By the end of 1940, when production of the T-34 started, there were already plans to improve the vehicle's reliability and operational capabilities by adopting more modern technology.
This design project was designated T-34M. It had enhanced armour protection, a three-man hexagonal turret, torsion bar suspension instead of Christie suspension, road wheels with internal shock absorption, increased fuel capacity, and more main gun ammunition (100 rounds instead of 77 in standard T-34). The bow machine gun and driver's hatch switched positions on the glacis plate. In addition to six smaller wheels, the suspension of the T-34M had four return rollers. The original model V-2 12-cylinder diesel engine developing 500 hp (373 kW) was replaced by a new 12-cylinder diesel engine which produced 600 horsepower (450 kW). It had a new 8-speed transmission system. It was the first tank design to feature transverse engine placement, which made it smaller than a standard T-34 and gave the crew more space.
The Zhdanov Metallurgical Factory manufactured five sets of armour plates for the hull of the T-34M and delivered them to Factory No. 183. However, early in 1941 work on the T-34M ceased as the production facilities were extremely busy with the mass production of the T-34. When the war with Nazi Germany broke out the only sensible solution was to gradually improve the existing design.
During the battles on the Eastern Front it became apparent that the Red Army needed a new medium tank. They requested that it should have better protection at a minimal increase of weight. In 1942 the T-43 tank design project began. It featured a new turret and shorter suspension which reduced the clearance between the roadwheels. However, it concentrated on increasing armour at a time when maintaining production and increasing firepower were more important. The T-43 was cancelled, but its new turret design was adapted to carry a larger 85 mm D-5T and later ZiS-S-53 gun in a new variant called the T-34-85. It marked the end of T-34 improvements as fitting 100 mm guns in T-34-100 prototypes proved unfeasible. (See T-34 variants article for details).
In the autumn of 1943 the design bureau of the Stalin Ural Tank Factory No. 183, located in Nizhny Tagil (in the Ural Mountains, where most of the Soviet tank industry had been evacuated after Operation Barbarossa in 1941), started working on a vehicle that would have improvement opportunities in the future, under a direct order from Joseph Stalin. The intention was to retain the high mobility of the T-34 and provide it with heavier armour protection against modern tank guns. In November 1943, the chief designer, A. A. Morozov, presented the overall design of the vehicle and a model of the tank, which received the designation T-44 (Ob'yekt 136). The first prototype was completed by January 1944 and two more were completed in February. The first two prototypes were armed with 85 mm D-5T guns and received the designation T-44-85, while the third prototype was armed with the 122 mm D-25-44T tank gun and received the designation T-44-122. The D-25-44T tank gun was very similar to the basic D-25 field gun, but differed in some minor details including fixed single-piece ammunition to increase the rate of fire and a double-baffle muzzle brake. What allowed fitting such powerful armament in a medium tank weighing 30 tonnes was the construction of the hull with an innovative placement of the engine. Unlike most tanks, in the T-44 the engine was placed perpendicular to the axis of the tank. The hull was designed without sponsons. It was also much wider which made the crew compartment bigger and allowed the turret to be placed over the center part of the vehicle. This reduced the overall length of the vehicle. The thickness of the armour was 75 mm on the front of the hull and 90 mm on the front of the turret. The side armour was 45 mm thick and could be reinforced by 30 mm thick additional armour plate. All three prototypes were powered by the V-2IS diesel engine which developed 500 hp (373 kW). This first generation of prototypes featured a raised cast driver's hatch with an opening vision flap as well as mounting bolts in a ring around the base of the gun tube.
Morozov's new medium tank design received a skeptical response. It was believed that putting a high-speed 12-cylinder engine with a working displacement of almost 40 liters perpendicular to the direction of travel would cause problems, including breaking the connecting rods. It was believed that decreasing the displacement of the engine compartment for the purpose of enlarging the fighting compartment was unnecessary and that moving the turret rearwards would limit the elevation angle of the main gun. However, it turned out that even though rotating the engine complicated the transmission by introducing an additional reduction gear - gear-train and fan drive, it also solved many problems. The cover of the engine and transmission compartment turned along with the radiator; this allowed easier access to the engine, transmission and batteries. The significant decrease in the length of the engine compartment allowed the turret to be moved rearwards, which in turn moved its rotation axis and the center of mass to the center of the hull, increased the accuracy of the main gun and decreased a chance that the turret could get stuck after getting hit in the turret ring with a projectile that ricocheted. The thickness of the frontal armor protection more than doubled without disturbing the center of mass or drastically increasing the weight of the tank. At the beginning of World War II the thickness of T-34 armor was considered enough. Improvements made to the T-34 during World War II included increasing the caliber of the gun (from 76.2 mm to 85 mm) and thickening the armor of the turret. No significant improvements were made to the hull. Increasing the size of the fighting compartment allowed the removal of floor ammunition stowage. The height of the tank was decreased by 300 mm, even though the turret remained almost the same. Removal of the conical pair in the transmission permitted fitting a more compact gear box and improved the control of the brakes and the steering clutch. Visibility from the driver's position was improved. The driver was protected from being splashed by water while the vehicle was fording. The new torsion bar suspension allowed easier crossing of rough ground.
T-44-122 prototype during comparative trials against captured German Panther
Second of the two first generation T-44-85 prototypes and T-44-122 prototype during comparative trials
The first trials of the T-44-122 prototype took place in February and March 1944, but were unsuccessful due to gun failure, and the gun was returned to the No. 9 factory for repair. In April and May 1944 the trials were resumed. Aside from standard trials, the T-44-122 was put in competitive trials against a captured German Panzerkampfwagen V Panther medium tank and the second of two first generation T-44-85 prototypes. The practical rate of fire was two to three rounds per minute due to the cramped turret and long, heavy ammunition. The vehicle had a very limited storage of only 24 rounds and this was considered insufficient for a medium tank. As a result, all further development of the T-44-122 prototype was cancelled.
Like the T-44-122 prototype, one of the two first-generation T-44-85 prototypes went through competitive trials against a captured German Panzerkampfwagen V Panther medium tank. The second of the two first-generation T-44-85 prototypes was put in competitive trials against the T-44-122 prototype. The second prototype uncovered additional faults in the design. By May 1944 two second-generation prototypes were being built. These featured the driver's position moved rearwards so that his hatch was partially on the hull roof. The driver's vision flap was reduced to a plain square flap with rounded lower corners, in line with the glacis plate. These prototypes had prominent collars at the base of the gun tube, without the mounting bolts which were present in the first generation prototypes. The two prototypes also have differences between each other. One prototype had a splashboard on the glacis plate while the other had a smooth uncluttered glacis plate. One of these prototypes passed trials at the NIBT proving grounds near Kubinka in June and July 1944. This prototype weighed 31.3 tonnes and was armed with an 85 mm ZiS-S-53 gun. The turret front armour thickness was increased to 115 mm. Hulls side armour thickness was increased to 75 mm.
The third generation prototype, which received the designation T-44A, was completed after the Morozov Design Bureau had moved back to Kharkiv in Ukraine. The hull upper front armour (glacis plate) thickness was increased to 90 mm and the turret front armour thickness was increased to 120 mm. Even though it was more heavily armoured, the weight went down to 30.7 tonnes. This vehicle had a new V-44 12-cylinder 4-stroke diesel engine of 520 hp (388 kW) at 1,800 rpm, which allowed the tank to travel at a speed of 60.5 km/h. This prototype had the splashboard on the glacis plate like one of the second generation T-44-85 prototypes. This prototype featured some other differences from the earlier prototypes, including the fact that drivers hatch was moved entirely to the roof of the hull and the vision flap was deleted from the design and replaced by a vision slot in the glacis plate. After trials conducted in August and September 1944 and after it received several upgrades (which increased the weight of the vehicle to 32 tonnes), the T-44A officially entered service with the Red Army on the 23 November 1944, but did not see combat during World War II.
T-44-100 and T-54
One of the two T-44-100 prototypes. Notice the 100 mm gun, 12.7 mm DShK anti-aircraft heavy machine gun mounted on the loader's hatch and 6 mm thick anti-HEAT sideskirts protecting the sides. This example does not have a splashboard on the glacis plate.
Even with its innovative technology and better armor protection, the T-44A still used an 85 mm ZiS-S-53 tank gun, the same as the one fitted on the T-34-85 medium tank. The army needed a new tank armed with a more powerful 100 mm gun. At the end of 1944 the designers had three types of 100 mm guns at their disposal which could considerably increase the firepower of the tank. These included the D-10 (which already proved itself in combat as it was used in SU-100 tank destroyer) as well as prototype ZiS-100 and LB-1 (LB stands for Lavrenty Beria). The T-44 tank armed with the 100 mm tank gun originally received the designation T-44B. Two projects were started, both based on the T-44A. The development of the first one started in October 1944 at the design bureau of the Stalin Ural Tank Factory No. 183, located in Nizhny Tagil. The designing stage was completed in December. The prototype was ready in February 1945. The trials conducted between March and April gave positive results and the vehicle entered service with the Red Army as T-54. The tank had almost the same hull and drive train as the T-44A. Differences included thickened front armour (120 mm on the upper section and 90 mm on the lower section) and a different hatch and vision slot for the driver. The turret had increased diameter to 1800 mm. There was thicker armour (180 mm on the front, between 90 mm and 150 mm on the sides and 30 mm on the roof). The armament included the 100 mm D-10TK tank gun as well as two 7.62 mm GWT machine guns. The tank was powered by a new V-54 12-cylinder 38.88 liter water-cooled diesel engine developing 520 hp (388 kW) at 2,000 rpm. The fuel capacity was increased (530 liters in the internal fuel tank and 165 liters in the external fuel tank). The external fuel tanks were connected to the fuel system. The rubber rollers on the roadwheels were widened. The weight was increased to 35.5 tonnes, which reduced the maximal road speed to 43.5 km/h. The maximal road operational range increased to 360 km. Because of positive results seen in trials, it was decided to modernize the tank before starting production (for more details about it see the T-54/55 article) as well as to put the new tank's turret onto two modified serial T-44A tanks. This was done in 1945 and the two prototype tanks received the designation T-44-100. One of the prototypes was armed with a D-10TK tank gun while the other one was armed with a LB-1 tank gun. Like the second generation T-44-85 prototypes, the two T-44-100 prototypes had differences between each other. One prototype had a splashboard on the glacis plate while the other did not. They both had the 12.7 mm DShK anti-aircraft heavy machine gun fitted to the loader's hatch, 6 mm thick anti-HEAT sideskirts protecting the sides and two cylindrical fuel tanks in the back which increased the fuel capacity to 1035 liters. These cylindrical fuel tanks were later used on Soviet main battle tanks as additional fuel tanks. Further development of the T-44 was canceled and all the attention was directed towards the development of a new T-54 main battle tank.