Development and production
In 1939, the most numerous
Soviet tank models were the
T-26 infantry tank and the
BT series of fast tanks. The T-26 was slow-moving, designed to keep pace with infantry on the ground. The BT tanks were
cavalry tanks: fast-moving and light, designed for manoeuvre warfare. Both were Soviet developments of foreign designs from the early 1930s; the T-26 was based on the British
Vickers 6-Ton, and the BT tanks were based on a design from American engineer
J. Walter Christie.
BT-7, A-20, T-34 (model 1940), and T-34 (model 1941)
In 1937, the
Red Army had assigned engineer
Mikhail Koshkin to lead a new team to design a replacement for the BT tanks at the
Kharkiv Komintern Locomotive Plant (KhPZ). The
prototype tank, designated A-20, was specified with 20 mm (0.8 in) of
armour, a 45 mm (1.77 in) gun, and the new
Model V-2-34 engine, using less-flammable diesel fuel in a
V12 configuration designed by
Konstantin Chelpan. It also had an 8×6-wheel convertible drive similar to the BT tank's 8×2, which allowed it to run on wheels without
 This feature had greatly saved on maintenance and repair of the unreliable tank tracks of the early 1930s, and allowed tanks to exceed 85 kilometres per hour (53 mph) on roads, but gave no advantage in combat and its complexity made it difficult to maintain. By 1937–38, track design had improved and the designers considered it a waste of space, weight, and maintenance resources, despite the road speed advantage.
 The A-20 also incorporated previous research (BT-IS and BT-SW-2 projects) into
sloped armour: its all-round sloped armour plates were more likely to deflect rounds than perpendicular armour.
Battle of Lake Khasan in July 1938 and the
Battles of Khalkhin Gol in 1939, an undeclared border war with
Japan on the frontier with occupied
Manchuria, the Soviets deployed numerous tanks against the
Imperial Japanese Army (IJA). Although the IJA
Type 95 Ha-Go light tanks had
 the Red Army's T-26 and BT tanks used petrol engines which, while common in tank designs of the time, often burst into flames when hit by IJA tank-killer teams
Molotov cocktails. Poor quality welds in the Soviet armour plates left small gaps between them, and flaming petrol from the Molotov cocktails easily seeped into the fighting and engine compartment; portions of the armour plating that had been assembled with
rivets also proved to be vulnerable.
 The Soviet tanks were also easily destroyed by the Japanese Type 95 tank's 37 mm gunfire, despite the low velocity of that gun,
 or "at any other slightest provocation".
 The use of riveted armour led to a problem called "
spalling", whereby the impact of enemy shells, even if they failed to disable the tank or kill the crew on their own, would cause the rivets to break off and become projectiles inside the tank.
After these battles, Koshkin convinced Soviet leader
Joseph Stalin to let him develop a second prototype, a more heavily armed and armoured "universal tank" that reflected the lessons learned and could replace both the T-26 and the BT tanks. Koshkin named the second prototype A-32, after its 32 mm (1.3 in) of frontal armour. It had an L-10 76.2 mm (3 in) gun, and the same Model V-2-34 diesel.
 Both were tested in
field trials at
Kubinka in 1939, with the heavier A-32 proving to be as mobile as the A-20. A still heavier version of the A-32, with 45 mm (1.77 in) of front armour, wider tracks, and a newer L-11 76.2 mm gun, was approved for production as the T-34. Koshkin chose the name after the year 1934, when he began to formulate his ideas about the new tank, and to commemorate that year's decree expanding the armoured force and appointing
Sergo Ordzhonikidze to head tank production.
Valuable lessons from Lake Khasan and Khalkhin Gol regarding armour protection, mobility, quality welding, and main guns were incorporated into the new T-34 tank, which represented a substantial improvement over the BT and T-26 tanks in all four areas.
 Koshkin's team completed two prototype T-34s in January 1940. In April and May, they underwent a grueling 2,000-kilometre (1,200 mi) drive from
Moscow for a demonstration for the
Kremlin leaders, to the
Mannerheim Line in
Finland, and back to Kharkiv via
drivetrain shortcomings were identified and corrected.
Pre-production prototype A-34 with a complex single-piece hull front.
Political pressure came from conservative elements in the army to redirect resources into building the older T-26 and BT tanks, or to cancel T-34 production pending completion of the more advanced
T-34M design. This pressure was brought to bear by the developer of the
KV-1 tank which was in competition with the T-34.
Resistance from the military command and concerns about high production cost were finally overcome by anxieties about the poor performance of Soviet tanks in the
Winter War in Finland, and the effectiveness of German tanks during the
Battle of France. The first production T-34s were completed in September 1940, completely replacing the production of the T-26, the BT series, and the multi-turreted
T-28 medium tank at the KhPZ plant.
 Koshkin died of pneumonia (exacerbated by the drive from Kharkiv to Moscow) at the end of that month, and the T-34's drivetrain developer,
Alexander Morozov, was appointed Chief Designer.
The T-34 posed new challenges for Soviet industry. It had heavier armour than any medium tank produced to date, and there were problems with defective armour plates.
 Only company commanders' tanks could be fitted with radios (originally the 10-RT 26E radio set), due to their expense and short supply – the rest of the tank crews in each company signalled with flags.
 The L-11 gun did not live up to expectations, so the
Grabin Design Bureau at
Gorky Factory N.92 designed the superior
F-34 76.2 mm gun (see
Designations of Soviet artillery). No bureaucrat would approve production of the new gun, but Gorky and KhPZ started producing it anyway; official permission only came from the
State Defense Committee after troops praised the weapon's performance in combat against the Germans.
Production of this first T-34 series – the Model 1940 – totalled only about 400,
 before production was switched to the Model 1941, with the F-34 gun, 9-RS radio set (also installed on the
SU-100), and even thicker armour.
T-34 tanks headed to the front.
Subassemblies for the T-34 originated at several plants: Kharkiv Diesel Factory N.75 supplied the model V-2-34 engine, Leningrad
Kirovsky Factory (formerly the Putilov works) made the original L-11 gun, and the Dinamo Factory in Moscow produced electrical components. Tanks were initially built at KhPZ N.183, in early 1941 at the
Stalingrad Tractor Factory (STZ), and starting in July at
Krasnoye Sormovo Factory N.112 in
(June 1941 –
|KV and KV-85
Germany's surprise invasion of the Soviet Union on 22 June 1941 (
Operation Barbarossa), the
Wehrmacht's rapid advances forced the evacuation and relocation of Soviet tank factories eastwards of the
Ural Mountains, an undertaking of immense scale and haste that presented enormous logistic difficulties and was extremely punishing to the workers involved. Alexander Morozov personally supervised the evacuation of all skilled engineers and labourers, machinery and stock from KhPZ to re-establish the factory at the site of the
Dzerzhinsky Ural Railcar Factory in
Nizhny Tagil, renamed Stalin Ural Tank Factory N.183.
 The Kirovsky Factory, evacuated just weeks before the Germans surrounded Leningrad, moved with the Kharkiv Diesel Factory to the
Stalin Tractor Factory in
Chelyabinsk, soon to be nicknamed Tankograd ("Tank City"). The workers and machinery from Leningrad's Voroshilov Tank Factory N.174 were incorporated into the Ural Factory and the new Omsk Factory N.174. The
Ordzhonikidze Ural Heavy Machine Tool Works (UZTM) in
Sverdlovsk absorbed workers and machines from several small machine shops in the path of German forces.
While these factories were being rapidly moved, the industrial complex surrounding the
Dzerzhinsky Tractor Factory in Stalingrad continued to work double shifts throughout the period of withdrawal (September 1941 to September 1942) to make up for production lost, and produced 40% of all T-34s during the period.
 As the factory became surrounded by heavy fighting in the
Battle of Stalingrad in 1942, the situation there grew desperate: manufacturing innovations were necessitated by material shortages, and stories persist of unpainted T-34 tanks driven out of the factory directly to the battlefields around it.
 Stalingrad kept up production until September 1942.
Soviet designers were aware of design deficiencies in the tank, but most of the desired remedies would have slowed tank production and so were not implemented: the only changes allowed on the production lines through to 1944 were those to make production simpler and cheaper. New methods were developed for automated
hardening the armour plate, including innovations by Prof.
 The design of the 76.2 mm
F-34 gun Model 1941 was reduced from an initial 861 parts to 614.
 The initial narrow, cramped turrets, both the cast one and the one welded of rolled armour plates bent to shape, were since 1942 gradually replaced with the somewhat less cramped hexagonal one; as it was mostly cast with only a few, simple flat armour plates welded in (roof etc.), this turret was actually faster to produce. Limited
rubber supplies led to the adoption of all-steel, internally sprung road wheels, and a new clutch was added to an improved five-speed transmission and engine, improving reliability.
Polish T-34 Model 1943 in
, Poland. The model 1943's hexagonal turret distinguishes it from earlier models.
Over two years, the unit production cost of the T-34 was reduced from 269,500
rubles in 1941, to 193,000, and then to 135,000.
 Production time was cut in half by the end of 1942, even though most experienced factory workers had been sent to the battlefield and were replaced by a mixed workforce that included 50% women, 15% boys, and 15% invalids and old men. Originally "beautifully crafted machines with excellent exterior finish comparable or superior to those in Western Europe or America", later T-34s were much more roughly finished; however, this did not compromise mechanical reliability.
In 1943, T-34 production had reached an average of 1,300 per month; this was the equivalent of three full-strength
 By the end of 1945, over 57,300 T-34s had been built: 34,780 T-34 tanks in multiple variants with 76.2 mm guns in 1940–44, and another 22,609 of the revised T-34-85 model in 1944–45.
 The single largest producer was Factory N.183 (UTZ), building 28,952 T-34s and T-34-85s from 1941 to 1945. The second-largest was
Krasnoye Sormovo Factory N.112 in Gorky, with 12,604 in the same period.
At the start of the war, T-34s comprised about four percent of the Soviet tank arsenal, but by the end it made up at least 55% of tank production (based on figures from;
Zheltov 2001 lists even larger numbers).
Following the end of the war, a further 2,701 T-34s were built prior to the end of Soviet production. Under licence, production was restarted in
Poland (1951–55) and
Czechoslovakia (1951–58), where 1,380 and 3,185 T-34-85s were made, respectively, by 1956.
 Altogether, as many as 84,070 T-34s are thought to have been built, plus 13,170 self-propelled guns built on T-34 chassis.
 It was the most-produced tank of the Second World War, and the second most-produced tank of all time, after its successor, the