Also known as T-28A, T-28 was multi-turreted medium tank (sometimes refereed as heavy tank) developed in the early 30'. In it's time, the design was advanced without a competition, but the Spanish Civil War and Winter War showed the armor protection was inadequate, and suspension was very weak.
T-28 Model 1934 was the first (and main) production version produced from 1932. It's characteristic trait is main turret with short 76mm gun and two machine gun turrets on the front. T-28 was good in it's time as infantry support, but even after modernizations in 1939-40, most of them were destroyed during German invasion. "TU" stands for "tank upravleniya", "command tank" as it is equipped with a hand-rail frame antenna.
NOTE: Addition of TU is my personal choice. Officially it was just T-28 with hand-rail frame antenna.