The broadly-accepted tank doctrine of the pre-World War 2 period (mainly the 1930s) was to utilize two very distinct tank types when attempting to demolish an enemy's defenses. This thinking involved "fast tanks" designed around speed to be used to overwhelm the enemy while "infantry tanks" would be sent in to fight alongside advancing infantry forces. Infantry tanks ran contrary to the design of fast tanks in that they were to feature much heavier armor protection and larger-caliber main armament - making them slow but harder to stop. In 1937, Soviet tank engineers began work on the latter type through "Object 111" - or the "T-111" - at the Kirov Works, No.185 plant of Leningrad.
The new vehicle was a "light tank" by classification but intended for the infantry role nonetheless. It was to incorporate enough armor protection so as to withstand the power of 37mm shells fired at close-to-medium-ranges and 76.2mm shells fired out from over 1,000 meters. The tank was originally drawn up to showcase a combat weight of 20 tonnes or less. However, the work was considerably delayed when its lead engineer was detained during Stalin's "purges" - this left the T-111 in limbo until work progressed enough in April of 1938 to reveal a pilot (prototype) vehicle.
The resulting 32-tonne tank was of conventional arrangement: its crew numbered three (driver, commander and gunner) and the primary armament was contained in a fully-traversing turret. With the crew taking up their positions in the forward and middle sections of the hull, this left the engine to reside in the rear. Armor protection ranged from 20mm to 60mm at the critical facings, namely the front and sides, but this added weight came at a price. Dimensions included a running length of 5.26 meters with a beam of 3.1 meters and a height of 2.4 meters.
Power was from a single MT5-I 12-cylinder diesel-fueled engine outputting 300 horsepower and this was used to drive a modern track-and-wheel arrangement featuring six double-tired roadwheels to a hull side with the drive sprocket at front and the track idler at rear. Three track-return rollers were used to guide the slim track-links about the upper reaches of the hull sides. The vehicle could theoretically manage a road speed maximum of 30 kmh out to a range of 150 kilometers - but this only on prepared roads and not cross-country.
Primary armament was the proven 45mm 20K L/46 main gun and this was fitted at the forward face of the turret. Up to 3 x 7.62mm DT machine guns were carried to help defend the vehicle from infantry as well as assail infantry positions at range. One was installed in a coaxial mounting alongside the main gun at the front turret face while another was featured facing the rear of the tank at the rear turret wall (to protect the more vulnerable rear quadrant from infantry attack). A spotlight was affixed to the main gun near the mantlet.
The T-111 was ultimately evaluated through two completed pilot vehicles but the design was soon found to be heavy, cumbersome and lack the needed firepower to counter growing threats of the day. Because there was little that could be done to extract additional improvements from the existing design, the Object 111 program was abandoned in full before the end of the decade.