Probably something like Object 279
This unusual tank was designed in 1959 to fight on nuclear battlefields that the designers thought may exist in the future. Thankfully they didn't.
Key features that make it able to (it is claimed) survive a nuclear blast are:
- Heavy weight: at 60 tonnes it was about 20% heavier than many of it's contemporaries, preventing it from being tossed around easily.
- Low, aerodynamic profile: This tank doesn't have a curved profile for speed - it has it to deflect a blast wave up and over the top
- Extremely wide tracks: It's hard to push something around that has such a phenomenal level of surface traction. This also meant that this tank could navigate terrain that regular tanks would struggle with.
- Sealed interior and life support system: details are sketchy, but it is reported to have a degree of CBRN protection. This would likely include near airtight seals, and a comprehensive air treatment and filtration system.
In terms of armament, although the 130mm gun was not designed to fire nuclear shells, some of the smallest nuclear artillery shells designed were as small as 127mm with sub 1kt yields. According to nukemap a 1kt yield should have a fireball of about 80m in radius, and heavy damage out to about 220m. It seems plausible that this tank could launch shells far enough (modern effective ranges for tank guns seem to be about 4Km, so even 4km) to not be caught in the worst of the blast.
