The Russian T-34 Battle Tank

It is not true that the T-34 — a great surprise for the German soldiers in World War II — arose out of the blue. There was simply a lack of reconnaissance.
The BT (Bystrochodya Tank = Fast Tank) 1-7 series, which originated in 1931, and the BT-IS (Ispitatelniy = Researcher) developed in 1936 featured from the start the Christie running gear with the big road wheels, which was later typical of the T-34 as well. Since the BT-7 they were equipped with robust Diesel engines, and the BT-IS was the first to have angled armor plate. All of them, including the two successor models, the A-20 and A-30, were still armed with a 4.5 cm tank gun and could travel on their road wheels even without tracks — hence the "Fast Tank" designation.