T-26
The T-26 tank was a Soviet light tank used during many conflicts of the Interwar period and in World War II. It was a development of the British Vickers 6-Ton tank and was one of the most successful tank designs of the 1930s until its light armour became vulnerable to newer anti-tank guns. It was produced in greater numbers than any other tank of the period, with more than 11,000 units manufactured. During the 1930s, the USSR developed 53 variants of the T-26, including flame-throwing tanks, combat engineer vehicles, remotely controlled tanks, self-propelled guns, artillery  tractors, and armoured carriers. Twenty-three of these were series-produced, others were experimental models. The T-26 and BT were the main tanks of the Red Army's armoured forces during the interwar period. The T-26 was the most important tank of the Spanish Civil War and played a significant role during the Battle of Lake Khasan in 1938, as well as in the Winter War in 1939–40. Though nearly obsolete by the beginning of World War II, the T-26 was the most numerous tank in the Red Army's armoured force during the German invasion of the Soviet Union  in June 1941. The T-26 fought the Germans and their allies during the Battle of Moscow in 1941–42, the Battle of Stalingrad and the Battle of the Caucasus in 1942–1943; some tank units of the Leningrad Front used their T-26s until 1944. Soviet T-26 light tanks last saw use in August 1945, during the defeat of the Japanese Kwantung Army in Manchuria. The T-26 was exported and used extensively by Spain, China and Turkey. Captured T-26s were used by the Finnish, German, Romanian and Hungarian armies. The tank was reliable and simple to maintain, and its design was continually modernised  between 1931 and 1941. No new models of the T-26 were developed after 1940. British origin. The T-26 (along with the Polish 7TP) was a Soviet development of the British Vickers 6-Ton (Vickers Mk.E variant) tank, which was designed by the Vickers-Armstrongs company in 1928–29. The simple and easy-to-maintain Vickers 6-Ton was intended for export to less technically advanced countries: the Soviet Union, Poland, Brazil, Argentina, Japan, Thailand, China, and many others. Vickers advertised the tank in military publications, and both the Soviet Union and Poland expressed interest in the Vickers design. In early  1930, the Soviet buying committee, under the direction of Semyon Ginzburg, arrived in Great Britain to select tanks, tractors, and cars for use in the Red Army. The Vickers 6-Ton was among four tank models selected by Soviet representatives during their visit to Vickers-Armstrongs. Under the contract signed on 28 May 1930, the company delivered to the USSR 15 twin-turreted Vickers Mk.E (Type A, armed with two .303 in (7.71 mm) water-cooled Vickers machine guns) tanks together with full technical documentation to enable series production of the tank in the USSR. The ability of the  two turrets of the Type A to turn independently made it possible to fire to both the left and right at once, which was considered advantageous for breakthroughs of field entrenchments. Several Soviet engineers participated in assembly of the tanks at the Vickers factory in 1930. The first four Vickers 6-Ton tanks arrived in the USSR at the end of 1930. The last tanks arrived in 1932, when series production of the T-26 was already in progress. The British tanks were sent to Soviet factories for study in preparation for series production and to military educational institutions and training  units. Later, some tanks were given to military supply depots and proving grounds. The Vickers-built 6-Ton tanks were called V-26 in the USSR. Three British tanks were tested for cross-country ability at the small proving ground near Moscow on Poklonnaya Hill in January 1931. Kliment Voroshilov ordered the creation of the "Special Commission for the Red Army (RKKA) new tanks" under the direction of S. Ginzburg to define the tank type suitable for the Red Army. The T-19 8-ton light infantry tank, developed by S. Ginzburg under that programme at the "Bolshevik" Plant in Leningrad, was  a competitor to the British Vickers 6-Ton. The first prototype of the complex and expensive T-19 was finished in August 1931. Because both tanks had advantages and disadvantages, S. Ginzburg suggested developing a more powerful, hybrid tank (the so-called "improved" T-19) with the hull, home-developed engine and armament from the native T-19, and the transmission and chassis from the British Vickers 6-Ton. On 26 January 1931, I. Khalepsky, Head of the Department of Mechanisation and Motorisation of the RKKA, wrote a letter to S. Ginzburg with information obtained via the intelligence service that the Polish government  had decided to purchase Vickers 6-Ton light infantry tanks as well as Christie "M1931" cavalry tanks and to mass-produce them with the assistance of both the British and French. Because Poland was then considered, in Soviet military doctrine, to be the USSR's main enemy, the Soviet Revolutionary Military Council decided to pass the foreign tanks into Red Army service, starting their production immediately without waiting for the completion of development works, in order to counter possible aggression. At that time, the RKKA had only several dozen outdated Mark V heavy tanks and Medium Mk.A and Renault  FT tanks, captured during the Russian Civil War, together with various armoured cars and obsolescent domestic MS-1 (T-18) light infantry tanks. On 13 February 1931, the Vickers 6-Ton light infantry tank, under the designator T-26, officially entered service in the Red Army as the "main tank for close support of combined arms units and tank units of High Command Reserve". One of the Vickers 6-Ton tanks (equipped with Soviet-made turrets for the pilot batch of T-26 tanks) was tested for gunfire resistance in August 1931. The hull was subjected to rifle and Maxim machine gun fire with  the use of normal and armour-piercing bullets at a range of . It was found that the armour withstood gunfire with minimal damage (only some rivets were damaged). Chemical analysis showed that the front armour plates were made from high-quality cemented armour ("S.t.a Plat" according to Vickers-Armstrongs classification), whereas the homogenous roof and bottom armour plates were made from mediocre steel. Even so, the British armour was better than armour produced by Izhora Factory for the first T-26s because of a shortage of modern metallurgical equipment in the USSR at that time. At the same time, the Faculty  of Mechanisation and Motorisation of the Military Technical Academy named after F.E. Dzerzhinsky developed two tank models (TMM-1 and TMM-2) based on the Vickers 6-Ton tank design but with an American Hercules six-cylinder water-cooled engine, improved front armour (to 15–20 mm), and a driver's position on the left side. TMM stands for "tank maloy moshchnosti" or "tank of low power". The TMM-1 was equipped with transmission details from the native and a ball mount for the DT tank machine gun in front of the hull, whereas the TMM-2 was equipped with an improved gearbox, a clutchless  steering device and a 37 mm Hotchkiss gun in the right turret. Representatives from the main Soviet tank manufacturers together with officials from the RKKA Mobilization Department considered the Hercules engine to be too difficult to produce, and the engine tended to overheat inside the engine compartment. Tests of TMM-1 and TMM-2 prototypes performed in the beginning of 1932 demonstrated no advantage over the Vickers 6-Ton and the T-26 (the TMM-2's maneuverability was found to be even worse). Design. The Soviets did not simply replicate the Vickers 6-Ton. However, like its British counterpart, the T-26 mod. 1931  had a twin-turreted configuration and was designed to carry two machine guns, mounting one in each turret. A major difference was that the Soviet T-26 mod. 1931 had higher turrets (with an observation slit) than the British 6-Ton. Soviet turrets had a round firing port for the Degtyarev light machine gun, as opposed to the rectangular ports used by the original British design for the Vickers machine gun. The front part of the hull was also slightly modified. Hulls of twin-turreted T-26s were assembled using armoured plates riveted to a frame from metal angles. Some tanks, produced  in 1931, had sealing zinc shims at the hull bottom between armoured plates for fording water obstacles. After problems with rain entering the engine compartment, a special cover was installed over an air outlet window after March 1932. Some T-26s produced at the end of 1932–1933 had a riveted and welded hull. The T-26 mod. 1931 had two cylindrical turrets mounted on ball bearings; each turret turned independently through 240°. Both turrets could provide common fire in front and rear arcs of fire (100° each). The disadvantage of such a configuration was that not all of the tank 's firepower could be used at once on the same side. Four turret modifications existed, and they were mounted on tanks in different combinations (for instance, a tank with a riveted hull could have riveted and welded turrets). The hull and turrets of the T-26 mod. 1931 had a maximum armour thickness of 13–15 mm (until 1938, see below), which was sufficient to withstand light machine gun fire. Many twin-turreted tanks of the first series had 10 mm armour plates of low quality, which could be penetrated by 7.62 mm armour-piercing bullets from In 1933, the Soviets unveiled  the T-26 mod. 1933. This model, which had a new single cylindrical turret carrying one 45-mm cannon L46 (length in calibre, which meant quite high initial velocity, over 700–800 m/s depending on ammunition) and one 7.62 mm machine gun, became the most common T-26 variant. The 45 mm 20K tank gun was based on the Soviet 45 mm anti-tank gun M1932 (19-K) and it was one of the most powerful anti-tank guns of its time. The T-26 could carry up to three secondary DT 7.62 mm machine guns in coaxial, rear, and anti-aircraft  mounts. This increased firepower was intended to aid crews in defeating dedicated anti-tank teams, as the original machine gun armament had been found insufficient. The turret rear ball mounting for the additional DT tank machine gun was installed on the T-26 tanks from the end of 1935 until 1939. The T-26 Model 1933 carried 122 rounds of 45 mm ammunition, firing armour-piercing 45 mm rounds with a muzzle velocity of , or lower-velocity high-explosive munitions. Tanks intended for company commanders were equipped with a radio set and a hand-rail radio antenna on the turret (so called  radio tanks). Later the hand-rail antenna was replaced with a whip antenna, because experience in the Spanish Civil War and Battle of Lake Khasan showed that the hand-rail antenna drew fire onto commander tanks. The tank was powered by a T-26 flat row 4-cylinder air-cooled petrol engine, which was a complete Soviet copy of the Armstrong Siddeley engine used in the Vickers 6-Ton. The engine was located in the rear part of the hull. Early Soviet-made tank engines were of bad quality but they became better beginning in 1934. The GAZ T-26 (a copy  of the Armstrong Siddeley Puma) engine did not have an over-speed limiter, which often resulted in overheating and engine valve breakage, especially in summer. A fuel tank for and an oil box for were placed alongside the engine. The engine required top-grade petrol; the use of second-rate petrol could cause damage to the valve units because of engine detonation. From mid-1932, a more capacious fuel tank — instead of — and a simplified oil box were introduced. An engine cooling fan was mounted over the engine in a special shroud. From early 1932, the exhaust silencer was affixed by  three clamps instead of two. The transmission of the T-26 consisted of single-disc main dry clutch connected to a gearbox, with five gears, in the front part of the vehicle by drive shaft passing through the vehicle. Steering was through steering clutches and band brakes. The gear change lever was mounted directly on the gearbox. Suspension (for each side) consisted of two bogies, four rubber-covered return rollers, a track driving wheel and a track idler. Each bogie consisted of a cast box with four twin rubber-covered road wheels connected by balancing levers and two one-quarter elliptic  leaf springs. The cast track driving wheel with removable sprocket ring was located in front, and the track idler with a crank lever tightener was located at the rear of the vehicle. The track was made from chrome-nickel steel wide and consisted of 108–109 links. The T-26 mod. 1931 did not have a radio set. The tank commander communicated with the driver by speaking tube, which was replaced with a signalling lamp in 1932. The T-26 was equipped with a fire extinguisher, a kit of spare parts tools and accessories (including a tank jack), canvas stowage, and a tow  chain fixed on the rear of the hull. The T-26 could cross -high vertical obstacles and -wide trenches, ford -deep water, cut -thick trees, and climb 40° gradients. Needless to say, it was easy to drive. Beginning in 1937, there was an effort to equip many tanks with a second machine gun in the rear of the turret and an anti-aircraft machine gun on top of it, as well as the addition of two searchlights above the gun for night gunnery, a new VKU-3 command system, and a TPU-3 intercom. Some tanks had a vertically stabilised TOP-1 gun  telescopic sight. Ammunition stowage for the main gun was increased from 122 rounds to 147. In 1938, the cylindrical turret was replaced with a conical turret, with the same 45 mm model 1934 gun. Some T-26s mod. 1938/1939, equipped with radio set, had a PTK commander's panoramic sight. In 1938, the T-26 was upgraded to the model 1938 version, which had a new conical turret with better anti-bullet resistance but the same welded hull as the T-26 mod. 1933 produced in 1935–1936. This proved insufficient in the Battle of Lake Khasan in 1938, so the tank was upgraded  once more in February 1939 to have an underturret box with sloped (23°) 20 mm side armoured plates. The turret featured an increase to 20 mm at 18 degrees sloping. This time it was designated T-26-1 (known as the T-26 mod. 1939 in modern sources). There were subsequent attempts to thicken the front plate, but T-26 production soon ended in favour of other designs, such as the T-34. Series production. The beginning. In 1931, the only Soviet factory suitable for T-26 production was the "Bolshevik" Factory in Leningrad, which had had experience of manufacturing the MS-1 (T-18) light  tanks since 1927. It was also planned to use the Stalingrad Tractor Factory, which was under construction at that time. But the production of the T-26 proved to be much more complicated than the semi-handicraft assembly of the MS-1, so the planned production of 500 T-26s in 1931 proved to be impossible. The "Bolshevik" Factory needed to convert all tank drawings from imperial units into metric, in order to develop a production technology, special tools, and equipment. The first 10 T-26s were assembled in July 1931 – they were identical to British Vickers 6-Ton tanks except for their armament . Soviet tanks were armed with the 37 mm Hotchkiss (PS-1) gun in the right turret and the 7.62 mm DT tank machine gun in the left turret. These T-26s from the development batch were of low quality and made from mild steel, but it was an important test of the new tank production technology. The series production of the T-26, equipped with new higher turrets with observation window, began in August 1931. Such turrets proved to be more suitable for mass production. The production of the T-26 encountered many problems: a lot of armoured hulls and turrets supplied by the  Izhora Factory were of low quality (with cracks) and were 10 mm thick instead of the planned 13 mm. Poor production standards were the reason behind the frequent failures of tank engines, gear boxes, springs in suspension, tracks and rubber-covered road wheels of early T-26s. Thirty-five of the 100 T-26s produced by the "Bolshevik" Factory in 1931 had hulls and turrets made from mild steel. Later, it was planned to replace these hulls with ones built of armour plate as well as to mount engines of better quality. The business plan for 1932 called for 3,000 T-26s. For  this, the tank workshop of the "Bolshevik" Factory was reorganised into the Factory No. 174 named after K.E. Voroshilov in February 1932. The director of the tank factory became K. Sirken and the chief engineer was S. Ginzburg. The problems with organizing the complicated new technological processes, poor production planning of parts suppliers, a great shortage of qualified engineers and technicians as well as of necessary equipment still resulted in many of the tanks being flawed, and they were not accepted by army representatives. On 26 October 1932, the Trust of Special Machine Industry, consisting of four factories, was established  to solve the problem of tank production in the USSR. The planned production of T-26s for 1932 was decreased significantly and special attention was given to increasing the quality of the tanks. A production run of the new model single-turreted T-26 armed with the 45 mm gun was launched in mid-1933. Factory No. 174 also manufactured a few T-26s for military educational institutions. These were dissected tanks to demonstrate the relative position and function of tank components during tank crew training. Production in Stalingrad. The Stalingrad Tractor Factory (STZ) was considered as one of the factories for production of  the T-26 from 1932, but production in Stalingrad did not start until August 1933. This process went very slowly, with great difficulties because of delays with deliveries of machining equipment and press tools for the newly built factory. In 1936–1939 the Design Office of the STZ developed several experimental tanks (6 TK, 4 TG, STZ-25, STZ-35) based on the T-26 tank and the STZ-5 transport tractor. For instance, the STZ-25 (T-25) had the turret, rear part of the hull, engine and some transmission details from the T-26 mod. 1938, but the STZ-25 wheeled-tracked tank weighed and had 16–24 mm  sloped armour. Factory managers tried to promote tanks of their own design rather than producing T-26s. As a result, the STZ failed to organise the series production of the T-26, but this experience helped to bring the T-34 into production in Stalingrad in 1941. The T-26s produced by STZ had no visual differences from other T-26s, but Stalingrad tanks were less reliable and more expensive. Modernization and repair. Some early T-26 tanks were repaired in tank units or factories with the use of later production parts. This meant replacing the all-rubber road wheels (except the front wheels) and track  idlers with new strengthened ones. Armour was added for the headlight, the armour thickness of the driver's hatch lower door of the twin-turreted tanks was increased from 6 to 10 mm and armoured PT-1 or PTK observation devices were installed. A common hatch above the engine, oil tank, and fuel tank was mounted starting in May 1940. In 1940, 255 T-26s were modernised in this way and in the first half of 1941 another 85 tanks were improved. A central factory responsible for the T-26's repair and modernisation was the Factory of Carrying-and-Conveying Machines named  after S. Kirov in Leningrad, and Factory No. 105 named after L. Kaganovich in Khabarovsk from the beginning of the Great Patriotic War until 1945. Production in 1941. Factory No. 174 produced its last T-26 tanks in February 1941. After that, the factory began retooling to produce the new and much more complex T-50 light tank. This work was slowed by delays in the delivery of new equipment and series production of the T-50 did not begin on schedule (planned for 1 June 1941). As a result, factory management decided to resume the production of the T-26, using T-26 hulls , turrets, and other parts already in stock. About 47 T-26 tanks were assembled and 77 were repaired in July–August 1941 before the factory was relocated from Leningrad to Chelyabinsk in the end of August 1941, and then to Chkalov in September 1941. Factory No. 174 produced engines and spare parts for the T-26, installed additional armour plates on some T-26s, replaced flame-throwers with 45 mm tank guns in turrets of 130 KhT-133 flame-throwing tanks, repaired tanks in army units (846 T-26s since the beginning of 1941) and mounted about 75 turrets from the T-26 and the T-50  as bunkers for the defence of Leningrad. Combat history. The T-26 entered active service for the Red Army (RKKA) in 1932; it was used in many conflicts of the 1930s as well as during World War II. The T-26 together with the BT was the main tank of the RKKA armoured forces during the interwar period. In the 1930s, T-26 light tanks were delivered to Spain (281 mod. 1933), China (82) and Turkey (60 mod. 1933 and 4 mod. 1931). The T-26 first saw action in the Spanish Civil War. T-26s were used in almost all Spanish Civil War military  operations against the Nationalists from 1936 to 1939 and demonstrated superiority over the German Panzer I light tanks and the Italian CV-33 tankettes, both of which were armed only with machine guns. During the battle of Guadalajara, T-26s outclassed the Italian tankettes, inspiring the design of the first Italian medium tank, the Fiat M13/40. During the war, Nationalist forces would attack the tanks with petrol bombs, the first time such weapons were used in war. They were used in the Second Sino-Japanese War by the Chinese from 1938 to 1944, especially in the Battle of Kunlun Pass. The next  military operation the T-26 light tank participated in was the Soviet-Japanese border conflict, commencing with the Battle of Lake Khasan, in July 1938. The 2nd Mechanised Brigade together with the 32nd and the 40th Independent Tank Battalions had 257 T-26s, from which 76 tanks were damaged and 9 burnt towards the end of battle action. A small number of T-26 tanks, as well as some flame-throwing tanks based on the T-26 chassis, participated in the Battle of Khalkhin Gol against Japanese forces in 1939. The T-26 was vulnerable to Japanese tank-killing teams armed with Molotov cocktails; poor  quality welds left gaps in the armour plate, and flaming petrol easily seeped into the fighting compartment and engine compartment. The 37 mm gun on the Japanese Type 95 light tank, despite its mediocre performance, was also effective against the T-26. Portions of the armour plating on earlier models of the T-26 used riveted construction and were very vulnerable to both types of attacks. The use of riveted armour on some older T-26 models led to "spalling", when the impact of enemy shells, even if they failed to disable the tank or kill the crew on their own, caused the  rivets to break off and become projectiles inside the tank. On the eve of World War II, T-26s served mainly in separate light tank brigades (each brigade had 256–267 T-26s) and in separate tank battalions of the rifle divisions (one company of T-26s consisted of 10–15 tanks). These were the type of tank units that participated in the Soviet invasion of Poland in September 1939 and in the Winter War from December 1939 – March 1940. The Winter War proved that the T-26 was obsolete and its design reserve was totally depleted. Finnish 37 mm antitank guns and even 20 mm  antitank rifles easily penetrated the T-26's thin anti-bullet armour and tank units equipped with the T-26 suffered significant losses during the breakthrough of the Mannerheim Line, in which the flame-throwing tanks based on the T-26 chassis played a significant role. By mid-1941, most of the Red Army's vast numbers of tanks were suffering from serious wear and tear. Poor quality roads, the vulnerabilities of track design in the early 1930s and inadequate maintenance, recovery and repair services all took their toll. In some of the front line armoured units, up to half of the T-26, T-28  and BT tanks had major drive train components (engine, drive train or suspension) that were broken down or worn out and these disabled tanks were parked and cannibalised for spare parts to keep the rest running. Tanks damaged during the 1939 Winter War with Finland were also cannibalised for parts. On 1 June 1941, the Red Army had 10,268 T-26 light tanks of all models on their inventories, including armoured combat vehicles based on the T-26 chassis. T-26s composed the majority of the fighting vehicles in the Soviet mechanised corps of the border military districts. For instance, the Western Special  Military District had 1,136 T-26 tanks on 22 June 1941 (52 percent of all tanks in the district). The T-26 (mod. 1938/39, especially) could withstand most German tanks in 1941 but were inferior to the Panzer III and Panzer IV participating in Operation Barbarossa in June 1941 and all of the Red Army's tank models suffered severe losses due to the air supremacy of the German "Luftwaffe". The majority of the Red Army's T-26s were lost in the first months of the German-Soviet War, mainly to enemy artillery and air attacks. Many tanks broke down for technical  reasons and lack of spare parts. As the war progressed and Germany's lighter tanks were replaced by the Panzer III, Panzer IV and heavier tanks, such as the Panther, the T-26 was gradually replaced through attrition by the vastly superior T-34. The remaining T-26s participated in battles with the Germans and their allies during the Battle of Moscow from 1941 to 1942, the Battle of Stalingrad and the Battle of the Caucasus from 1942 to 1943. Some tank units of the Leningrad Front used their T-26 tanks until 1944. The defeat of the Japanese Kwantung Army in Manchuria in  August 1945 was the last military operation in which Soviet T-26s were used. The Finnish Army used captured T-26s of different models during the Continuation War and some tanks served in Finland for various non-combat purposes until 1961. Captured T-26s were also used by the German, Romanian and Hungarian armies. The Romanian-captured vehicles saw some modifications (see below). Variants. Twin-turreted tanks. As the series production of the PS-2 gun was delayed, the Main Artillery Agency of the RKKA gave preference to a new gun. It was developed by the Artillery Design Office of the "Bolshevik" Factory, constructed  from parts taken from the previously purchased German 37 mm anti-tank gun developed by Rheinmetall and the PS-2 gun. This system was successfully tested and the Artillery Factory No. 8 named after M. Kalinin started its series production under the designator B-3 (5K). The B-3 gun had less recoil and a smaller breech compared to the PS-2, so it could be easily mounted in the normal machine gun turret of the T-26. The first twin-turreted T-26 was armed with a B-3 gun in the right turret in late 1931. Unfortunately, series production of the B-3 gun proceeded  slowly due to poor production standards (none of 225 guns produced in 1931 were accepted by army representatives; it took until 1933 to complete the original order for 300 guns placed in August 1931). Completed B-3 guns were mounted on BT-2 light tanks after mid-1932. This meant that twin-turreted T-26 tanks continued to be equipped with old 37 mm Hotchkiss (PS-1) guns. As production of the PS-1 gun had ended, some guns were taken from military supply depots and scrapped MS-1(T-18) tanks. The initial plan was to arm every fifth T-26 with the 37 mm gun in the right  turret, but the final proportion was somewhat higher. About 450 twin-turreted T-26 mod. 1931 tanks mounting the 37 mm gun in the right turret were produced in 1931–1933 (including only 20–30 tanks with the B-3 gun). There were 392 T-26 mod. 1931 tanks with gun plus machine gun armament in the Red Army on 1 April 1933. One twin-turreted T-26 was given to the Research Institute of Communication in March 1932 to develop special tank communication devices. The plan was to equip each tank with a keyphone, while a platoon commander's tank would be equipped with a  telephone switch for 6 subscribers (four for the tanks in the platoon, one for communication with infantry and one for contacting headquarters). A special terminal block was mounted on the rear of the tank so that communication wires could be connected. The work remained experimental. Single-turreted tanks. The T-26 mod. 1939 with appliqué armour weighed , which caused an overload of the chassis, transmission, and engine of the light tank. Drivers were advised to use low gears only. During the Great Patriotic War, a mounting of 15–40 mm appliqué armour on about a hundred different T-26s was performed by local  factories in Leningrad in 1941–1942, during the Siege of Odessa (1941), the Battle for Moscow and the Siege of Sevastopol (1941–1942). A cutting of armoured plates was more rough than developed during the Winter War; the majority of these modified tanks did not have a moving armoured gun mask as seen in Factory No. 174's original design, and some tanks had front appliqué armour only. Artillery tanks. It was found that the A-43 turret was very tight for two crewmembers; it had insufficient observation field; there was no turret ventilation, which made continuous gunfire difficult; and it was hard  to rotate the turret manually. At the beginning of 1933, a new 76 mm KT tank gun mod. 1927/32 with reduced (from 900 mm to 500 mm) recoil length was installed into the A-43 turret. The turret was still a very tight place for crew members. The ammunition stowage for 54 rounds was unsuccessful, and the military refused the A-43 turret. The T-26-4 with the KT tank gun passed tests successfully and five vehicles were built in 1933–1934 as pilot batch. Initially it was planned to arm three of these T-26-4 with the 76.2 mm KT tank gun  mod. 1927/32 and the other two tanks with the 76.2 mm PS-3 tank gun. The PS-3 tank gun was developed at the Experimental Engineering-Mechanical Department (OKMO) of the Factory No. 174 by engineer P. Syachentov. The PS-3 had better specifications in comparison with the series-produced KT tank gun and also had several technical innovations (foot firing switch, original training gear, travelling position fixing, binocular optical sight). The T-26-4 armed with the PS-3 tank gun was tested in October 1933 but it was found that the PS-3 was too powerful for the T-26 light tank—turret's race  ring and hull roof were deformed during gun fire, and the suspension springs were damaged. It was decided to arm the T-26-4 with the 76.2 mm KT tank gun only. All five experimental T-26-4 artillery tanks were tested during military exercises near Leningrad in September 1934 before scheduled series production of 50 such vehicles in 1935. But on 19 September 1934 an incident with a T-26-4 took place: a blow-back because of shell case destruction during gun fire. Despite the fact that this defect was unrelated to turret design, the military representatives cancelled the order to  produce the T-26-4. Also the work to design turretless AT-1 artillery tanks armed with the powerful 76.2 mm PS-3 tank gun started at that time. The T-26-4's turret construction was the design used in the series-produced BT-7A artillery tank. In 1939, the Armoured Directorate of the Red Army (ABTU RKKA) ordered the development of a new conical turret for the T-26 similar to the BT-7's turret and to arm it with the 76.2 mm L-10 tank gun. Engineers of the Factory No. 174 felt it was impossible to implement this project because it would lead  to a significant overload of T-26's chassis. Armoured combat vehicles. A large variety of different armoured combat vehicles were developed on the T-26 chassis in the 1930s. Among them were KhT-26, KhT-130 and KhT-133 flame-throwing (chemical) tanks (552, 401 and 269 vehicles were produced, respectively); T-26T artillery tractors (197 were produced); TT-26 and TU-26 remotely controlled tanks (162 teletanks of all models were produced); ST-26 bridge-laying tanks (71 were produced); SU-5 self-propelled guns (33 were produced); experimental armoured cargo/personnel carriers, reconnaissance vehicles, and many others. The majority of these vehicles 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. Various vehicle-mounted equipment was developed for the T-26, including mine-clearing attachments, inflatable pontoons and a snorkel system for fording water obstacles, devices for overcoming obstacles and many others. T-26 light tanks were also modified into different armoured combat vehicles in the field during wartime. Survivors. There are about 45 T-26 tanks of various models preserved in different museums and military schools (mainly  Russian, Spanish, Turkish and Finnish). The most notable of them are: