IS-7 (Object 260) by Recruit Monty

In the Summer of 1945, the design of Object 260 was started, and it was assigned the IS-7 designation.

Zh. Y. Kotin approved the design on September 9, 1945, and in 1946 another variant was designed with the same design number (Obj 260).

The first prototype of Object 260 was assembled on September 8, 1946 and started trials. By the end of 1946, it had driven more than 1,000 km, achieved a maximum speed of 60 kph, and an average speed of 32 kph on broken paved roads.

The second prototype was assembled on December 25, 1946.

The design originally called for a 1,200 hp diesel but such an engine was still unavailable. It was planned to install two V-16 diesel engines, but Factory #77 failed to produce them in time. In the end, TD-30 diesels (converted ACh-300 aircraft diesel engines) were installed on the prototype tanks, which were sufficient but suffered from poor assembly quality.

Additionally, two turrets and two hulls were produced which were used for fire trials. Results of the trials were later used to improve the armour design.

During 1947 tank design was being improved (armour modifications, new gun, variations of machine-gun placements, aiming equipment etc). 12-cylinder naval diesel M-50T with 1,050 hp was used for the new design.

In 1948 four new tanks were produced. Weight 68 tons, easily achieved 60 kph, excellent passability, very easy to control (according to driver's reference). A special experiment was made to see the effects of enemy fire on tank crew. Dogs were put into the tank and the tank was continuously fired at (caliber of guns is not mentioned but judging from the context it seems 128mm German gun was used). Dogs suffered no physical injuries.

In M. Baryatinsky, M. Kolomiets, A. Koschavtsev book Authors mentions that during firetrials both German 128 mm and Soviet 130 mm (S-70) guns were used.

Some data

weight: 66-68 tons (metric)

crew: 5 (TC, gunner, 2 loaders, driver)

lenght: 1148 cm (gun forward)

hull lenght: 738 cm

width: 340 cm

height: 243-248 cm

ground clearence: 50 cm

armament

130 mm S-70 gun

14,5 mm KPVT (coax)

14,5 mm KPVT (AA, remote control)

2 x 7,62 mm SGMT (coax)

2 x 7,62 mm SGMT (fixed on hull, firing ahead)

2 x 7,62 mm SGMT (fixed on turret, firing back of turret)

ammo

25 x 130 mm rounds, 1000 x 14,5 rounds, 6000 x 7,62 rounds

armour

hull: 150 mm (sloped)

turret: 210 mm

performance

engine: M-50T 1050 HP (or 1250 HP, depends on source) diesel

power/mass: ~15,5 HP/t

max. speed: 60 km/h

range: 300 km

fuel capacity: 1300 litres

- fuel tanks were made of rubber

- automatic fire extinguishers system

130 mm S-70 L/54 fired 33.4 kg rounds with a muzzle velocity of 900 m/s.

Incidents during trials: One tank had a weak weld which broke when a shell ricocheted from the tank. An engine of another tank, which had already worked it's resource, suddenly ignited and the automatic fire-extinguishers failed to stop the fire. Crew left the tank and it burned completely.

In 1949, it was planned to produce 50 tanks on Kirov's tank factory. However not a single tank was produced due to conflicts between the military (who demanded to reduce tank's weight to 50 tons while keeping all other parameters intact) and the factory.

Source: M. Baryatinsky, M. Kolomiets, A. Koschavtsev. "Heavy Soviet Post-War Tanks", "Armour Collection #3, 1996".