BT-5-IS

In 1934, Voroshilov ordered the 4th Tank Regiment to create a new "wheeled-tracked propulsion unit for the BT tank, with which it can be turned into an even more formidable fighting vehicle." This task was entrusted by Iona Yakir to a group of engineers led by Nikolai Tsyganov . After 4 months of work, by April 1935, drawings and a 1/5 full-size model of the BT tank were ready with a new mover that had 3 pairs of driving (2, 3, 4) and steered (1, 2, 4) wheels. When developing this project, only the chassis of the BT-2 and BT-5 tanks was affected. A report was sent on completion of work in a letter to Stalin and Voroshilov . According to Voroshilov’s personal order, the necessary funds were allocated for the production of BT-IS, a place at Kharkov Tank Repair Plant No. 48, and a BT-2 tank. In June 1935, began testing the car, which lasted until the fall. Voroshilov in 1936 issued an order for the manufacture of 10 BT-IS tanks based on the BT-5 tank.

In March - June 1937, three BT-ISs, after making changes in Plant No. 48 based on the results of the Kharkov - Moscow run, underwent military tests in the vicinity of Kharkov . Its main structural difference was the presence of three pairs of wheel drive wheels, which made it possible to use more than 75% of the tank’s mass as the grip weight, the presence of a special mechanism to equalize the speeds on wheels and tracks, and a significant increase in the capacity of gas tanks. The engine, main clutch, gearbox, on-board clutches, brakes, control drives, front-wheel steering with wheels, the turret and weapons remained unchanged.

During the tests, tanks traveled from 1,500 to 2,500 km, BT-5-IS showed significantly greater cross-country ability and survivability in comparison with BT-5 and BT-7 . Despite the identified shortcomings - weakness of the synchronizer gears, overloading of the rubber of the rear wheels, failure of the threads of the rods of vertical candles and poor access to the additional transmission - the army commission decided to take the BT-IS into service. The head of the ABTU RKKA was ordered to manufacture in 1937 an installation batch of 5 BT-IS vehicles, on which it was planned to install inclined side armor and eliminate the identified deficiencies, and in 1938, factory number 48 was to produce 300 BT-IS. Until the end of 1937, only one such machine was made based on the BT-5 , which had additional inclined sides of 6 mm armor. In connection with the arrest in early 1938 of Tsyganov and other design bureau members, work on the BT-5-IS project was discontinued. ^[one]

By the fall of 1938, Plant No. 48 produced in a single copy an improved model of the BT-5-IS tank with inclined armor plates, the tests of which were carried out from November 1938 to January 1939. The car was different from the BT-5-IS tank of the 1936 model, the capacity of the fuel tanks was reduced to 570 liters and the installation of a four-stroke, twelve-cylinder V-shaped M-17 T carburetor engine with a power of 400 hp .. ^[2]

In its final form, the BT-IS tank was a modernized BT-5 vehicle.
The hull underwent partial alterations due to the installation of new struts, an increase in the distance between the side walls, the installation of a stern gas tank and the reservation of the final drive housing. The drive shaft of the final drive, the balancers of the track rollers, the suspension, the drive wheels of the caterpillar track have changed. A number of new wheel drive transmission mechanisms were introduced: a synchronizer, a corner box, upper boxes, cardan shafts, a drive wheel drive wheels, a synchronizer shift drive. The fuel supply system was redone from three gas tanks in turn to power from each tank individually.
The rotation to the transmission of the wheel drive was transmitted from the conical pair of the drive shaft of the final drive to the synchronizer. From it through a semi-rigid gear coupling to the shaft of the corner box, and then through the couplings and the intermediate roller to the shaft of the first upper box. From the latter, the rotation was transmitted sequentially to the second and third upper boxes, from the upper boxes using cardans and composite cardan shafts to the drive of the drive wheels and from it to the wheels themselves. The type and design of the BT-5-IS suspension remained unchanged compared to the BT-5 except that the guitar was replaced with a rear balancer. ^[one]

• M.V. Pavlov, I.V. Pavlov, I.G. Zheltov "Tanks BT" (series "Military Museum"), Moscow, Exprint, 2001
• M. Baryatinsky, M. Kolomiyets “Light tanks BT-2 and BT-5” (“Bronekollektsiya MK”, 1996-01)
• Domestic armored vehicles 1905-1941. Volume I. Publishing center "Exprint". 2002
• Tanks of the world. Ed. "Rusich." Smolensk, 2005