The companion of the T26 was the BT series of "fast" tanks. The T26 was employed promarily by tank units assigned to the support of infantry, while
the BT was assigned to independent tank brigades and in support of cavalry formations. The BT series was based on the American Christie M1930 convertible
tank. Convertible tank were a fad of the 1930's prompted by the lack of reliable tank tracks. Tracks had a short running-life, and were a primary
source of the mechanical breakdowns which afflicted early tank units. The convertible tank skirted thye problem by making it possible to remove the
tracks and run the tank on its roadwheels. This was accomplished by providing a sepcial chain drive to power the rear road wheels while in the wheeled mode.
In this fasion, the tanks could be moved at high speed over roads with no wear on their tracks, and the tankconverted to provide cross-country mobility
once the battlefield was reached; it took about 30 minutes to change a Christie from track to wheel mode.
The two M1930 p[rototypes arrived in the USSR early in 1931, having be shipped from the USA under the guise of agricultural tractors. They were turned over to a new design team at the Kharkov Locomotive Works (Komintern),(KhPZ nr.183) which was already preparing for production on the basis of angineering drawings already sent by Christie.On 23 May 1931, the RVS accepted the new tank for RKKA use as the BT-2 although not even a single prototype had been completed. The BT-1 designation was applied to the American prototypes. The Christie prototypes had arrived without turrets, so the main design change involved the development of turrets and armament combinations. The first three BT-2 prototypes were completed without armament in October and took part in the Moscow parade on 7 November 1931. After trials, KhPZ gegan quantity production of the BT-2 in 1932, manufacturing 396 tanks that year.There were two variants of the BT-2 Model 1932, on armed with a 37mm Model 1930 gun and the other armed with machine-guns. Both vehicles had a DT machine-gun mounted i a ball socket to the right of the m antlet, so the machine-gun armed variant had a total of theree DT machine-guns.The machine-gun variant was not popularly received and subsequent production turned antirely to gun-armed types.
The T3 Tornado and other Christi tanks are the ancestors to the famous Soviet BT series of tanks and thus also influenced the design of the T-34 tank.
This model is the M1931 (model 1931) and was also referred to as the T3. This tank was derived from the earlier M1928. The M1931 was 2 ton's heavier,
better armoured and mounted a turret sporting a 37mm gun.
The US bought 3 of the Christi T3 tanks and the Soviets bought 2.The US didn't proceed further with this design, but the Sovietsdid basing the BT tanks almost directly on the Christi.
Model built by Juraj Korpa
Model built by Brett Mahoney
Model built by Drew Gleason
Model built by Augusto Versiani
Model built by unknown - 1/35 scale - pictures from ww2.mimerswell.com
An Russian modeller informed me that the BT-4 never existed. There was no twin turret BT-4 either. It's a fantasy tank. None of the Russian sources mention it and there haven't been any photographs of it found anywhere.
The BT-4 was a prototype with hull features similar to the BT-3 but with twin turrets replacing the single turret and minor changes in the suspension. (3 prototypes were produced (with partially riveted hull)
1933 Soviet BT-5 Light Tank
1934 Soviet BT-5 Light Command Tank
1934 Soviet BT-5 Light Tank
1934 Soviet BT-5A Light Artillery Command Tank
1934 Soviet BT-5A Light Artillery tank
Kit um360 - BT-5 with cylindrical turret
Built by unknown - 1/35 scale Zvesda - ww2.mimerswell.com
Built by Chema Cabero - 1/35 scale - missinglynx
Model built by Zhenmin Han
Built model by Zhenmin Han
Built model by Juraj Korpa
Was there a BT-8? Who can help me with some pictures and information?
The BT-8 was a major redesign in 1939. It had a sloping front glacis instead of the previous pointed noses. Had a diesel engine installed. The engine was based on a Hispano-Suiza 12Y aircraft engine.1 Hull MG was placed next to the driver. Used at Khalkin-Gol and in Finland.
The BT-8A was a Artillery tank. It had a 76.2 mm 1927/32 tank gun. (Only a test model built)
As the Second World War progressed, the Soviets were fielding better and better tanks. The Finnish Army, on the other hand, had to make due with a
large number of captured tanks, which were for the most part lightly armored and armed. The Finns decided to redesign the BT-7 model 1937 tank. They
constructed a new turret and armed it with British-made 114.3 mm howitzers that had been supplied by the British during the Winter War (Q.F. 4,5 inch
howitzer Mark II, also known as 114 Psv.H/18 in Finland). The Finns constructed 18 BT-42s and these were pressed into service in 1943.
The BT-42 saw action for the first time in 1943, at the Svir River, where it was used to take out enemy pillboxes. The design worked reasonably well against soft targets but was completely unsuitable in the anti-tank role. To counter this, the Finns copied a German-designed HEAT round for the gun, and it was initially thought that it could defeat the sloping armour of the T-34, however, this was not the case.  The BT-42 quickly became very unpopular among its crews. Its mechanical weaknesses could mainly be attributed to the new turret, which apart from giving the tank a high profile also added significant weight to the vehicle, stressing the suspension and the engine.
The BT-42s were used again during the major Soviet offensive in 1944. They were deployed in the defence of Vyborg but were unable to stop the advancing Soviet forces. The BT-42 would suffer heavily during the fighting. At one point, a Finnish BT-42 managed to hit a Soviet T-34 18 times, failing even to immobilize the enemy vehicle. The Finns lost 8 of the 18 vehicles engaged without having made any significant contribution to the fighting. It should however be noted that the Finnish armored units were still mostly comprised of old T-26s, T-28s, and BT-42 AFVs, and that all of these suffered losses during these days (including 25 of the 87 T-26s and a third of all A-20 artillery tractors). German emergency supplies of PzKpfw IVs, StuG IIIs and captured T-34s made it possible for the Finns to replace its aging tanks for more efficient ones. The BT-42 was retired soon after the Vyborg battles and was replaced in the role by German-made StuG IIIs.
In March 1943, the Finnish armoured division suggested that 20 BT-7s should be redesigned into armoured personnel carriers. The Finnish HQ gave its approval sign on 18 May 1943, but limited the number of vehicles to 14. A prototype was designed by removing the turret of a BT-7 and by constructing a wooden platform on top of the chassis. Additional hatches were also installed to allow easier embarking and disembarking of the vehicle. The BT-43 prototype was tested in November 1943, but series production was never started. The single prototype was scrapped in May 1945.
For more info about this variant, visit: (Russian language)
Other version - (descripted as Armoured Personals Vehicle based on the BT-7)
BT-SV II "Turtle" or BTR-based BT?
Comments on alternathistory.org.ua:
It was no APCs and never was. This is a modification of the BT tower, just not visible because of additional vertical bulwarks - BT-SV-2 "turtle.
BTR-based BT?? or BT-SV II "Turtle" - (based on BT-7 Chassis or T-46 chassis?) - T-46 (picture 2)
For more info about this variant, visit: (Russian, English and German language)
Drawings from internet - russiannavy.net - (After research I don't have found reference to this vehicle in any of the major Russian books on AFV’s.)