The 120 mm T53

T34

You have probably heard about the American experimental heavy tank T34 somewhere, maybe from World of Tanks, War Thunder or Wikipedia. It’s described as having an excellent penetration at about 247 mm from 100 m, which is a feat compared to the German 8.8 cm KwK 43 gun armed on the Tiger II. But did you know that it could do more than that?

A bit of Background

The T34 was a WWII prototype heavy tank developed in 1945 in response to the German armored threats such as the Tiger II and Jagdtiger. The T29 was considered satisfactory enough in term of performance with its 105 mm T5E1, but lacked serious firepower in contrast to the 12.8 cm cannon. The T30 was only armed with a 155 mm as a bunker buster, with sub-par anti-tank performance across the board. As such, a project was initiated to rearm the T29/T30 with a modified 120 mm M1 AA gun, the 120 mm T53 L/65. Firing a 23 kg heavy projectile at 960 m/s, the gun was able to closely match the performance of said German gun. Unfortunately for the Americans, World War II was already over by the time the T34 was assembled. Post-War development led to the T34’s engine being upgraded from using the Ford GAC to Continental AV1790. Extensive trials of the T34 as a “technology demonstrator” led to the M103 Heavy Gun Tank.

Development

The earliest known record of the requirement to develop the T34 heavy tank was from the first of February, 1945. The Army expressed concern about using the 155 mm gun with heavyweight 100 lb projectiles on the T30 (M112B1), mainly because of the effectiveness of it against enemy tank armor, with the rate of fire calculated in. It was expected to be very ineffective (the M112B1 only penetrates 170 mm of armor from point blank, while the rate of fire from the gun is only 3 RPM). Seeing the potential problem that would likely cause an unnecessary issue in the future, the Ordnance Department went to study for possible application of the 120 mm M1 anti-aircraft gun for the heavy tank.

Screenshot_6

In the sixth of June, 1945, a report arrived about the anti-air equipment, explaining the importance of the AA gun to be able to return fire against enemy armor, in this case, the 120 mm M1 AA gun. A project was initiated to develop an APCBC round, capable of penetrating heavy armor, face hardened or homogeneous structure at high obliquity, designated as 120 mm T14. This shell would also be used later on the 120 mm T53 gun mounted on the T34 heavy tank.

SR34/148

As of eighteenth of June. From the next report, an outline of the 120 mm T53 development was given:

A 120 mm gun was developed for installation for the T29 and T30 heavy tanks. The weapon will have the ballistic characteristics of the 120 mm M1 AA gun, giving a muzzle velocity of 3100 ft/s to a 50 lb projectile. A muzzle brake is being provided. Design studies have been completed and work on detailed drawing is in hand.

SR35/125

Proposed ammunition for this weapon includes a 50 lb APCBC shot (10% piercing cap) (SR 34/148); an HVAP round and an all purpose HE shell which, with the M78 fuze will be used for the attack on concrete and with fuze PD M48 or T & SQ M54 for normal fragmentation. The 120 mm HE AA shell M73 will not be suitable for use with this weapon. As optimum functioning against concrete with the M78 fuze is obtained at around 2200 ft/s, the decrease in capacity which might have resulted from the increased nose section required for attack of concrete, is being compensated for by a reduction in the amount of metal at the base.

It is understood that the design of this weapon follows that of the 90 mm T54 (para 122). A contract has been placed for 2500 rounds of 120 mm APC T14, of which the first two experimental lots, one assembled with a soft, and the other with hard steel cap have been delivered.

The ammunition development notes for the 120 mm shell came a month later, in July. The ammunition load consisting of T14 APC, T15 HE, T16, and T17 HVAP, accordingly.

SR36/164

Screenshot_9

Another detail on the 120 mm T15 HE shell came later, in August, mentioning the purpose of this shell against concrete.

SR37/152
120 mm M356 HE of the M103 heavy tank had a prototype T15E3, an improvement of this HE shell of the T34 heavy tank.

Utilization of these shells was still ongoing until 1949, where the specification & performance of these shells were given in a comparative data for 120 mm heavy tanks from Detroit Arsenal Automotive Development Conference in 1949, at the point where an APDS was issued along the way to test the feasibility of using sabot rounds for the 120 mm gun. This marked the beginning of the M103 heavy tank and the end of the T34 as a test bed for the former tank.

Detroit Arsenal

Shell Specification

T14 / T14E1 / T14E3 APCBC

Solid armor-piercing round initially developed for the 120 mm AA gun unit, later available for the T34 heavy tank. It had 2.26 kg (5 lb) heavy penetrating cap and capable of penetrating 152.4 mm (6″) armor at 45° with a ballistic limit at 677 m/s (2878 ft/s).

There is a complete ballistic limit of the T14 series against rolled homogeneous armor from An Analytical Study of Data on Armor Penetration by Tank-Fired, Kinetic Energy Projectiles. Take an example from the T14E3 (since it has more test results):

The ballistic limit given is 756 m/s against 203 mm at 0° from vertical. The muzzle velocity of the shell is 960 m/s, which will result to 286 mm from point blank range.

Screenshot_1

Specification:
Weight: 22.67 kg
Muzzle velocity: 960.12 m/s

T15 HE

An all purpose HE shell, developed only for 120 mm tank version because the unsuitable M73 HE shell. 3 kind of fuzes were available: M78 fuze for anti-concrete, M51 for direct impact, and M54 for normal fragmentation. As optimum functioning against concrete with the M78 fuze is obtained at around 2200 ft/s, the decrease in capacity which might have resulted from the increased nose section required for attack of concrete, is being compensated for by a reduction in the amount of metal at the base.

It’s unknown what exactly is the explosive composition of the 120 mm T15 HE, but assuming the T15E3 was developed from it, the explosive should be similar.

Specification:
Weight: 22.67 kg
Muzzle velocity: 762 m/s
Explosive type: Composition B
Explosive weight: 3.55 kg
Fuze: C.P. M78 (concrete-piercing), P.D. M48A2 / M51A1 (point-detonating), T. & S.Q. M54 (time and super quick)

T16 WP

Smoke shell, used to provide smoke screen with 15.6 lb (7.07 kg) of white phosphorous. Unfortunately there is no known information of its smoke filler. But if we take an example of the 155 mm M110 WP weight-to-filler ratio (6.31), it gets an estimated weight at 3.59 kg.

Specification:
Weight: 22.67 kg
Muzzle velocity: 762 m/s
Smoke type: WP
Smoke weight: (?) – Estimated to be 3.59 kg
Fuze: P.D. M51A3

T17 HVAP

High velocity armor piercing / composite rigid projectile, taking similar design to the 105 mm T29E3 of the T5E1 gun. Situation Report No. 37 indicated the complete weight between 13.6 – 14.5 kg (4.5 kg tungsten carbide core) with muzzle velocity between 1188 – 1219 m/s. But there is a conflicting sources between each sources, 3 in total.

1. One is from Situation Report, which is using this specification.

1st Specification:
Weight: 14.51 kg
Muzzle velocity: 1219.2 m/s
Core diameter: (?)
Core mass: 4.5 kg
Core type: Tungsten carbide

2. Another one is from Detroit Arsenal Automotive Development Conference, indicated an increase to its weight at 16.32 kg (7.25 kg tungsten carbide core) with drastic muzzle velocity drop at 1082 m/s.

2nd Specification:
Weight: 16.32 kg
Muzzle velocity: 1082.04 m/s
Core diameter: (?)
Core mass: 7.2 kg
Core type: Tungsten carbide

T17E1 Mod. 0 HVAP

3. The last one is from Table of Form Factors of Projectiles, 1958. This shell retained the similar specification from the Situation Report, but went with different designation.

3rd Specification:
Weight: 12.7 kg
Muzzle velocity: 1264.92 m/s
Core diameter: (?)
Core mass: (?) – Probably same as the T17, 4.5 kg
Core type: Tungsten carbide

As far as the performance goes, all 3 different rounds will have different penetration, naturally. But assuming we use the T17E1 instead, extrapolating the number from 90 mm M304, the penetration could be achieved at 456 mm from point blank.

There is also this little specification sheet from the T34 heavy tank, with unknown HVAP designation penetrating 393 mm against vertical armor from 914 m away. It could be anything from the first version to third version.

uyoZEnC

Conflicting Sources

There is a conflicting source between Situation Report and Hunnicutt: Firepower in term of loadout, which also contributes as the 4th specification of the “HVAP” projectile.

Screenshot_1

The first one is the “Test Shot T20E3 APBC” round. As far as I look into all possible sources pertaining to 120 mm gun tank development, there is no such known designation as “T20E3” for 120 mm projectiles ever mentioned. It’s only listed from Hunnicutt’s book.

The second one is the HVAP with an unknown designation. There is next to none specification of it from the datasheet, not even the projectile weight or the velocity. Only the penetration figure is given, and so far the penetration appears to be overperforming at 60° angle (112 mm from 914 m).

As a side note. Something to look from games perspective are World of Tanks and War Thunder. WoT seems to be using completely fictional name again for projectiles they couldn’t find on common historical books. Each are T42 AP, T62 APCR, and T67 HE, and could be renamed to T14, T17, and T15 respectively. The penetration buff can also be applied, but that would cross the border as OP premium tank, since no Tier 8 heavies pack more than 280 mm penetration (the T34 itself already has the highest penetration out of all heavy tanks at 248 mm). For WT, just about everything is wrong with the gun. First of all, the muzzle velocity is slightly off for the T14E3 AP (944 m/s instead of 960 m/s). Its shell type is wrong too (AP instead of APCBC). But the hardest one is drastic penetration difference, due to the T14E3 AP was just a renamed T20E3 back in the 1.75 Dev Server (247 mm instead of 286 mm). So far, the T17E1 one takes the specification from Table of Form Factors of Projectiles, while having right specification, the penetration is hit extremely hard (barely 324 mm instead of 424 mm from PB). The HE shell is the M73, which as previously said, is unsuitable for use with the 120 mm T53. It should have been replaced with the T15 HE instead. Numerous bug reports have been sent, and the inaccuracies should be fixed as soon as possible.

Guess that’s all for this weekend.

Sources:

  • New Tanks and Gun Motor Carriages, 1945
  • Development History of the Heavy Tanks, T29 & T30, 1945
  • RAC – AFV Technical Situation Report, 1944 – 1945
  • AD0802080 – Table of Form Factors of Projectiles, 1951
  • AD301343 – An Analytical Study of Data on Armor Penetration by Tank-Fired, Kinetic Energy Projectiles, 1958
  • R.P. Hunnicutt: Firepower – A History of the American Heavy Tank, 1988
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14 thoughts on “The 120 mm T53

  1. Was it you who wrote the excellent piece on the 155 mm projectiles?I believe you left out one,the HEAT round developed later for the version fitted to the T58.

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  2. «For WT, just about everything is wrong with the gun»
    no surprise there
    «Numerous bug reports have been sent, and the inaccuracies should be fixed as soon as possible»
    it has been almost a year since then and there’s no sign of it being changed soon

    btw, about the APDS you mentioned, was it ever supplied to the M103?
    I remember a WT dev mentioning it was highly possible that a T32E1 and M103E2 would be added and I believe he mentioned the M103E2 would get stabilization and APDS, don’t know if he was correct

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  3. “Only the penetration figure is given, and so far the penetration appears to be overperforming at 60° angle (112 mm from 914 m)” considering that 90mm T44 breaks 102mm 60 degree, there is chance for larger 120mm one APCR

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    1. But there is only limited amount of sources available about the 120 mm weapon development to find.

      APCR designs are also getting inconsistent every time.

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      1. i know, but comparing to performance of other APCR it seems to low
        90mm M304 penetrates 76mm at ~1400yards (3285f/s) when fired from T15/T54.
        and 120mm less than that? ( according to table)

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  4. Great article, keep them coming, I wonder what the armor penetration of the concrete shell was and if it is viable for in game

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