IS-1

IS-1

KV-85

IS-2

IS-1

KV-85

IS-2

USSR

III Rank

Battle rating:

AB	RB	SB
5.7	5.7	5.7

Class:

Heavy tank

Research:40 000

Purchase:135 000

Show in game

Description

The IS-1 is the first variant of the IS heavy tank family. The new IS-1 was intended to overcome the lack of firepower and protection issues of the KV series with a whole new sloped hull design. This was a strong armour design intended to deflect or withstand projectiles from all sides. The only major design requirement was that the weight not surpass that of the interim KV-85. The new armament was the same as the KV-85, an outstanding 85 mm D-5T tank gun with significantly higher range and muzzle velocity than prior Soviet heavy tanks. The turret was also identical to that of the KV-85, with three crews. The drivetrain was similar to that of the KV-85, with enormous tracks supported by three pairs of double return rollers and six double-tired wheels suspended by massive torsion arms. Extra fuel tanks were fitted to the rear of the hull, as with all earlier heavy tanks, and massive mudguards housed storage boxes. The engine was replaced with a new V2-IS 12-cylinder diesel engine producing 520 horsepower. The typical top speed was 37 km/h, and the practical range was only 150 km. Chelyabinsk Kirov Plant was responsible for the IS-1 manufacturing, and the first IS-1 rolled off the line in October 1943, but production was halted in January 1944 as the IS-1 was swiftly replaced by the all-round better IS-2. As a result, only 200-207 units were produced in total.

Introduced in the Closed Beta Test for Ground Forces before Update 1.41, the IS-1 has slightly superior hull protection than the interim KV-85. Tank shells can be easily deflected at long ranges thanks to a unique sloped frontal hull. However, the hull's lower front armour plate remains a weakness, and nearly all opponents in its rank are able to penetrate it. The visual characteristics of the IS-1 are also comparable to those of the KV-85. Players who have previously played the KV-85 should have little difficulty adjusting to this vehicle. The IS-1, unlike its predecessor, was developed with the purpose of breaching enemy heavy defences and engaging hostile armoured vehicles in mind and, as such, has thicker sloping armour, a slightly longer chassis, a more powerful 85 mm D-5T tank gun, and a larger, rounder turret.

General info

Survivability and armour

Armourfront / side / back

Hull120 / 90 / 60

Turret100 / 100 / 100

Crew4 people

Visibility102 %

The IS-1 has an excellent armour overall: its strong well sloped turret can bounce a few shells with an improved hull compared to the KV-85. The tank's heavy armour has similar properties of its previous KV-1 line, but the introduction of sloped armour on the front plate and turret mantlet can allow operators to withstand a significant amount of damage at most ranges, especially when armour is angled. The unique curvature of the upper front portion of hull armour can sometimes effectively bounce incoming shells from high penetrating cannons. It is a trait that remains in the IS-2 series. A huge and easy to hit weak spot is the commander's cupola that will easily knock out the turret crew if penetrated by APHE shells. It is impossible to angle the tank due to the unique curvature of the upper front portion of hull armour; while it serves to be an advantage when facing directly forward, any angling will be counterproductive, turning the upper front portion of the hull armour to a major weak spot. Taking too much ammunition will risk easy explosion from penetrating enemy shells due to the widespread storage of tank ammunition around the hull and in turret.

Armour type:

• Cast homogeneous armour (Front hull, Turret)
• Rolled homogeneous armour (Rear hull, Gun mantlet)

Armour	Front	Sides	Rear	Roof
Hull	120 mm (35°) Front plate 60 mm (75°) Front glacis 100 mm (28-36°) Lower glais	100 mm (11-27°)Top front 90 mm (11°) Top rear 90 mm Bottom	60 mm (48°) Top 60 mm (35°) Lower	30 mm
Turret	100 mm (0-89°) Turret front 100 mm (4-59°) Gun mantlet	100 mm (19-21°)	100 mm (2-36°)	30 mm 35 mm Turret hatches
Cupola	90 mm	90 mm	90 mm	35 mm

Notes:

• Suspension wheels are 20 mm thick and tracks are 30 mm thick.
• Though the front plate is 120 mm thick, it is not very sloped in comparison to the front glacis. Despite front glacis, 60 mm thickness, slope effect up to ~130 mm and ricochet chances improve protection.

Mobility

Speedforward / back

AB40 / 16 km/h

RB and SB38 / 15 km/h

Number of gears8 forward

2 back

Weight44.0 t

Engine power

AB992 hp

RB and SB520 hp

Power-to-weight ratio

AB22.5 hp/t

RB and SB11.8 hp/t

The IS-1 has a good overall mobility and maneuverability for a heavy tank. Its respectable reverse speed allows for getting back to cover fast enough to avoid retaliatory fire. The mobility can be sluggish when attempting to turn or steer from previous stationary position, it is advised to build up speed first.

Game Mode	Max Speed (km/h)		Weight (tons)	Engine power (horsepower)		Power-to-weight ratio (hp/ton)
	Forward	Reverse		Stock	Upgraded	Stock	Upgraded
Arcade	40	16	44	671	827	15.25	18.8
Realistic	38	15		460	520	10.45	11.82

Modifications and economy

Repair costBasic → Reference

AB2 010 → 2 486

RB2 176 → 2 691

SB3 022 → 3 738

Total cost of modifications34 400

67 200

Talisman cost1 300

Crew training39 000

Experts135 000

Aces550

Research Aces390 000

Reward for battleAB / RB / SB

90 / 140 / 150 %

154 / 154 / 154 %

Modifications

Mobility	Protection	Firepower
Tracks Research: 1 700 Cost: 3 300 105 Suspension Research: 1 900 Cost: 3 700 120 Brake System Research: 1 900 Cost: 3 700 120 Filters Research: 2 200 Cost: 4 300 140 Transmission Research: 5 600 Cost: 11 000 350 Engine Research: 5 600 Cost: 11 000 350	Improved Parts Research: 1 700 Cost: 3 300 105 Improved FPE Research: 1 900 Cost: 3 700 120 Crew Replenishment Research: 2 200 Cost: 4 300 140	Horizontal Drive Research: 1 700 Cost: 3 300 105 85mm_APHE_ammo_pack Research: 1 700 Cost: 3 300 105 Adjustment of Fire Research: 1 900 Cost: 3 700 120 Elevation Mechanism Research: 2 200 Cost: 4 300 140 85mm_APCR_ammo_pack Research: 2 200 Cost: 4 300 140

Armaments

Main armament

85 mm D-5T cannon

Ammunition59 rounds

Reloadbasic crew → aces

9.6 → 7.4 s

Vertical guidance-5° / 25°

The 85 mm D-5T is a very strong and potent cannon for this BR that can deal with a range of enemies with relative ease; careful aiming is required against Tiger Is and Panthers. The poor gun depression makes fighting in mountainous terrain very difficult.

85 mm D-5T					Turret rotation speed (°/s)					Reloading rate (seconds)
Mode	Capacity	Vertical	Horizontal	Stabilizer	Stock	Upgraded	Full	Expert	Aced	Stock	Full	Expert	Aced
Arcade	59	-5°/+25°	±180°	N/A	11.33	15.68	19.04	21.06	22.40	9.62	8.51	7.84	7.40
Realistic					8.33	9.80	11.90	13.16	14.00

Ammunition

Penetration statistics
Ammunition	Type of warhead	Penetration @ 0° Angle of Attack (mm)
		10 m	100 m	500 m	1,000 m	1,500 m	2,000 m
BR-365K	APHE	148	143	126	106	90	77
BR-365A	APHEBC	135	133	124	114	104	95
BR-365P	APCR	195	187	154	122	96	76
O-365K	HE	19	18	17	16	15	14

Shell details
Ammunition	Type of warhead	Velocity (m/s)	Projectile mass (kg)	Fuse delay (m)	Fuse sensitivity (mm)	Explosive mass (TNT equivalent) (g)	Ricochet
							0%	50%	100%
BR-365K	APHE	792	9.2	1.2	14	77	47°	60°	65°
BR-365A	APHEBC	792	9.2	1.2	14	164	48°	63°	71°
BR-365P	APCR	1,050	4.99	-	-	-	66°	70°	72°
O-365K	HE	785	9.54	0.2	0.1	741	79°	80°	81°

Ammo racks

Ammo racks of the IS-1

Full ammo	1st rack empty	2nd rack empty	3rd rack empty	4th rack empty	5th rack empty	6th rack empty	Visual discrepancy
59	55 (+4)	37 (+22)	27 (+32)	21 (+38)	11 (+48)	1 (+58)	No

Notes:

• As they are modeled by sets of 2, shells disappear from the rack only after you've fired both shells in the set.
• Turret empty: 37 (+22) shells.

Machine guns

7.62 mm DT machine gun (coaxial)

Ammunition2 520 rounds

Belt capacity63 rounds

Reloadbasic crew → aces

10.4 → 8.0 s

Fire rate600 shots/min

The IS-1 has no roof-mounted heavy machine gun lime they are found in later Soviet heavy tanks and SPGs to defend against incoming enemy aircraft. The only machine gun available is a 7.62 mm coaxial MG. Useful for taking out unarmored trucks and exposed crew.

7.62 mm DT
Mount	Capacity (Belt)	Fire rate	Vertical	Horizontal
Coaxial	1,890 (63)	600	N/A	N/A

Usage in battles

As the tank's design purpose suggests, the IS-1 is a heavy tank built with an emphasis on engaging hostile armoured vehicles as well as a breakthrough tank. It has a relatively similar playstyle compared to the previous KV-85 tank, reducing the learning curve. The fast reloads speed of the 85 mm gun (on par with its T-34 and KV-85 mounted sisters) also allows it to be an effective brawler in close quarters combat against multiple targets. When encountering better-protected targets, the IS tank (although equipped with the same type of cannon) has access to APCR rounds to better deal with heavier opponents, something the KV and T-34 models lack.

Although classified as a heavy tank and an upgraded improved design over the KV predecessor, the tank is not invulnerable. The vehicle's armour thickness is quite effective in its class. Unlike its Tiger rivals and KV predecessors, the IS-1 has better or equal thickness armour on almost all sides except the rear hull and is sloped increasing the chance of ricochet and damage reduction when struck. Of note is the large turret and exposed turret mount which is commonly targeted at engaging hostile vehicles from the front. Armaments and ammunition options aside, the IS tank can perform similarly if not better at engaging targets than the common T-34, albeit with more satisfactory armour protection, able to allow users to lead a charge from the front with relative confidence or provide fire support from the sides or rear. This tank is quite sufficient in holding its own on the battlefield in many situations where a lighter vehicle cannot.

Another significant note of this vehicle is its considerably fast reverse rate, the highest of its Rank and Battle-Rating for the nation's faction, topping at 17 km/h. During situations where close-quarters engagement is expected, an unorthodox strategy can be utilized when the operator of the IS tank re-positions the vehicle 90 degrees and drive in reverse towards the enemy. By driving in reverse with the rear-facing the opposition, the engine blocks make a crude yet somewhat effective shield and protecting the more delicate crew. As the fuel tanks are mostly stored at the front on the left and right side of the driver's station, the risk of fire and fuel-tank explosion is reduced significantly (but not completely eliminated) and thus, the tank is able to resist even the most powerful of shots. Be aware that more experienced players may attempt to instead fire at the more exposed turret of the IS tank and instantly knocking out the crew with a common APHE penetrating the shell.

When engaging the common Tiger tank and Panzer IV models, each of these vehicles retains the design flaw of 90 degree flat armour plates on the front and sides of each respective vehicle. The IS-1's 85 mm cannon should have little no difficulty in penetrating this and destroying the opposition's vehicle in a single shot if this weakness is exploited. The Panther and occasional Tiger II models are more considerably dangerous and difficult to dispatch when encountering them head-on due to the thicker and sloped armour of which the 85 mm cannon of the IS-1 cannot penetrate. In head-on engagements, operators of this vehicle should note to precisely target the right and left side turret mantlet of each respective vehicles instead. Time expended in attempting to find a penetration confirmation indication on the cross-hair when inspecting the sloped front plate is time wasted and instead, should be diverted on precise targeting of the mantlet. Other more common tanks such as opposition USSR KV, IS and T-34 models are usually less of a concern than the common Panther tank, as most of these respective tanks also inherit the weakness of somewhat slopped frontal chassis and turret armour which can be easily penetrated even from significant distances with a precise aim.

If you are to apply bushes onto the IS-1, consider putting most of them on upper frontal hull and the curved sides next to it. This is because that quite some opponents will automatically target the curved armour, knowing that area is a common weak spot when the IS is angling. By covering up the hull front and the curves, the IS's frontal hull will now look flatter, somewhat resembling the hull of an IS-2 1944. This will cause some confusion and delay the enemy's reaction & aiming time, as they now cannot directly see where your curved armour is, gifting you a precious few seconds before they open fire. For any leftover bushes, the turret front and the lower front plate are also good spots to put them on.

Pros and cons

Pros:

• Good armour
• Extremely durable against in down-tiered battles (when encountering lower rank M4 Shermans, Valentines, Pz.IV etc.)
• Re-positioning of fuel tanks reducing chances of fires.
• Good mobility with a fast reverse speed
• Sufficient firepower
  • High rate of fire
  • Ability to fire APCR
• Player skill compatibility between older and newer KV and IS models

Cons:

• Large tank (slightly longer than the KV-1)
• Difficult to angle armour due to weaker hull cheeks
• Turret cheeks are easy to penetrate even at long distance
• Commander cupola is a big weak spot
• Poor gun depression (a common trait in all Soviet tanks)

History

Development

The start of the development for a new heavy tank in the Red Army came from the many criticisms of their current heavy tank, the KV-1. The KV-1 had poor mobility and a lack of firepower and armour advantage over the standard T-34, plus the KV-1 was more expensive to produce for no real advantage. Attempts to remedy this problem produced the KV-1S and the KV-85, which tried to make the KV-1 more mobile, more ergonomic, and have better firepower. Though they were improvements over the original KV-1 design, it was already determined that the KV-1 designs are to be replaced by a new heavy tank design and the newer KV-1 developments were to be interim designs until the heavy tank development is complete.

The heavy tank project, code-named Object 237, had its basis from the cancelled KV-13 program and was restarted from the discovery of the Tiger I after one was captured in Leningrad, thus it began in January 1943. However, despite the ensuing development, the intense tank fighting in 1943 in Kursk and ensuing operations forced the Object 237 to see action early, with its turret used on the KV-85, which itself was built atop the KV-1S hull. The turret mounted the new 85 mm D-5T gun and would be a great firepower advantage enjoyed by the Soviet tank forces as it gave them a heavy tank with comparable firepower to the Tiger I's 88 mm cannon. At the end of 1943, the Object 237 project was finished and was accepted into service as the IS-85, or the IS-1, named after Iosef (Joseph) Stalin, the current leader of the Soviet Union during World War II, putting an end to the Voroshilov (KV) line of tanks. The IS-1 began to be delivered in October 1943 and went into service in the same month. The IS-1 stayed in service until January 1944, when its production also ended with about 200 units produced.

Combat usage

The IS-1, like the KV-85 before it, was a great assist to the Soviet tank forces, giving them a heavily armoured tank with a great 85 mm gun that could defeat most of the German tanks in service except their heaviest ones such as the Tiger I and the Panther tanks. The IS-1 was issued to Guards Heavy Tank Regiments for service, most notably the 1st, 8th, and 13th Guards Heavy Tank Regiments which saw service in Ukraine and Slovakia. Within a standard IS-1 issue tank, there were often 59 85 mm rounds and 2,500 rounds for the three DT machine guns, which allowed it to have both superior armaments and capacity compared to the standard Tiger I.

The IS-1 had a short-lived production due to advances in Soviet tank technology. Their standard T-34 medium tanks were upgraded with the same 85 mm gun on the IS-1 into the T-34-85. The lack of firepower advantage the IS-1 now presented due to this upgrade prompted an up-gunning of the IS tank with a much bigger gun. After further development in late 1943, the IS-1 evolved into the IS-2, which has the larger and much more powerful 122 mm A-19 gun.

Archive of the in-game description

The IS-1 was developed in the spring and summer of 1943 by factory No. 100's design bureau led by Z.Y. Kotin. The tank's hull design and overall layout were taken from the previously developed experimental KV-13 tank. The main priority was creating reliable protection against the German 88 mm Flak 18 artillery cannon and making considerable mobility improvements by reducing the tank's mass and introducing a new epicyclic gearbox. The results of battles in 1943 revealed the need for a new heavy assault tank to replace the outdated mass-produced KV tanks. The prototype, designated IS, was built, tested and put into service in the Red Army in July-September 1943. Thanks to its new gearbox and the more streamlined placement of its strengthened armour, the new tank possessed superior mobility. The IS's tight layout in its habitable section meant that a fifth crew member - the gunner/radio officer - would not fit inside. His duties were distributed between the commander and the driver. Three crew were housed in the turret: the tank commander and the driver worked to the left of the gun, and the loader to the right. A command cupola with 82 mm thick vertical armour was installed in the tank's turret, and its hull had a hatch leading to the underside of the tank to allow the crew to evacuate in an emergency. The IS-1 was armed with an 85 mm D-5T Mod. 1943 tank cannon and three machine guns. It entered mass production in October 1943 at the ChKZ factory. In total, 130 of them were built. The IS-1 was deployed in battles from February 1944 up to and including the winter of 1945. The results of these battles led to the conclusion that the armament and armour of the new tank were not equal to those of German heavy tanks. At that time, it was recommended that the shape and armour of the frontal hull be changed and the tank's armament upgraded immediately.

Media

Skins

• Skins and camouflages for the IS-1 from live.warthunder.com.

Videos

The Shooting Range #61 - Pages of History section at 09:02 discusses the IS-1.

The IS Family - War Thunder Official Channel

See also

Links to the articles on the War Thunder Wiki that you think will be useful for the reader, for example:

• reference to the series of the vehicles;
• links to approximate analogues of other nations and research trees.

External links

References

Chelyabinsk Tractor Plant (Челябинский тракторный завод)
IFVs
BMP-1	BMP-1
Heavy Tanks
KV	KV-85 · KV-122
IS-1/2	IS-1 · IS-2 · IS-2 (1944) · IS-2 "Revenge" · IS-2 No.321
T-10	T-10A · T-10M
Other IS Tanks	IS-3 · IS-4M
Tank Destroyers
KV Derivatives	SU-152
IS Derivatives	ISU-152 · ISU-122 · ISU-122S · Object 268
Export
IS-2	␗IS-2 · IS-2 No.402 · ␗IS-2 (1944)
ISU	␗ISU-152 · ␗ISU-122
IFVs	SPz BMP-1
See Also	Leningrad Kirov Plant