station. After delivery, the tanks made a 24 km march to Varvarka village. 20 tanks were in working condition, one had a bent spring in the inertial starter and had to be started up while being towed.
From March 4th, the start of the offensive on the 1st Ukrainian Front, the regiment was on a non-stop march, only stalling in regions where enemy resistance was heavy.
From March 4th to March 25th, the tanks travelled about 250 km. The tanks expended 120-130 engine hours. The ratio of time to distance is explained by the difficult road conditions in which the regiment had to march. Tanks travelled mostly on destroyed dirt roads, which were covered in mud 450-500 mm deep. Also, the tanks had to navigate a number of small water hazards and swamps.
On March 4th, tank #3123 fell through a bridge at Hrabuzna village. Evacuation of the tank was not performed until March 17-18th. Due to difficult road conditions, tanks travelled in 2nd or 3rd gear. One refill of fuel lasted 50-60 km.
From March 4th to March 25th, the regiment lost 10 tanks, two burned up at Keraimovka on March 8th from shell hits, and 5 tanks burned up at Redvintsy from shell hits, as well as 2 tanks drowned in the river and were blown up, and one was blown up by the crew when its suspension was damaged.
From March 4th to March 25th, 4 tanks had their suspensions damaged, one tank lost its idler, another the drive wheel, two tanks lost return idlers.
From the moment of the tanks' arrival to March 25th, 94 technical defects were discovered in the tanks, of them:
- Engine group: 24
- Transmission: 20
- Suspension: 10
- Electrical equipment: 12
- Armament: 13
- Control devices: 12
- Hull: 3
Out of the 24 engine group defects, 17 were related to the inertial starter. Out of the 13 armament defects, 13 were related to the electrical and mechanical firing mechanisms for the machineguns or gun. In order to correct the defects, the following repairs were conducted:
- Immediate repairs: 70
- Medium repairs: 23
The time required to correct these defects is recorded in attachment #1. Tank #3123 required an engine replacement and was sent to Kiev.
Based on observations of IS-122 tanks, the analysis of technical defects, and reviews from crews and commanders, it is possible to evaluate the performance of the tank, its reliability, and crew comfort.
- The maneuverability of the IS-122 tank on the battlefield is superior to that of the KV-1S tank, and no poorer than the T-34 tank. It is easier to drive the IS-122 tank than a KV-1S or T-34.
- Armament: the presence of a 122 mm gun gives the tank a firepower advantage over all enemy tanks. There were cases when enemy tanks (Panthers) were destroyed and burned from 2000 meters, with only one shell. There was a case when a Panther tank was destroyed and burned from one HE shell fired from the D-25 gun at 1200 meters.
Drawbacks of the armament and fighting compartment.
- Low rate of fire. For every 1-1.5 shots, the enemy Tiger or Panther can fire 3-4 times.
- The large cloud of smoke after firing makes it difficult to observe the battlefield, aim, or hide the tank.
- The loader's position is cramped when the screw breech is open. This can be solved by a sliding breech. The commander's position is cramped due to the brass catcher. This can be resolved by moving the commander's seat and cupola left by 200 mm.
- There was one case of a broken firing pin due to poor thermal conditioning.
- The ammunition rack should be expanded to 35-38 shells. At the same time, it is necessary to move the propellant from the sides of the turret, as when the turret is penetrated from the side, the ammunition can detonate, and then the tank will burn. The turret bustle should be modified to hold amour piercing shells.
- The 10T-17 sight is not good enough to fire at long distances. It should be replaced with a refracting sight with a larger view angle and magnification.
- The IS-122 tank has no AA armament. It is necessary to install a high caliber AA machinegun.
- Turret and hull: there is not enough data to comment on the quality of armour protection of the IS-122 tank. Poor quality of welding seams should be noted. Tank #31224 had a crack 200 mm by 5 mm in the joint between the left side and turret platform in the transmission compartment. Tank #3128 had a crack in the same place, but on the right side, 150 mm by 5 mm. The turret casting quality is poor, cracks form on impact.
The air exhaust grilles do not protect the water radiator from aircraft fire. It is necessary to alter their design.
The towing hook clasp is weak, and broke on almost all tanks during towing.
The hatch torsion bars have a high twist angle and break often.
- Engine group: aside from the inertial starter, the engine group works reliably. By March 25th, engines worked for 120-130 hours. Oil pressure is normal. All regulators perform perfectly on all engines. Tank #31230 had the 8th bearing of the crankshaft deform from heat, the cause has not been established. The main defects of the electro-inertial starter are:
- Starter button contacts burn out.
- Electric motor brushes burn out.
- Electric motor burns out.
- Friction clutch slips due to insufficiently tightened pressure disk.
- Spring bends.
- The starter gear breaks.
- The insulation on the wiring to the starter gear relay burns.
- The stopper nut on the starter gear ball bearing is insufficiently tightened, and balls fall out.
It is necessary to:
- Increase engine power.
- Increase the robustness of the spring by improving material and processing.
- Improve the nut stopper of the starter gear ball bearing, or redesign the ball bearing.
- Redesign the starter button, make it more convenient to take apart, and also reinforce the contacts.
- Increase the tightening moment of the friction clutch, improve the pressure disk stopper.
Note that it is difficult to spin the starter manually when starting in winter conditions.
- The main friction clutch is reliable. 7 cases of scorching happened due to inexperience of the drivers and poor control over the regulation of the clutch, which will lead to scorching in difficult road conditions.
- Gearbox: this component is reliable. The multiplier shaft carriage had some cracked teeth, which led to parts of the teeth jamming the carriage on tanks #31225 and #31234.The insufficient attachment of the gearbox balancers led to the holder breaking (in 5 cases). On two tanks, #31227 and #31213, this caused two gears to be selected simultaneously, and gear teeth breaking.
Currently, Kirov factory produces a balancer holder that is modified to not permit this to happen.
- Planetary turning mechanisms: ball bearings broke in two cases:
- Tank #31227: the ball bearings did not have rubber rings.
- Tank #31220: the ball bearing type was not known.
Tank #31228 had the clutch release ball bearing break.
- Final drives: the final drives worked reliably on all tanks and had no defects.
- Suspension: the track pin life is insufficient.
- After 100-200 km, the tracks sag enough to need to remove one track link. After 300-350 km, due to the tracks being worn, there were cases when tracks tore at the eye.
- The return idler carriers are weak, there were cases when bolts were torn off.
- The stopper of the tightening mechanism is insufficiently robust. There were cases where the tracks would loosen or the stopped would be torn off.
- Mudflaps and their holders need to be reinforced.
- The idler ball bearing on tanks #31224 and #31235 was destroyed.
- Controls: the regulation of the main friction clutch and gearbox were stable over the observed period. All tanks came from the factory with an uncalibrated turning mechanism. The length of the springs was not in accordance with the technical specification (470-480 mm instead of 530-540 mm). It was not possible to set the length properly due to the short threading length. Calibration of the planetary mechanism was occasionally not done during marches, leading to leeway in the gears and brakes.
- Instruments: the following instruments broke in the 29th IGTR:
- 4 amperemeters
- 1 tachometer
- 4 manometers
- 3 aerothermometers, due to shocks. The devices are not only destroyed by shocks from shell impacts, but from regular use, mostly due to scale mistakes. Amperemeters and manometers break from defects of mechanical components.
- Electric equipment:
- 2 STE-128 batteries are not enough to meet the electricity demand. Occasionally, the work of the radio was limited by a lack of energy in combat. Timely recharging of batteries when support units lag in mud is not possible. It is necessary to equip the tank with 4 batteries.
- It is possible to spill gas-oil on the driver's electrical panel when fuelling up the tank.
- The faults in electrical firing mechanisms of the gun and machinegun can be explained by torn wires in the place they are welded to the connector. It is necessary to introduce holders for wires that go to the solenoid so that the bending of the wires does not stress the connector.
- Vision in the tank: the presence, amount, and quality of observation devices for the commander and loader allow for good observation of the battlefield, according to the crews. The driver's observation devices can be splashed with mud, making them hard to use.
- Winter startup device:
- The heating of air intake is deemed an effective measure for easing the startup of the engine in the winter. These devices worked perfectly on all tanks with the exception of two cases where the fine cleaning filter pipe broke. These pipes are insufficiently robust.
- Oil antifreeze system: antifreeze is poured into tanks twice before a long-term stop. Engines turn easily after pouring in antifreeze. It was not possible to establish the time it takes for the antifreeze to evaporate completely during non-stop engine work.
- Cooling system heating: the heating system, combined with the oil antifreeze system, makes it easier to keep the engine in a warmed state and ready to start. However, due to low heat production from kerosene gas, a completely frozen engine can take 3-3.5 hours to start. With carefully regulated burners, the water temperature did not rise about 50-55 degrees. With external temperature of up to -10 degrees, and the engines being warmed up every 12 hours, the engines started after 3-4 tries.
Keeping up warm conditions requires careful observation of the burners, as the wicks burn out quickly, a burnt out wick causes soot to build up, and temperature quickly drops.
- Tools: the tools provided with the tanks are incomplete. Wrenches of certain sizes are not present. No tanks have attachments for injecting oil into the main friction clutch bearings. The provided wrench for tightening the main friction clutch does not fit. The temporary regimental toolkits should be revised."