The Soviets were proud of their T-34 tanks. It changed the course of the war. So good, the Germans tried copying it then went for a different design utilizing the same sloped armor innovation with the Panther tank.
The next revolutionary tank for the Soviets was the T-64 tank. The 4 suffix made it clear. It incorporated a new advanced composite armor and featured the first autoloader.
Now the Russians think their Armata tank is a game changer, thus, the suffix of 4, T-14 Armata.
So capable, the T-64 tanks are still in service with the Ukrainian army...
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