The Soviet Объект 279 (Object 279) Super Heavy Tank. Produced in 1959 and only 1 built.
One of the unique tanks that were meant to be massed produced, but only one was made. The Object 279 was built for the Cold War and was meant to withstand a nuclear blast.
The tank weighed in at 66.14 tons (60 Metric Tons) and had four tracks. It's armor was 12.6 inches/319mm at it's thickest point. Height - 8 feet 8 Inches, Width - 11 feet 2 inches, Length - 22 feet 3 inches (36 feet 4 inches with gun forward).
Engine 1000hp diesel, operating range 190 miles, max speed 34 mph. Main gun 130mm M65 rifled barrel with semi-automatic loading system.
They only built one because the tank was too heavy per Nikita Khrushchev who was also leaning towards guided missile tanks that were lighter and easier to resupply.