The need for a better weapon than the ZIS S-53 85mm gun on the T-34-85 became evident during the war. The most common ammunition type was the BR-365K AP-T. With an initial muzzle velocity of 792 meters per second, it could penetrate 102 millimeters of armor at 1,000 meters. This round was supplemented by the the BR-365P HVAP-T round, which had a tungsten carbide core. With an initial muzzle velocity of 1,030 meters per second, it had a penetration of 130 millimeters at 1,000 meters. The German Panther tank had turret front armor 110 millimeters thick and a glacis plate 80 millimeters thick (at 55 degrees). As a result of the armor layout, the Panther could not be easily penetrated using the standard BR-365K in a frontal engagement at 1,000 meters, and was only marginally vulnerable to the less common BR-365P ammunition.
The Soviet Union had been provided with a single example of the US Army M26 Pershing tank through Lend-Lease. This tank had thicker armor than the Panther: a glacis plate of 100 millimeters (at 46 degrees) and turret frontal armor of 114 millimeters. Both the Panther and M26 were considerably more vulnerable to attack by the 85mm gun from side angles of course. The Soviet Union was probably unfamiliar with armor details of the British Centurion tank.
Although the German Panther, American Pershing and British Centurion tanks were heavy tanks by Soviet standards, it had become evident to Soviet tank designers that these 45-ton tanks would become the medium tank class, of the post-war generation. The 85mm gun on the T-34-85 and T-44 tanks was still a viable weapon in the short-term, but there was clearly the need for an improved weapon in the long term to deal with improved derivatives of the M26 and Centurion.
Such a weapon was already available in the form of the 100mm D-10 rifled gun, developed by General F. Petrov's design bureau in Sverdlovsk at Artillery Plant Number 9. This weapon had originally been developed in 1944 to arm the SU-100 tank destroyer, based on the T-34 chassis. It had been considered for arming the IS-2 but rejected because, at the time, the ammunition was only beginning to enter large-scale production for the army. With the war over, however, the logistics concerns were no longer of paramount importance. The D-10 gun offered a substantial improvement in antiarmor performance. The BR-412 AP-T round had an initial muzzle velocity of 1,000 meters per second and an armor penetration of 185 millimeters at 1,000 meters. This was more than adequate to defeat any existing tank short of the rare German King Tiger heavy tank.
The Petrov D-10 100mm gun was already in production, along with the towed 100mm BS-3 antitank gun designed by the rival V. Grabin design bureau. For unknown reasons, a third gun was considered for the new tank gun, called the LB-1. The LB stood for Lavrentiy Beria, the head of the Soviet secret police, and reflected the fact that the gun was designed by one of the "special technical bureaus" organized of engineers imprisoned in the GULAG. It is possible that the team included captured German engineers.
The initial attempts were directed at mounting the D-10 and LB-1 in the T-44 tank. However, the engineers were skeptical of this effort because of the enormous size of the D-10's breech block and the relatively small space available inside the T-44 turret. A testbed of the T-34, armed with the 100mm gun as the T-34-100 had already been built. As a result, a parallel program called the Obiekt 137 was started using a new turret on the T-44 chassis to provide the added space.
In December 1944, Morozov's bureau had completed initial design work on Obiekt 137, also known as the B-40. The new turret was more thickly armored than the turret on the T-44, and indeed its frontal armor of 200 millimeters was as thick as that on the German King Tiger tank. The new turret was designed from the outset to carry the D-10 100mm gun. The new turret required hull extensions added on either side to increase the turret race diameter. The turret was significantly different than on subsequent models, with a conventional, wide mantlet, and prominent turret overhang both front and rear.
It was fitted with two SG-43 machine guns mounted in boxes on either fender for defense against infantry; curiously enough, the US Army also experimented with fender-mounted machine guns around this time to replace the separate machine gun station in the hull so typically found on wartime tanks. Other internal changes of the T-54 were the improved V-54 engine, and a planetary gear box to overcome problems on the T-44 powertrain.
The new T-54s were tested by tank units in the Byelorussian Military District. The trials were a fiasco with many faults discovered during operation, especially poor reliability. The situation was so serious that complaints were sent directly to the Politbureau. The plan had been to begin production in 1949, but instead, the assigned factories halted production while awaiting the modifications to be implemented. This order apparently affected only the three plants assigned to the T-54 program: Nizhni-Tagil, Omsk and Kharkov, as US Army intelligence concluded from tanks captured in Korea that production of the T-34-85 continued at Gorkiy's Krasnoye Sormovo plant through 1950.
On 20 May 1945, the final drawings of the vehicle were transferred to the Nizhni Tagil factory for prototype construction. Prototypes of this tank were completed in 1946, and it became known as the T-54 Model 1946. T-44 production was halted in 1946 in order to permit small-scale production of the T-54 Model 1946 for operational trials. In 1948, Morozov and his design bureau (including A.Kolesnikov, V. Matyukhin, P.Vasiliev and N.Kucherenko) received a state prize for its new tank design.
