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Soviet Union's IS-85¹, IS-1¹, JS-1⁷ heavy tank

IS-1 heavy tank with 85 mm:

IS-1 heavy tank:

Design

IS stood for Iosef Vissarionovich Stalin.²

The need to increase the firepower of the KV series was seen by the end of 1942 with the Germans introducing Tiger tanks a new tank was needed to combat it.² The IS-85 was intended to be a 4-man tank, with an 85 mm gun, not weigh more than a KV-1, and that had thick enough armor to defeat the German 50 mm anti-tank gun.⁷

The IS-85 was designed by a design bureau led by Lieutenant-Colonel Kotin.¹ He split the bureau into two and each team had different specifications to design for.¹ One of the teams was told to improve the KV series as a stopgap for a new heavy tank.¹ This design was to become the KV-85.¹ The other team was to design the new heavy tank, the IS-85.¹ The team was headed by, released from a labor camp, N. V. Tseits.¹ The design was initially called the KV-13 and had a redesigned hull and chassis from the KV series.¹

Based on the KV series it had a new hull, improvements in the suspension, transmission, and power train.¹ The turret was cast and the hull had cast and rolled parts welded together.^1,2

Main Armament

The IS-85's design first started out with same 85 mm gun as the T-34/85 and a few were produced in late 1943. The cast turret (which was used in the KV-85) was designed by General A. A. Petrov.² A heavier gun was needed as the T-34/85 was being produced and having a heavy tank with the same armament as a medium was thought to be inefficient. The 100 mm designed by V. Grabin was tried with great success and known as the IS-100.² The 122 mm was tried but it was only a little more effective, however the 100 mm was in short supply. The superstructure extended out over the tracks and this allowed for a bigger turret.⁵

There was no MG in the hull which allowed for a better ballistic shape.⁵

Prototype

A design bureau was headed by N. F. Shashmurin at Tankograd in the Urals that developed the IS series.² By the end of 1943 prototypes were available.²

Only a short test was done and the State Defense Committee approved the tanks for use in the Red Army in October 1943.²

The KV-13 prototype was tested at Chelyabinsk's Experimental Test Factory in May 1942.¹ It was found to have problems with the transmission and would often throw a track.¹

Production

After a few models were produced, production was switched to the IS-2. The models that were left were converted to IS-2 standards.

In 1943 the IS-85 was redesignated the IS-1.¹

• IS-1:
  • 1943: 100, 67⁶
  • 1944: 40⁶

Variants

• KV-9²: Prototype.² 122 mm howitzer.²
• KV-13^1,2: Prototype.^1,2
• IS-1 (85)⁸, IS-1:
• IS-1 (122)⁸, IS-1B:

Usage

Some saw action in the Ukraine in early 1944.

	IS-1, IS-1 (85)8	IS-1 19432, IS-1A5	IS-1B5, IS-1 (122)8
Crew	43,4,5,6,7,8	42,5	45,8
Physical Characteristics
Weight	97,000 lb, 44 tons4,6,8, 45.3 tons3,7 46,000 kg3,7	44 tons2	44.5 tons8
Length w/gun	27.3'4,8, 27' 3"3,7, 29' 4" 8.32 m3,7, 8.56 m6	8.56 m2	31' 6"8
Length w/o gun		6.77 m2
Height	8.9'4,8, 9' 6"3,7 2.735 m6, 2.9 m3,7	2.73 m2	8.9'8
Width	10' 3"4,8, 10' 8"3,7, 11' 3.07 m6, 3.25 m3,7	3.07 m2	10' 3"8
Width over tracks
Ground clearance	0.47 m6	0.46 m2
Ground contact length	14.3'8 4.3 m6		14.3'8
Ground pressure	0.78 kp/cm2 6	0.78 kp/cm2 2
Turret ring diameter
Armament
Main	85 mm3,4 85 mm M19438 100 mm7	85 mm M1943 D-5 T2 85 mm or 100 mm5	122 mm5 122 mm M19438
Secondary
MG	2: 7.62 mm DT MG3 4: MG4 2: 7.62 mm MG7 3: 7.62 mm MG8		3: 7.62 mm MG8
MG - coaxial		1: 7.62 DT MG mm2
MG - rear		1: 7.62 DT MG mm2
MG - hull		1: 7.62 DT MG mm2
MG - antiaircraft	1: 12.7 mm DShK8		1: 12.7 mm DShK8
Side arms
Quantity
Main	718	592	288
Secondary
MG	1,3308	2,5202	2,3308
Side arms
Armor Thickness (mm)	1327, 30 - 1323, 19 - 1204
Hull Front, Upper	120 - 1606, 1208	120 - 1602	1208
Hull Front, Lower
Hull Sides, Upper	89 - 908, 906	902	89 - 908
Hull Sides, Lower
Hull Rear	606	602
Hull Top	258, 306	20-302	258
Hull Bottom	258	20-302	258
Turret Front	30 - 1008	1002	30 - 1028
Turret Sides		902
Turret Rear		60-902
Turret Top		302
Engine (Make / Model)	V-2-IS3,7, V-2-IS (V2K)8	W-2-IS2 (V-2K)	V-2-IS (V2K)8
Bore / stroke		4 stroke2
Cooling
Cylinders	127,8	V-122	128
Capacity
Net HP	5107, 5134,8	600@2,000 rpm2	5138
Power to weight ratio	11.8 hp/ton6	14.1 hp/ton2
Compression ratio
Transmission (Type)
Steering
Steering ratio
Starter
Electrical system
Ignition
Fuel (Type)	Diesel4,7,8		Diesel8
Octane
Quantity		800 liters2
Road consumption
Cross country consumption
Performance
Traverse	360°
Max speed	23 mph4,8, 24.8 mph3, 24.9 mph7 37 kph6, 40 kph3,7	37 kph2	23 mph8
Cross country speed	15 mph
Road radius	149 miles, 150 miles8, 155 miles3,7 250 km3,7, 130 - 240 km6	150 km2	150 miles8
Cross country radius	130 miles8 110 - 125 km6		130 miles8
Turning radius
Elevation limits
Fording depth	1.3 m6	1.3 m2
Trench crossing	2.5 m6	2.5 m2
Vertical obstacle	1 m6	1 m2
Climbing ability		30 - 36°2
Suspension (Type)
Wheels each side
Return rollers each side
Tracks (Type)
Length
Width	2' 1.63"8		2' 1.63"8
Diameter
Number of links
Pitch
Tire tread
Track centers/tread

Sources:

1. Russian Tanks of World War II Stalin's Armored Might, by Tim Bean & Will Fowler, 2002
2. Russian Tanks and Armored Vehicles 1917-1945, by Wolfgang Fleischer, 1999
3. The Encyclopedia of Tanks and Armored Fighting Vehicles - The Comprehensive Guide to Over 900 Armored Fighting Vehicles From 1915 to the Present Day, General Editor: Christopher F. Foss, 2002
4. Tanks of the World, 1915-1945, Peter Chamberlain, Chris Ellis, 1972
5. Tanks of World War II, Duncan Crow, 1979
6. Russian Armour Volume 1: The IS Tanks IS-1, IS-2, IS-3, Mikhail Baryatinskiy, 2006
7. The Illustrated Guide to Tanks of the World, George Forty, 2006
8. Airfix Magazine Guide 22 Russian Tanks of World War 2, John Milsom and Steve Zaloga, 1977

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