Introduction

The IS-4 is an early Cold War era heavy tank of Soviet origin. The IS-4 was the heaviest of the Soviet heavy tanks to see serial production. The much heavier IS-4 replaced the IS-3 on the production line. Production figures were low due to the demand for civilian agricultural tractors produced at Chelyabinsk. In addition, production quality was low and up to 60% of vehicles produced were rejected by the Soviet army.

Design

The design program that led to the IS-4 coincided with the IS-3. The goal of the design program was to incorporate useful design elements from captured German tanks during World War 2 in the domestic IS-2 design. The most notable feature are the two cooling radiators on the engine deck, similar to the Panther tank.

Firepower

The IS-4 was intended to have an improved gun over the IS-3. This was to be the 100mm S-34, but mounting the gun and storing the ammunition proved difficult. Only 12 100mm rounds could be carried. To meet production deadlines the 122mm D-25T from the IS-2 and IS-3 was retained. A total of 30 shells are carried. Two 12.7mm DShKM heavy machine guns are fitted. One as coaxial armament and one on the turret roof for self-defense. The main gun is not stabilized and is manually loaded. Rate of fire is low at 2 to 3 rpm. Maximum direct fire bombardment range is 5 km.

Protection

The IS-4 has the legacy of being the most heavily armored Soviet tank ever in serial production. Even though the armor layout is less optimal than the IS-3 or T-10, the protection level is better due to its thickness. Unlike either IS-3 or T-10 the armor remains quite thick are the rear. This makes it more suitable in the breakthrough role and not limiting it to long range bombardment. There is no NBC system and only the IS-4M upgrade added two smoke grenades.

Mobility

Mobility was the weak point of the IS-4. Especially the reliability of the gearbox and drive train. The power-to-weight ratio is low, but still a speed of 42 km/h can be achieved. The IS-4M was fitted with an increased performance gearbox. The range on road and in the field is rather low, due to the high weight and limited fuel capacity.

Users

IS-4 officially entered service in 1946, with only a handful vehicles produced by that time. Of the over 230 vehicles produced many immediately went into storage. In 1951 a small batch of IS-4M was produced and all existing IS-4 were brought up to that standard. Several heavy tank regiments stationed in Belarus used the IS-4M until the early 1960's. From that moment all IS-4M were sent into long term storage in the Transbaikal and Primorye regions to serve mobile pillboxes in fortified areas in case of war with China.

The IS-4 looks more akin to the IS-2 than its IS-3 predecessor. The front hull is similar to the late production model IS-2 and the turret is not dome shaped like the IS-3. In many ways the IS-4 design was a step backwards from the IS-3, although superior in armor thickness.

Interestingly, the IS-4 has a shorter hull than the IS-3 while having a 7th set of roadwheels either side. This is achieved by having the roadwheels closer together and having a less sharply pointed nose section on the hull.

The IS-4M upgrade was to bring the IS-4 up to a functional level and to a similar equipment standard as the IS-3M. The main upgrade is a more reliable transmission, improving the reliability significantly. The IS-4M upgrade was applied throughout 1951 to existing vehicles, as well as a new production run of only 25 vehicles.

Similarities with the IS-3M upgrade include the rubber side skirts, passive infrared night vision for the driver, external fuel drums and updated intercom and radio sets. Unlike the IS-3M upgrade no new engine was fitted.