More than 50 different modifications and experimental vehicles based on the T-26 light infantry tank chassis were developed in the USSR in the 1930s, with 23 modifications going into series production. The majority were armoured combat vehicles: flame tanks, artillery tractors, radio-controlled tanks (teletanks), military engineering vehicles, self-propelled guns and armoured personnel carriers. They were developed at the Leningrad Factory of Experimental Mechanical Engineering (from 1935 known as the Factory No. 185 named after S.M. Kirov) by talented Soviet engineers P.N. Syachentov, S.A. Ginzburg, L.S. Troyanov, N.V. Tseits, B.A. Andryhevich, M.P. Zigel and others. Many Soviet tank engineers were declared "enemies of the nation" and repressed during Stalin's Great Purge from the middle of the 1930s. As a result, work on self-propelled guns and armoured carriers ceased in the USSR during that time. T-26 light tanks were also modified into armoured combat vehicles in the field during wartime.
Flame-throwing (chemical) tanks
Flame-throwing tanks formed around 12 per cent of the series production of T-26 light tanks.Baryatinskiy (2003), p. 22 It should be mentioned that the abbreviation "OT" (Ognemetniy Tank which stands for Flame-throwing Tank) appeared only in post-war literature; these tanks were originally called "KhT" (Khimicheskiy Tank which stands for Chemical Tank), or BKhM (Boevaya Khimicheskaya Mashina; Fighting Chemical Vehicle) in the documents of the 1930s. All chemical (flame-throwing) tanks based on the T-26 chassis (KhT-26, KhT-130, KhT-133) were designated BKhM-3. The vehicles were intended for area chemical contamination, smoke screens and for flame-throwing.
The TKhP-3 chemical equipment for smoke screens and chemical contamination was developed in 1932. This equipment could be easily installed on any T-26 light tank and was produced by the "Compressor" Factory, (introduced for smoke screening as the TDP-3 from summer 1934; 1,503 such sets were produced to the end of 1936).
KhT-26 (OT-26) — Flamethrower variant developed in 1933. Based on the twin-turreted T-26 mod. 1931 tank but using a single turret armed with a flamethrower, the second turret was removed. KhT-130 (OT-130) — Flamethrower variant of model 1933, using a larger 45 mm gun turret (main gun was replaced with a flamethrower). KhT-133 (OT-133) — Flamethrower variant of model 1939 (main gun was replaced with a flamethrower). KhT-134 (OT-134) — Flamethrower variant of model 1939, with 45 mm gun intact and hull-mounted flamethrower. Prototype only.
Combat engineer vehicles
Kolomiets (2007), pp. 90-95Baryatinsky (2003), pp. 39-40Kolomiets (2003), pp. 14-21 (ST stands for saperniy tank or "engineer tank") — engineer tank; a bridge-laying tank based on the twin-turreted T-26 mod. 1931 chassis. According to the "System of armoured engineering armament of the Red Army", the ST-26 was developed by designers from the Academy of Military Engineering (chief engineer of the project - Gutman) in the beginning of 1932. The ST-26 had only one shortened turret in the middle of the hull armed with a DT tank machine gun with 1,008 rounds; arc of fire was 211°. Special equipment consisted of a metal tracked bridge long and weighing , supports for the bridge (a front frame with two forks and two guiding rollers, lower forks with a hoisting mechanism and a roller, a rear frame with mounts and two rollers) and a cable winch (driven by the tank engine with the use of the reversing gear) inside the vehicle. The ST-26 was intended to provide for crossing of trenches and streams wide and barriers up to high by T-27, T-26 and BT light tanks: the bridge had a maximum load rating of . The bridge could be laid with the help of the cable winch in 25–40 seconds without crew exit; the raising operation took 2-3 min and a commander needed to come out from the vehicle in order to control the process. The ST-26 with its cable system for bridge laying was tested in the summer of 1932.
Additional variants of the ST-26 (with a sliding system of bridge laying and with a tipping system of bridge laying) were also tested from 1932. The first had a massive guide frame and a special boom (the bridge could be laid in 3 min 20 sec, the raise operation took 6-7 min), while the second was equipped with a special swinging-boom with a rack-and-pinion drive. All three variants of the ST-26 participated in military maneuvers of the Leningrad Military District in the summer of 1933; subsequently series production of the ST-26 with a cable system of bridge laying was begun as it proved to be more reliable and less complicated to maintain. The Defence Committee of the USSR ordered the production of 100 ST-26 to the end of 1933, but only 44 vehicles were assembled by the Factory No. 174 by 1934, and 20 in 1935. The delay was attributed to the manufacture of the metal bridges, carried out by the Gipstalmost Factory and several workshops using semi-handicraft techniques.
Specifications: weight - ; crew - 2 men (commander and driver); speed - ; range - .
The Armoured Engineering Section of the Red Army's Research Institute of Engineer Equipment (NIIIT RKKA) in co-operation with the Gipstalmost Factory developed an improved engineer tank at the end of 1936, with a lever hydraulic system of bridge laying (similar to the UST-26, see below) and a small turret of new design. The bridge could be laid in 45 sec and the raise operation took 1.5 min (both processes did not require crew exit). The vehicle was assembled by the Podolsk Machine Factory named after S. Ordzhonikidze in July 1937, and was successfully tested at the NIIIT Proving Ground (85 bridge layings were performed and 70 light tanks passed over the bridge). This ST-26 prototype was also tested at the Kubinka Tank Proving Ground, and participated in military exercises of the Leningrad Military District in 1938. A decision was made in 1939 to produce a batch of engineer tanks with the lever hydraulic system, but the Podolsk Machine Factory could assemble only one. The Stalingrad Tractor Factory probably also produced two such vehicles the same year.
An experimental multispan bridge was developed in 1934 which allowed for the coupling together of three or more ST-26 bridges, using special automatic grips in the end of each bridge section. The multispan bridge employed 250 kg metal columns high and was intended for crossings by T-26 and BT light tanks of water obstacles up to wide and deep. The launching of each bridge section took 20-30 min. The bridge had no development after testing.
Engineer Alexandrov from the Research and Technology Division of the Red Army's Engineer Directorate (NTO UNI RKKA) developed a wooden tracked bridge long. The bridge was mounted on standard T-26 light tanks as well as on ST-26 engineer tanks and could be laid in 30-60 sec without crew exit. Trials carried out in July–August 1934 were successful and 20 such bridges were issued to the armed forces.
Seventy-one ST-26 engineer tanks were produced in 1932–1939, including experimental vehicles: 65 ST-26 with a cable-laid bridge system, 1 ST-26 with a sliding bridge, 1 ST-26 with a tipping bridge, 2 UST-26 and 2 ST-26 with a levered bridge-laying system.
Ten ST-26 engineer tanks were used on the Karelian Isthmus during the Winter War (9 with a cable system and 1 with a lever system); they were included in engineer groups for obstacle clearing that were established in each tank brigade during the war. Three ST-26 tanks of the 35th Light Tank Brigade had the most success (in particular they launched two bridges over a trench and then an antitank ditch for a tank battalion during an assault on the fortified High Point 65.5 (Hottinen area) of the Mannerheim Line on February 18, 1940). The ST-26 with the lever system of bridge laying demonstrated good results and that vehicle was used quite actively during the Winter War, while tanks with the cable system were less reliable and had limited use. There were no losses of ST-26 engineer tanks during the Winter War.
Tank units of the Red Army had 57 ST-26 engineer tanks on June 1, 1941: 9 in the Far Eastern Front, 26 in the Moscow Military District, 2 in the Leningrad Military District, 2 in the Kiev Special Military District, 8 in the Western Special Military District, 1 in the Volga Military District, and 9 vehicles were in military supply depots. From those ST-26 engineer tanks only 12 were in good order, the others required repair.
Kolomiets (2007), pp. 91-94 (UST stands for usovershenstvovanniy saperniy tank or "improved engineer tank") - mod. 1936 was an improved version of the ST-26. Operation of the ST-26 engineer tanks had demonstrated their low reliability (frequent breaking of wire cables and bending of bridge supporting mounts), so the improved UST-26 was developed in 1936. The vehicle designers were the Red Army's Research Institute of Engineer Equipment (NIIIT RKKA) and the Gipstalmost Factory (engineers Vayson, Nemets and Markov). The UST-26 used a lever system of bridge laying with two levers and a hydraulic cylinder. The Factory No. 174 in co-operation with the Podolsk Machine Factory assembled two UST-26 in 1936. Trials performed in March 1936 showed the UST-26 was an improvement on the series-produced ST-26 (for example, the bridge raise operation did not require crew exit). Nevertheless, the UST-26 had its own disadvantages.
Remotely controlled tanks
TT-26 — Teletank
Self-propelled guns
SU-1 — Self-propelled gun armed with 76.2 mm regimental gun mod. 1927. The single fully armoured vehicle was built and tested in 1931. AT-1 — Artillery tank (tank of artillery support) armed with 76.2 mm PS-3 or L-7 tank gun. Two fully armoured vehicles were built and tested in 1935, 10 AT-1 artillery tanks were planned to be built in 1936 but were cancelled (Izhora Works produced 8 armoured hulls for the program). SU-5-1 — Self-propelled gun armed with the 76 mm divisional gun M1902/30 (open-top type, the single vehicle was built in 1934). SU-5-2 — Self-propelled gun armed with 122 mm howitzer M1910/30 (open-top type; a single vehicle was built in 1934 and a further 30 vehicles in 1936). SU-5-3 — Self-propelled gun armed with 152.4 mm divisional mortar mod. 1931 (open-top type, a single vehicle was built in 1934). SU-6 — Self-propelled gun armed with 76.2 mm 3K anti-aircraft gun (open-top type, a single vehicle was built in 1935 and 4 more vehicles armed with 37 mm anti-aircraft automatic gun were planned to be produced in 1936). SU-T-26 (SU-26, later SU-76P) — Self-propelled gun of an open-top design armed with a 37 mm gun or a 76.2mm regimental gun mod. 1927. The Factory of Hoisting-and-Conveying Machinery named after S.M. Kirov (in Leningrad) built 14 vehicles in 1941: probably 2 with a 37 mm gun and 12 with a 76 mm gun.
Armoured transport vehicles
TR-4 — Armoured personnel carrier TR-26 — Armoured personnel carrier TR4-1 — Ammunition transportation vehicle TB-26 — Ammunition transportation vehicle T-26Ts — Fuel transportation vehicle TTs-26 — Fuel transportation vehicle
Reconnaissance vehicles
Kolomiets (2007), pp. 120-121 (TN stands for tank nablyudeniya or "observation tank")