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Object 701 Trials

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 "February 8th, 1945

  1. The Object 701 tank was designed on the initiative of the Kirov factory with participation of the Bauman Institute transmission design group and TsAKB arms designers, and produced according to GOKO decree #5583 issued on April 8th, 1944.
  2. According to order #368/01 of the Commander of Armoured and Mechanized Forces and the People's Commissariat of Tank Production, the commission led by Lieutenant General of the Tank Forces comrade Vershinin conducted proving grounds trials of the Object 701 heavy tank in June-July of 1944.
    The NIBT proving grounds held penetration trials of two variants of the hull and turret in July-August of 1944.
  3. Mobility trials of the two new prototype tanks showed that the transmission is not yet sufficiently mature. The right final drive and gearbox broke several times during trials of the tank.
    Heating of the oil in the final drives and gearbox limited the extent of the trials.
    Due to the aforementioned defects, the commision conducting the trials withheld acceptance into service. The commission recommended improving the transmission of the tank and presented a list of changes and suggestions to correct the vehicle's drawbacks that were discovered both during the mobility trials and penetration trials.
  4. The factory worked on improving the overall design of the tank as well as the transmission and armour in August-December of 1944. In December of 1944, the factory presented an improved prototype for proving grounds trials.
    A number of changes were made to the tank.
    The friction clutch margin in the gearbox was reduced from 8 to 2.5, which reduced inertial load in 5th gear.
    The modulus, offset, and number of teeth in the spur gear pair was changed.
    The factory made the following changes to the tank's armour:
    • Increased the thickness of the turret armour from 160 to 200 mm
    • Increased the thickness of the upper front hull armour from 120 to 140 mm
    • Increased the thickness of the upper side hull from 120 to 160 mm
    • Reduced the thickness of the rear side armour from 140 to 120 mm, reinforcing the dovetailed connection between these plates and the rear plate
    All of the above changes in thickness were implemented in metal at the vehicle at the factory.
    70 of the commission's 101 suggestions were implemented, the rest are in the process of being implemented.
  5. Mobility trials of the prototype conducted in December-January 1945 showed that:
    1. The average movement speed on highways and country roads are close to those of a T-34 tank in the same conditions.
      The Object 701's average speed is slightly higher than that of an IS-2 on the highway and a lot higher on country roads due to a larger power reserve and more convenient gear shifting.

      Driving conditions

      Data

      701

      IS-122

      T-34-85

      Highway

      Kilometers driven

      205

      103

      204

      Average movement speed, kph

      30.6

      29.7

      31.6

      Average total speed, kph

      30.6

      29.7

      29.7

      Country road

       

      Kilometers driven

      112

      102

      76

      Average movement speed, kph

      20.8

      16

      20.2

      Average total speed, kph

      19.4

      15.5

      20.2

      The use of a planetary transmission allows the tank to be controlled easily and gives it exceptional maneuverability.
    2. The reliability of transmission components was high. Not a single component of the transmission broke during the 1421 km long trials.
  6. The tank can be armed with one of two weapons. The production 122 mm D-25 gun can be used or the 122 mm S-34P gun.
    The ballistic qualities of the guns are the same, but the S-34P gun has a horizontal sliding breech and clears the barrel of fumes with compressed air after firing.
    Since the S-34P is not accepted into service and is not currently in production, it is reasonable to accept the D-25 gun as the tank's armament.
    In the future, the D-30 gun that clears the barrel after firing can easily be installed in the tank.
    The front hull is immune to the 75 mm and 88 mm shells with a muzzle velocity of 1000 m/s, 122 mm shells (blunt and sharp tipped) with a muzzle velocity of 800 m/s, and 152 mm AP shells with a muzzle velocity of 600 m/s.
    The limit of penetration of the sides of the hull at normal is is:
    • 1600 m for the 75 mm shell with a muzzle velocity of 1000 m/s
    • 3790 m for the 88 mm shell with a muzzle velocity of 1000 m/s
    • 4400 m for the 122 mm shell with a muzzle velocity of 800 m/s
    The limit of penetration of the sides of the hull at 30 degrees is:
    • 655 m for the 75 mm shell with a muzzle velocity of 1000 m/s
    • 540 m for the 88 mm shell with a muzzle velocity of 1000 m/s
    • 1960 m for the 122 mm shell with a muzzle velocity of 800 m/s
  7. To compare, the limit of penetration for the IS-2 tank upper front hull is:
    • 460 m for the 75 mm shell with a muzzle velocity of 1000 m/s
    • 250 m for the 88 mm shell with a muzzle velocity of 1000 m/s
    The lower front plate can be penetrated with the 75 mm shell at a range of 870 m.
    The limit of penetration for the IS-2 tank side hull is:
    • 2190 m for the 75 mm shell with a muzzle velocity of 1000 m/s
    • 6270 m for the  88 mm shell with a muzzle velocity of 1000 m/s
    The thickness of the Object 701's armour allows it to fire and destroy any German tank from a range at which it cannot be penetrated.
  8. Due to the highly mature nature of all components, maintenance of the tank will not cause any difficulties for the crew.
Conclusions:
  1. Considering that the Object 701 heavy tank:
    1. Surpasses all existing tanks in armour, matches domestic heavy tanks in armament, and matches domestic medium tanks in mobility.
    2. Can be considered ready for service based on the reliability of the transmission components in lengthy trials and implementation of changes suggested by the commission.
    3. Has room for additional improvements (armour and armament) due to a reserve in engine power and suspension load capacity that were designed to service heavier vehicles than the IS heavy tank.
    The Object 701 tank should be accepted into service with the Red Army conditional on the mitigation of all defects identified by the commission on the pilot vehicles.
  2. Send the government a request to accept the Object 701 heavy tank into service and immediately put it into production at the Kirov factory replacing the ISU-122 and ISU-122S SPGs with the intention of producing a pilot batch of 25-30 vehicles in February-March, 50 vehicles in April, and 100 vehicles in May without a decrease in the overall number of vehicles produced by the Kirov factory.
Chief of the GBTU Tank Directorate, Engineer-Colonel Blagonravov"
CAMD RF F.38 Op.11355 D.3012 L.102-105

Printed in Glavnoye Bronetankovoye Upravleniye Lyudi, Sobytiya, Fakty v dokumentakh, 1944-1945 p.370


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