Saturday 21 May 2016

IS-2 vs. IS-3

"Comparative table of tactical-technical characteristics of heavy IS-2 and IS-3 tanks

Combat weight (tons)
Length, hull (mm)
Full height (mm)
Full width (mm)
Clearance (mm)
Bore axis (mm)
Ground pressure on solid ground, kg/cm2
Armour protection, thickness and slope in mm/degrees
Upper front plate
Lower front plate
Side, vertical
Side, sloped
Turret front
Turret ring diameter
122 mm D-25 gun
DT machinegun
DShK AA machinegun
Gun ammunition
28 rounds
28 rounds
Maximum power at 2000 RPM (hp)
Normal power (hp)
Range without refueling (km)
Transmission and chassis
Friction clutch
Multi-disk, dry
8 gear
Turning mechanism
Planetary, two step with friction stopper
Floating band type
Final drives
Planetary gear
Torsion bar
Road wheels per side
Aiming and observation devices
Periscopic tank sight
Collimating sight
MK-IV observation devices



  1. This comment has been removed by the author.

  2. Seeing things that IS-3 has much thicker turret armour and bigger frontal upper hull than IS-2 frontal cast and IS-3 is overall wider, its hard to believe that there is so small weight difference. But some data about IS-2 armour thickness are interesting.

    1. I saw the IS-3 which was at Aberdeen, and it is low and compact. Hard to believe it weighed roughly the same as a Panther, with its' armor roughly twice as thick...

    2. Its the same reason why Matildas managed the same armor thickness as KVs while only having half the mass.
      In other words: If your front is half as big, you can make it double thickness for the same weight.

  3. Well Anon, that would be because the German designers were sort of dumb or at least had trouble seeing the forest for the trees. Whatever benefits there now are in putting the final drive at the opposite end from the engine for weight distribution and mechanical efficiency (and there must be some, given how common the layout is in eg. cars) is *hardly* worth the inevitable hike in hull height if you want to have a proper turret basket, and the due increase in the absolute surface area of the glacis plate ergo total volume of steel. (The accompanying size hike in the thinner side and rear plates doesn't help ofc.)

    Personally I find it harder to believe that people still keep claiming that a "medium" tank which weighed as much as the enemy's heavy without having anywhere the same levels of protection and firepower (and which suffered from chronic automotive reliability problems due to ill-placed cost-saving measures to boot) was "the best tank of the war"...

    1. Good points, Kellomies, but what about the Pershing and the IS2? The Pershing weighed about 4 tons less than the IS2 and its hull/superstructure side armor was 51 -76mm, compared to the IS2's 90 - 100mm, 76mm turret sides to 90 - 100mm. Roughly equal frontal armor. The Pershing's superstructure did not extend over the tracks. Why the nearness in weight? Would standard versus metric tons help explain things?

    2. Wide of IS-2 is 3,07 Pershing around 3,5 m. The wide of non wide-spread part is 1,61 m and wide-spread part 2,5 m. The high of non wide-spread part is twice bigger than wide-spread part (its great visible on armour schemes). Then there is another fact that hull starts extending itself just with turret.

  4. IS3 weight in the recent IS3 article is 10tons heavier: 56.5tons.

    The difference between PANTHER and IS3 is not only the armour. It´s also the mobility. The PANTHER´s 650hp (derated) engine drove the 45ton tank at 14.4 hp/ton. Original engines allowed for even 15.6hp/t.
    The IS3´s 600hp engine had to move a 56.5ton tank: 10.6hp/ton.
    The Panther consequently has a considerable edge in terms of aviable power per weight, resulting in potentially better mobility.

    1. That's a typo, the weight is 46 tons. Soviet trials say that the mobility of the Panther and IS-2 were equal.

    2. Thanks. Against IS-2, it wouldn´t be too noticably different, indeed: 14.5hp/t vs 13hp/t. Ground pressure wasn´t that different, either.

      That´s an excellent performance for a heavy tank.

      I am more amazed that they were able to cramp that much into the IS3: More than doubling the turret armour, increasing both, side and front hull armour noticably but not gaining any weight in return. IS3 is a bit shallower but both, wider and longer than IS2, and the more angled surfaces cover more area with thicker plating.

  5. Panther and IS2 likely had not the same degree of mobility on road or cross country. If soviet trials indeed state so than either the test conditions or the state of the Panther appear to be suspect.
    IS2´s hp/t was 11.2 vs Panthers 14.5 hp/t, not a minor difference. The Panther obtained a top speed in order of 10 to 15km/h faster on the road and was noticably faster off road as well. Unlike the IS, the Panther had neutral steering, and superior floatation over undulating ground.
    Turning was easier on the Panther and required significantly less effort.

    The IS´s engine had a peaked out torque at lower rpm than the Panther´s and this may constitute to the impression that it was competetively agile if measured from the static.

    1. THe HP ratio is more like 13.x v 14.x, which is not such a huge difference. The Panther is faster because it follows a long history of German tanks having very "optimistic" gear ratios - you might remember Panzer IIIs with the 10-speed gearbox can work up to 67km/h .... with a 300HP engine before they realized in later versions that a 6-speed gearbox that tops out at 42km/h is more realistic. I might also point out that the high gear turn radius of the Panther is well-known for its excessive largeness, which was not likely by choice - no one thinks a 81m turn radius is a good idea (it was probably a forced call based on what the tank can stand) and further limits the usability of that high speed. The simpler, one-radius "geared steering" may have produced a better overall result.

  6. Shermans needed and area about "half a field" to turn 180 -at any speed-, which makes the PANTHER´s turning gear substantially more advanced. The ability to steer at different speeds -including high speed- is a practical and useful instrument for a skilled driver. No sane driver would even attempt to turn 180 at, say 40km/h at low turn radius for reasons of stability. The PANTHER turned easily under more variable conditions, the same cannot be said from IS and T34.
    The whole running gear and suspension was more thought out, and gave the Panther a cross country mobility advantage, in turning, floatation, stability and speed.

    1. Numerically, the Sherman's turn radius is about 10m. Panther's turn radius is less than that only with the first gear (or pivot-steering at neutral). At the 2nd gear it is already 11m, which allows for 8km/h (if the motor is not derated), so Panther's radius is only smaller if it is crawling. Compared to the system on the Sherman, T-34 or IS, the Panther's system is certainly more complicated and it certainly requires by far the least force to steer (it has hydraulically boosted power steering), but even compared to other contemporary double/triple differential systems, its radius at top speed is too large. At top gear (thus speed), a Merritt-Brown system's radius is still only 130 feet (about 40m or half that of Panther).

      So it seems clear that the steering system, though "advanced", does not provide as much flexibility.

  7. Your description of PANTHER steering is incorrect. Pivot turns (which the Sherman could not do) is to be done at the neutral gear (no gear selection) not in first gear. The turn radius in first gear is 5m and allows the tank to turn almost within it´s own length, 2nd gear is 11m, 3rd gear led to 16m, fourth gear to 30m, 5th gear 43m and 6th gear to 81m. 6th gear was rarely used off road due to the high speed 45 to 56km/h entailing it. Many tanks (CHURCHILL, CENTURION) couldn´t even reach that speed, so lamenting about wide turn radii at such high speed seems pointless to me.The 2nd, 3rd and 4th gear were instead used on road and off-road, but the above mentioned geared radii could be augmented by decremental use of auxillery brakes to tighten up the turns, which in practice were employed by the driver at various conditions and preferably so.
    The system was additive, continous, regenerative, stable, provided light controlls and offered significantly more flexibility (including neutral pivot) than that of contemporary russian or american tanks. The british Meritt-Brown steering system was better than the PANTHERs -but not by much. It was only used in Churchill, Cromwell and Comet tanks during ww2, which as a platform fall behind the PANTHER. The Churchill does not compete for mobility at all, the CROMWELL and COMET do in terms of mobility but had a combat debut one year later and didn´t compete with the PANTHER in terms of firepower and protection (CROMWELL) and protection (COMET), respectively.

    1. Soviet trials showed that in practice, neutral steering didn't work as advertised and the tank would just turn on whichever track offered least resistance, much like a T-34 would with one track locked.

    2. It's the "(or pivot-steering at neutral)" bit, and you missed the 6th gear's ~60m. 81m is 7th. In the 6th gear, Panther made ~42km/h when then engine is 3000RPM so we can infer at 2500RPM (post-derating) the limit is ~35km/h which is about the same as Centurion, and further Cromwell and Comet both go faster than Panther's derated speed yet they use the same gear (5th) as the Centurion.

      You are also right Panther allows for skid-steering. However, for one thing, so does the IS series, the T-34 and even the Sherman (though the last is not really designed to facilitate that, so you'll need an enormous amount of force). The problem is that real Panthers can only do it up to 13-16km/h before the engine starts crapping out. In other words, just as the radii get large and you are starting to miss the tight turns ... it stops working.

      Panther's system is not quite additive - when you slow down one track, the other track stays at the same speed. It is an "advanced" system (though the ultimate in advancement in WWII steering systems will actually be the French with their B1bis offering infinite selectable turns). However, it is not necessarily practical and flexible in one of the most important ways (choice of radii regardless of speed), and the end result is that tests show when the path is curving, Panther actually winds up slower than Sherman and the main fault is attributed to the overly large turn radii.

      As for the Meritt-Brown system, it does have a practicality disadvantage in that it can't skid steer (the control configuration deprives the driver of even the theoretical opportunity to access individual main brakes). Thinking positively the designers may thought such opportunities would be few and the control ease of simultaneously engaging both brakes outweighs it, but it might have been nice to retain the option.

    3. Only in one specific trial with a captured early Ausf. D model were problems in neutral pivot encountered. Another, later soviet trial makes mention that the PANTHER in neutral gear turned easily with only 5kg lever force while the COMET turned only after three attempts with 20kg lever force.
      Still, in the 1st gear the tank turns easily and within 5m without applying skid brakes, which is tighter than allied tanks. Any steering which allows for different turning radii is preferable to a system which only allows for one turning radius as in soviet tanks / Sherman. 16m at 3rd gear is not a big turning radius. The PANTHER uses much less engine power during turns due to the power regenerative effect.
      The actual WaPrüf data for PANTHER Ausf. D with 3000rpm gives 55km/h at 3000rpm in top gear, dropping to 48 Km/h at 2500rpm (derated already) and 46km/h for heavier Ausf. A/-G. with Schürzen(2500rpm), both on hard surface, representing their vehicles maximum road speed.
      To put it in perspective: The CENTURION pilot prototype tank in april 1945 recorded a maximum road speed attained in trials of only 38km/h in top gear (23.7mph). The post war CENTURION Mk 2 and Mk 3 had a maximum theoretical top speed on the road(!) of only 34.5km/h =21.4mp/h due to gouverned engine. The mean speeds were lower: In 100mls trials the mean for the Cent Mk 2 was 32km/h (19.9mph) on the road and off road the practical speed was only 20km/h (12.6mph).
      Off road, PANTHER did comfortably ride at 24km/h though Wa Prüf data include datapoints up to 42km/h over undulating ground in tests, which is significantly higher than any other tank tested and a testimony to the smooth ride offered by the suspension The CENTURION or IS2 couldn´t even go that fast on an even road. This figure does not mean that PANTHERs went that fast in combat off road, it was a test to explore the limits of the suspension system.
      The ability to exert high speed off road while keeping platform stability was a hallmark of the PANTHERs suspension and steering system, in this point PANTHER was among the most capable ww2 medium tanks.
      Practical speed of IS2 was 8-12Km/h off road, which is considerably lower than PANTHER. And many of the 1944 made IS2 kept receiving derated 520hp V11 engines instead of the 580hp V11 ones planned for.

    4. There is no argument in the fact that Panther's hydraulic boost is more powerful than Comet's.

      16m is not so big, BUT the tank can only move at 13.3km/h in that regime, IF it weighs only 44.8 tons AND its engine runs at 3000RPM. Beyond that and its the 4th gear and the radius nearly doubles (it's also about when the auxiliary steering system stops working).

      The statistic is interesting and confirms the impression that Panther's speed advantage (which no one denies) is derived by using the equivalent of an overdrive for its top gear ratio - it's set so low that even a relatively small increase (addition of 700kg mass) in rolling resistance immediately slows the vehicle. You can extrapolate that a Ausf G with a 3000RPM engine will do around 52-53km/h.

      Centurion and IS went for more conservative ones.

      I'll be a bit cautious of comparing off road speeds from different countries because so much depends on the test condition (for a road, at least there is some assurance it is flat and paved). Indeed, one must wonder how relatively flat the "undulating ground" must be for Panther to be able to reach 42km/h on it, simply as a matter of available power.

  8. The description that the skid steering cease to work in 4th gear is a mistaken one. Instructions to driver suggets using skid steering to tighten turns temporarely. Altough it will tighten the turn somewhat, it will also bleed off speed very fast. Tighter turns are thus not sustainable at this or higher gears. The engine is stalling -if the rpm drops below a certain range -before which point the driver was advised to switch to 3rd gear, anyways. Tank steering is a dynamic and not a static process, and any meaningful analysis should take these factors into account. A contemporary T34/85 would need to resort to entire clutch braking and bleeding off speed almost completely off road while making a 3 point turn at any speed.
    PANTHERs were faster off road than other tanks, including early model CENTURION and COMET tanks. PANTHERs were capable to negotiate significantly more difficult terrain than Shermans.
    The 7th gear might be a luxury to offer high road speed, however, it was a luxury neither the IS nor the CENTURION could compete with.
    The maximum safe off road speed in undulating ground for the series PANTHER was determined as 44km/h on the 1km undulating test track -though the engine power required to obtain this required the surface not to be soft. The suspension allowed high speeds off road without exceeding it´s limits.
    The T-34 based Su-85 in similar tests was exceeding it´s suspension limit already at 26 km/h (on hard ground), same speed for TIGER Ausf. E, Pz-IV series was limited to even slower 22km/h, FERDINAND to 21km/h. Late model Sherman were also reasonable and allowed for 37km/h on hard, undulating ground before meeting the suspension limits.
    In addition, none of these tanks could compete with the PANTHER in aspects of platform stability during the move.
    Mobility advantages for the PANTHER are real.