The T-34 was developed from the BT series of fast tanks and was intended to replace both the BT-5 and BT-7 tanks and the T-26 infantry tank in service. At its introduction, it was the tank with the best balanced attributes of firepower, mobility, protection and ruggedness, although initially its battlefield effectiveness suffered from the unsatisfactory ergonomic layout of its crew compartment, scarcity of radios, and poor tactical employment. The two-man turret-crew arrangement required the commander to aim and fire the gun, an arrangement common to most Soviet tanks of the day; this proved to be inferior to three-man (commander, gunner, and loader) turret crews of German Panzer III and Panzer IV tanks.
The design and construction of the tank were continuously refined during the war to enhance effectiveness and decrease costs, allowing steadily greater numbers of T-34s to be fielded. In early 1944, the improved T-34-85 was introduced, with a more powerful 85 mm gun and a three-man turret design. By the war's end in 1945, the versatile and cost-effective T-34 had replaced many light and heavy tanks in service, and accounted for the majority of Soviet tank production. Its evolutionary development led directly to the T-54/55 series of tanks, built until 1981 and still operational as of 2010 and which itself led to the T-62, T-72 and T-90 tanks which, along with several Chinese tanks based on the T-55, form the backbone of many of the world's armies even today.
