IS-4

Development of the IS-4 started in November 1943 with the purpose of improving upon the IS-2 and incorporating captured enemy technology. This created a blend of IS-2 features and unique features not found in other Soviet tanks. The IS-2's stepped front plate was judged to be a weak point and made into a single glacis with additional armor for the driver. This was in order to accomplish the IS-4's design parameters which included the ability to defeat the German 8.8 cm Pak 43 anti-tank gun.[3] The side hull of the IS-4 is a simple angular step instead of angling out like the IS-3. The right side of the tank was fitted with clamp rings to carry an unditching log.[3] The driver's position was described as cramped, though the writer of the review is typically taller than tankers of the time.[2]

The IS-4 track system is based on the IS-2 with an additional set of cast road wheels bringing the total to 7 pairs on a torsion bar suspension system. The IS-4 has bump stops similar to other torsion bar systems, but notably does not have shock absorbers to stop rocking, relying instead on mass. The track is similar to others in the IS series, except it has a center guide on every track link instead of alternating ones. Each track is held in place by a single pin with a clip and washers. In the rear, each fender was able to hold two external 90 liter fuel tanks side by side. The rear also could hold an "MDH" ("Small Naval Generator") smoke generator which was equipped with a quick detach under the control of the driver who could activate it from inside the tank.[3]

The IS-4 had a rear transmission system and a rear gun travel lock.[3] The engine was a V12 which was an improvement over the V2 and fitted with a newly designed transmission and steering system capable of neutral steering.[2] The IS-4 has two circular radiator fans externally identical to German World War II tanks, though internally different. It had two internal fuel tanks, the left 295 liters, the right 115 liters.[3]

The turret has features similar to the IS-3, a large access port to remove the cannon and similar hatch layout. The commander was originally going to have a rotating cupola similar to a late model M4 Sherman but this seems to have not been implemented.[3] Unlike the IS-3, the IS-4 featured a dedicated bustle rack for ammunition in the rear of the turret. The IS-4 turret, with powered traverse, was noted by Nicholas Moran to be larger and roomier than the IS-3 turret, allowing for more ammunition for the coaxial machine gun.[2] The IS-4 might have had an intercom system on the back of the turret to allow mounted infantry to talk with the tank crew.[3]

Production started in 1946, too late for World War II. It was found to be overweight and its original purpose (to fight against Germans) was over. Furthermore, the IS-3 was already in production. For these reasons less than 250 were built.[2]

Later in the 1950s a side skirt was added, however in the 1960s they were retired, with some serving on the Chinese border as pillboxes.[2]

 Soviet Union

• Soviet Army: Accepted into service on 29 April 1946[1]

• Kubinka Tank Museum, Russia.[3]

• IS tank family
• KV-1
• T-10
• ISU-122
• ISU-152
• List of Soviet tanks