Soviet IS-7, the best tank in the world (for its time)

Tank featured roughly 350 mm of effective front armor, not even all Gen2 MBTs had that much armor.

Its 130 mm gun could deal with any other tank target it faced, while being frontally immune against it (for its time ofc). Unlike other soviet heavy tanks which had an awful reload time, IS-7 had a semi-autoloader which made reload time much faster.

Weight was some 68 tons, but top speed was still 60 km/h i.e. on par with Gen1 MBTs.

Despite all the advantages, IS-7 never entered service or production because it was too expensive. Only few prototypes were built.