Tuesday 12 August 2014


Many of the improvements found on the T-43 project carried over to the T-34-85. In 1944, factory #183 decided to carry over a few more.

T-34-85M tanks, first variant (minor modernization) and second variant (major modernization).

"1. Introduction

According to order of the People's Commissar of Tank Production and the Commander of the Armoured and Mechanized Forces of the Red Army #344S/091 issued on May 28th, 1944, the commission formed by this order tested two modernized T-34-85M tanks and one serial T-34-85 tank produced at factory #183 in May.
  • 1st variant: thickened upper front plate, without modification of fuel tanks.
  • 2nd variant: thickened upper front plate and fuel tanks moved to the rear of the tank.
Before the start of mobility trials, the tanks were tested at the factory over a range of:
  • T-34-84M #4427 (1st variant): 1204 km (according to speedometer)
  • T-34-85M #43601 (2nd variant): 1188 km (according to speedometer)
  • T-34-85 #44512 (serial production): 90 km (according to speedometer)
Note: the distances measured with T-34-85M speedometers are not accurate, as they have drive wheels with 5 bars (instead of 6 on production tanks), without modification to the speedometer. As such, the factual distance travelled is 12% less.

All trials were performed in accordance with the program approved by the Deputy People's Commissar of Tank Production and GBTU KA chief, with the exception of off-road testing, which was replaced with testing on destroyed dirt roads. Trials were performed at the Kubinka station of the Western railroad, from May 24th to June 10th, 1944.

Conclusions on the comparative trials of the two T-34-85M modernized tanks and the serial T-34-85 tank produced at factory #183

Modernizations of the T-34-85 tanks include:
  1. First variant:
    1. Increase of the upper front plate to 75 mm from 45 mm.
    2. Change of the gear ratio of the conical pair to 1.562 from 1.857.
    3. Thickening the driver's hatch to 100 mm from 75 mm and the DT machinegun ball to 90 mm from 60 mm.
    4. Decreasing the drive wheel diameter to 530 mm with five bars instead of 634 mm with six bars.
    5. Decreasing the thickness of the hull floor, roof, and over-track hull floor to 15 mm from 20 mm and the lower rear plate (connecting the floor and rear armour) from 45 mm to 15 mm.
  2. Second variant:
    1. Aside from the aforementioned changes, instead of six fuel tanks placed in the fighting and engine compartments, two fuel tanks, 190 L each, are placed behind the gearbox. The total size of the main fuel tanks remains at 540 L.
    2. Due to the changes to fuel tank layout, the rear of the tank is altered. The lower rear plate is increased in height by 400 mm, and thickness reduced from 45 to 30 mm. The slope is preserved at 45 degrees. The side fuel tanks are protected by 45 mm armour at 0 degrees and skirts from sheet metal instead of 45 mm side armour at 45 degrees on the serial tanks.
Based on the trials of the modernized and serial tanks, the commission reached the following conclusions:

1. Armour:
The armour is increased [repeat of the armour increases]while maintaining the tank's weight by reducing the thickness of the least vulnerable parts of the tank, the floor, engine compartment roof, and overtrack hull floor. This increases the tank's protection while having no negative effect on its handling and performance.

Drawbacks of the modernized T-34-85M tank's armour include:
  1. The increased thickness of the DT ball mount weakens the armour due to a larger welding seam perimeter, which causes increased pressure on the armour and decreases the margin between the UFP and DT by 30-40 mm.
  2. The second T-34-84M tank has lower protection from the rear due to the use of flat 45 mm armour instead of 45 mm armour at 45 degrees. Placing sloped armour in this location will increase the tank's weight by 150 kg.
  3. The thinner floor armour makes the tank more vulnerable to mines.
It is considered necessary to:
  1. Change the armour layout of the second T-34-85M tank, placing the rear armour plates at 45 degrees instead of 0 degrees.
  2. Maintain the thickness of the front floor at 20 degrees.
  3. Use a fixed machinegun instead of a DT in a ball mount to increase protection from the front.
2. Change of the conical pair and drive wheel

The change of the gear ratio to 1.562 from 1.857 and replacing the drive wheel with a 5 bar one has a negligible effect on the performance of the T-34-85M tanks. 

Drive wheels with 5 bars perform significantly more poorly than drive wheels with 6 bars. The smoothness of the track movement is reduced, due to the reduction in wheel size and reduction of distance between bars. Track teeth were observed hitting the bars. As a result, there was an increased degree of wear on the drive wheels and tracks. During trials, four track links from both tracks had to be removed. The alteration of the gear ratio with the aim of reducing load on the transmission is unnecessary, as:
  1. The weight of the modernized tank does not exceed the weight of the serial tank.
  2. Gearboxes on tanks produced by factory #183 have passed every trial and worked reliably since August of 1943, which indicates that the transmission is not overly loaded.
  3. A drive wheel with five bars installed due to the gear ratio change increases the load on the transmission due to the abnormal bar engagement and makes the tracks perform more poorly.
  4. A gearbox with an altered gear ratio makes a third type of gearbox installed in T-34 tanks, which would complicate delivery of spare parts.
In order to increase the performance and reliability of the T-34-85M, factory #183 should use 5-gear gearboxes and serial 6-bar drive wheels.

3. The transfer of the fuel tanks from the fighting and engine compartments to the rear (variant #2)

Moving the fuel tanks decreases the tank's chance of catching fire, increases the ammunition capacity to 60 shells and 33 MG disks (from 56 shells and 31 disks), and improves the crew work environment due to an increased size of the fighting compartment.

At the same time, moving the fuel tanks to the rear complicates installation and removal of the transmission. Replacing the brakes is not possible without removing the fuel tanks and their armoured cover. Calibration of the brakes and friction clutches, as well as access to the starter, are all made more difficult. Filling up the gearbox with oil is not possible without a special funnel or hose.

Since, during trials, the brakes and friction clutches had to be adjusted frequently, and the design of the fuel tanks makes this action difficult (the fuel tanks themselves were damaged thrice during trials), this variant cannot be recommended for production. 

The variant with altered fuel tanks can be accepted into production only if the transmission can take 500 km between calibrations, improvement in maintenance complexity, improvement in the reliability of the tanks themselves, and alteration of their design according to the proposed changes to rear armour.

4. Balance mechanism of the driver's hatch.

The new balance mechanism was in an unusable condition, having jammed. Reliable and convenient use of this mechanism is not possible.

5. Single pull-rod controls of the friction clutch and brakes.

The single pull-rod controls installed on the serial tank worked flawlessly and without issues. The agility of the tank using these controls decreases, due to a design flaw. The main disadvantage of this method is the lack of friction clutch and brake separation. When the brakes are applied, the clutch is disengaged. As a result, the driver cannot apply all his force to the brakes, and must apply some force to keeping the clutch disengaged. The brake moment generated this way is insufficient, especially when a complete stop is needed. This drawback can be resolved using the single pull-rod control mechanism from the KV tank.

  1. Considering the necessity of increasing the front armour of T-34-85 tanks, in order to supply the army with these tanks more quickly, approve the modernized tank with an increase of front armour from 45 mm to 75 mm immediately.
  2. Leave the front of the floor at 20 mm.
  3. In order to improve the robustness of the front plate, consider using the IS and T-44 type machinegun in the front, instead of a machinegun in a ball mount.
  4. Other changes to the armoured hull should correspond with the first variant (#4427).
  5. Due to the poor reliability of 5 bar drive wheels that reduce track lifetimes and lack of reason to have three incompatible gearboxes, use production gearboxes and 6-bar drive wheels.
  6. The second variant cannot be approved for production without major revisions, as the fuel tanks are unreliable and make service of the transmission and starter difficult, as well as weakening the rear armour of the hull.
  7. As it is important to remove fuel tanks from the fighting compartment, the factory should continue work on this variant, keeping in mind suggestions given by the commission.
  8. Continue work on the driver's hatch balance mechanism to provide reliable and convenient opening of the driver's hatch."

However, the follow-up ballistic tests demonstrate that the "necessity of increasing the front armour" wasn't all that necessary. The tank can now resists shells from a Panther at a distance of 720 meters and a King Tiger at 1800 meters, but the turret is still just as vulnerable as always. A suggestion is made for 90 mm of frontal armour that would "allow, at least within a narrow arc, to get within point blank range of the enemy", but the additional weight of the front plate and turret armour would definitely negatively impact the maneuverability of the T-34-85. The fateful phrase "The modernized T-34M tank has no significant advantages over the production model" puts a big fat X on the project. 

Interestingly enough, an American report on losses of 75 mm Shermans (report No.12-No.2, Operational Research Section) comes to the same conclusions. "For instance, up-armouring the front of the tank so that in the cases considered it would have given 50% protection on this face, would only have decreased penetrations by 15%. In consequence, if changes are required, it would appear wiser to use the extra weight-carrying of the 75 mm Sherman to take a better gun; ie., to make German tanks more vulnerable rather than to attempt to decrease our own vulnerability." 

1 comment:

  1. Thats the typical soviets. They will issue big efort to improve some construction, some problems will occur, they will totaly cancel all project. It seems to me, that they didnt know word called "compromise".
    I think there wasnt need to reinforce front hull armour up to 75 mm because better option would be 60 mm when the most numerous enemy anti tank gun was pak 40 and it would be enough good to deflect its shot even from the short distance. And I also have doubts that Tiger II should penetrate T34 85M front 75 mm thick armour from 1800 m because soviets did as we know penetration tests on Panthers 82 mm thick sloped armour and pak 43 had some troubles to penetrate it with its AP caped shell so it seems to me, that distances was just calculated.
    My opinion is, that improve main hull front armour to 60 mm would be very usefull and that tank would be stop something more than the bullets from machine guns.
    Because my feelings about his 47 mm armour in 1944 is this : https://www.youtube.com/watch?v=GQSOp9Njvn0

    But on the other hand, thank you good article.