The Soviet Bear: The IS-2 and the D-25T

The Soviet Bear:
The IS-2 and the D-25T





Contents

Shared components (of both models 1943/44):

1. Gun D-25 series

1.1 Development

1.2 Gun

1.3 Ammunition 
- 1.3.1 Armour piercing
- 1.3.2 High explosive

Gun D-25 series

1.1 Development

Gun D-25T is a Soviet anti-tank gun. It was developed from the A19/22 or the M1931/37 gun of the same calibre (122 mm). D-25T. T stands for “Tank (model)”.

The D-25 was the initial variant, which was itself just a plain redesign of the A19. The D-25 created the IS-122 prototype. It would be somewhat of a stopgap, for now, at least. 

The redesign came, beginning August 1943 after it was proposed by Zhozef Yakovlevich Kotin (Joseph Kotin) after the Battle of Kursk, citing excellent performance of the 122 mm guns against German armour. The Design Bureau of OAO Plant No. 9 based in Yekaterinburg would be then ordered to urgently develop a tank model of the A19.

In September 1943, the infamous artillery designer Fyodor Petrov would write a letter to Joseph Kotin. After agreeing on technicalities, core qualities of the design and gaining permission from Iosif Stalin to mount the prospected new gun on the IS-2, they continued development. 

In November 1943, the D-25T was developed. The development, headed by Fyodor Petrov, would be completed in Plant No. 9 and finalised. 

After being finalised, the D-25T would be immediately placed into production at Plant No. 9. However, due to problems in trying to master the production and gun itself, the A-19 again came into consideration for mounting on the IS-2. Thankfully, the doubts would be quickly cleared as production went up and the D-25T would proceed with its production and life accordingly.

Sometime in development, the tank was fitted with three kinds of muzzle brakes (Photo courtesy of Tank Archives);

T-shaped

"German" style

New and original design

The T-shaped muzzle brake was very unreliable and exploded once during testing, almost killing the attending Marshal of the Soviet Union Konstantin Rokossovskiy.

A model of the D-25T for tank destroyers and self-propelled guns was also developed, called the D-25S. It bears almost no serious difference to the D-25T.

1.2 Gun

The D-25T is significantly lighter than the A-19. The D-25T also bears a muzzle brake to mitigate recoil, which was an issue in the D-2/D-5 guns. There were also more compact recoil mitigation devices (presumably springs) and the firing controls were moved to one side of the cannon to reflect its usage inside a cramped fighting condition. The D-25T also bears an electric trigger.
In early 1944, the D-25T received a semi-automatic wedge gate. Production would continue with this feature.
The calibre of the D-25T is 122 mm. Precisely, 121.92 mm. 

In the turret of the IS-2 Obr. 1943 and 1944, the elevation rate of the D-25T was +20° degrees and -3° degrees (in ideal conditions), however usually, the depression was down to just -2° degrees.

The average reload rate of the IS-2 was 2 - 4 rounds per minute, or 30 - 15 seconds. However, a realistic expectation would be 30 - 45 seconds for one shot, as the IS-2 turret was extremely cramped (for such a gun, and partly due to such a gun) and had 2 piece ammunition, thus the long reload times.

The barrel length is 5,852 mm, with a maximum range of 19,800 metres (of course, depending on shell). The gun weighed 2,400 kg, which was a far cry from the A-19's 7,119 kgs. It had a maximum rollback length of 570 to assist with mounting.
The D-25T had a maximum bore pressure of 2,750 kgf/cm² (270 MPa) and a maximum muzzle energy of 8.09 MJ, which was quite large for such a gun, even exceeding some early APFSDS projectiles of the 2A45/46.

Often, the IS-2 only had 27 - 28 rounds of ammunition.

1.3 Ammunition

The D-25T has a very diverse set of ammunition choices, ranging from HE to AP, and later HEAT and some sub-calibre rounds that were developed in the Cold War.

1.3.1 Armour piercing rounds

The D-25T’s main armour piercing rounds would be the BR-471 (sometimes referred to as the BR-471A) and the BR-471B.

BR-471B:

Projectile 53-VBR-471B and 3VBR2 uses an armour piercing tracer and a blunt head with a ballistic cap 53-VBR-471B. APHEBC shot. The shot began use and production in 1944, however it never saw proper frontline use until spring of 1945. The development of a blunt-nosed BR-471B was inspired by an event in which the BR-471 penetrated a Panther's UFP (80 - 84/85 mm) at a range of 1,500 metres. The BR-471's sharp nose was more prone to shell shattering and cracking, so a blunt nose with a ballistic cap was used instead.

(There will be a separate post on the ammunition of the D-25T. This is supposed to be done quicker and will be much more summarised.)

Composition of the shot:

53-VBR-471B (Whole shot)
- projectile 53-BR-471B with fuse MD-8 or DBR and tracer No. 7
- full variable powder charge 54-Zh-471, 54-ZhD-471, 54-ZhK-471, 54-ZhN-471 or 54-ZHN-471K

3VBR2 (Shot)
- projectile 53-BR-471B with fuse MD-8 or DBR and tracer No. 7
- a charge in a cartridge case with a burning case 4Zh2

Specifications:

Weight:
Shot is 40 kg
Shot 3VBR2 is 35.1 kg
Projectile is 25 kg
Internal explosives AI-X-2 is 156 grams (0.156 kg)
Propellent charge Zh-471 series is 10.8 kg

Dimensions:
121.92 x 419 mm (projectile)

Ballistics:
Muzzle velocity: 781 - 800 m/s (sources vary, 800 m/s is most commonly cited)

Maximum range:
4,000 metres

Direct firing range:

Target height	Range
2 metres	970 metres
2.7 metres	1120 metres
3 metres	1180 metres

Armour penetration:

Degrees	Range	Penetration
90	100 metres	165 mm
90	300 metres	160 mm
90	500 metres	155 mm
90	1,000 metres	145 mm
90	1,500 metres	135 mm
90	2,000 metres	125 mm
90	2,500 metres	115 mm
90	3,000 metres	105 mm

Degrees	Range	Penetration
30	100 metres	135 mm
30	300 metres	131 mm
30	500 metres	125 mm
30	1,000 metres	120 mm
30	1,500 metres	110 mm
30	2,000 metres	100 mm
30	2,500 metres	90 mm
30	3,000 metres	85 mm

US diagram of 53-VBR-471B shell

Soviet technical drawing of the BR-471B (53-VBR-471B)

Rest of BR-471 variants:

APHE shot BR-471 (53-VBR-471) is almost no different to the BR-471B with the exception that it only ever used the MD-8 fuse, and was without a ballistic cap, using a sharper nose.

US technical drawing of a 53-VBR-471.

APCBC/APHECBC shot BR-471D (53-VBR-471D) is a post-war design, which was most notably used in the IS-3 and IS-3M/MK (but that's for another time) and many big IS prototypes. It possesses improved penetration over the previous rounds.

Ballistic qualities chart.

According to the chart above, we can conclude the BR-471D's penetrative capabilities as such:

Degrees	Range	Penetration
90	500 metres	185 mm
90	1,000 metres	170 mm
90	1,500 metres	155 mm
90	2,000 metres	145 mm
90	2,500 metres	135 mm
90	3,000 metres	125 mm

According to the chart, the BR-471D retains great penetration of around 30 - 35 mm above the BR-471B at the range of 500 metres and 1,000 metres respectively. However, according to the chart, the BR-471B also retains a significantly lower value of penetration than its original, thus the 1,500 metres to 3,000 metres bracket penetration for the BR-471D is 20 mm higher than the BR-471B.

1.3.2 High explosive rounds

The D-25T, itself being derived from a howitzer is no stranger to high explosive rounds. The main rounds being used here would be the OF-471 and OF-471N.

OF-471:

The (53-VOF-471) OF-471 was available for use in the D-25 series of guns ever since it began development, as it was already in use for the A-19 field gun.

Composition of the shot:

53-VOF-471 (whole shot)
- Solid-body projectile 53-OF-471 
- full variable powder charge 54-Zh-471, 54-ZhD-471, 54-ZhK-471, 54-ZhN-471 or 54-ZHN-471K

Projectile 53-OF-471
- Projectile 53-OF-471 with RGM or RGM-6 fuse

Specifications:

Weight:

Shot is 40 kg

Projectile is 25 kg

Internal explosives is 3.6 kg

Propellent charge Zh-471 series is 15 kg

Ballistics:

Muzzle velocity: 792 - 800 m/s (sources vary, 800 m/s is most commonly cited)

Maximum range:

19,800 metres

Anti-armour performance:
In early November of 1944, a captured Tiger II (Tiger Ausf. B) of the Wehrmacht was tested in Kubinka.

The OF-471 successfully destroyed the Tiger II's hull welds and disabled the transmission. It is quoted by some as being "1.39 times more effective than (the KwK43's) the German 88 mm high explosive shot."

OF-471N:

The (53-VOF-471N) OF-471N is a model/derivative of the OF-471 where it has a screw-on fuse head. It is different also in the fact that it has 200 grams more explosive than the OF-471.

Composition of the shot:

53-VOF-471N (whole shot) derivative 1
- Screw-on head projectile 53-OF-471N/53-OF-471NZh
- full variable powder charge 54-Zh-471, 54-ZhD-471, 54-ZhK-471, 54-ZhN-471 or 54-ZHN-471K

Projectile 53-OF-471
- Projectile 53-OF-471 with RGM or RGM-6 fuse

Specifications:

Weight:

Shot is 40 kg

Projectile is 25 kg

Internal explosives is 3.8 kg

Propellent charge Zh-471 series is 15 kg

Ballistics:

Muzzle velocity: 781 - 800 m/s (sources vary, 800 m/s is most commonly cited)

Maximum range:

19,800 metres

Anti-armour performance:
The anti-armour performance is nearly identical to the OF-471's, however it could have higher anti-personnel and anti-structure properties owing to an extra 200 grams of explosive (which is quite a lot).

Comparison between A (OF-471, on the left) and B/б (OF-471N).
See how the OF-471N has a shorter cap, with a screw-on cap.

Sources:

IS-2 gun,
Part 1.1: 

И. Желтов, И. Павлов, М. Павлов, А. Сергеев. Танки ИС // Танкомастер (спецвыпуск). — 2004. (part one) (Web version)

И. Желтов, И. Павлов, М. Павлов, А. Сергеев. Танки ИС в боях // Танкомастер (спецвыпуск). — 2002. (part two) (Web version)

И. Желтов, И. Павлов, М. Павлов, А. Сергеев. Танки ИС. Боевое применение // Танкомастер (спецвыпуск). (part three) (Web version)

Свирин М. Н. Стальной кулак Сталина. История советского танка 1943—1945.

Part 1.2:
BTVT

М. Свирин. Артиллерийское вооружение советских танков 1940—1945. // Армада-вертикаль, № 4, С. 31—32. (page 31 - 32)

Part 1.3:

BR-471B
Photo courtesy of bulletpicker

М. В. Павлов, И. В. Павлов. Отечественные бронированные машины 1945—1965 гг // Техника и вооружение: вчера, сегодня, завтра. — М.: Техинформ, 2008. — № 9. — С. 55. (page 55)

Широкорад А. Б. Энциклопедия отечественной артиллерии / Под общ. ред. А. Е. Тараса. — Мн.: Харвест, 2000. — 1156 с. — (Библиотека военной истории). — ISBN 985-433-703-0.