Soviet IS-2 Heavy Tank. It's gun (A-19 later D-25T 122 mm gun) was way too big, it had much too slow muzzle velocity and it used a separate shell and powder charge. Resulting in a lower rate of fire and reduced ammunition capacity, both serious disadvantages in tank-to-tank engagements. It was the large HE shell the gun fired which was its main asset, proving highly useful and destructive in the anti-personnel role and attacking German fortifications. What are your thoughts?