No ground armor in Battletech is capable of resisting nukes unless we're talking about a heavily fortified bunker.
I specified kilotons, as in thousands of tons of TNT equivalent. Not nuclear, which is
expected to be
way the fuck above this bar. Battletech actually tends to hilariously lowball nuclear yields. A thousand pounds TNT isn't that far afield for heavy weaponry even today, for all it's heavy bomber territory.
Battletech's setting is one where the heaviest modern munitions before going nuclear are meant to be barely adequate stopgaps. And those munitions are in fact straddling the line of kilotons when you get into stuff like fuel-air bombs that would be
trivial for Mechs to use given the five-ton hatchets.
I'll largely ignore BTech's claimed yield on nukes because a half kiloton nuclear warhead's direct threat radius caps around 750 meters for
long term radiation poisoning, and the IRL 316 pound loaded namesake of that had its warhead readily repurposed to a half-kiloton back in the 80s with a 2.5 mile range on a goddamn recoilless rifle against the 3-ton rocket-artillery BTech version having half the range and the same yield. The absolute largest BTech nuke I can find is a 3 megaton design repurposed from a 90 ton conventional system, where the Russians managed a 50 megaton yield on a 27 ton warhead.
Those yields are a
joke for the way they're talked about. A 3 megaton device is only around 10 kilometers of causing bog-standard concrete buildings to collapse. With
any kind of meaningful advancement in infrastructure durability, as would be a
rather obviously high priority with the nukes being slung around, this drops
below 4 kilometers. You can gut
a particular factory, sure, but you're not taking out an industrial district with any kind of better-than-modern fortification without going quite a bit larger, let alone a city.
And the saturation needed to kill planets with radiation
on accident because you are
trying to conquer them? With 3 megaton warheads from a 90-ton system? Yeah, no, you need ground detonations with overall yields of gigatons for that to happen. This is
literally the "backyard bomb" phenomenon being done piecemeal, you'd be needing thousands of tons of munitions and get very obvious signs it's starting to happen long before being rendered truly unusable.
Like, we are literally talking about infantry ceasing to be useful because the acute fallout is killing them off nearly universally, and at that point it's a few decades to get to hazmats
unless you've gone full Backyard Bombing. A bother and murder on profit margins, but if there's any kind of actual strategic value you
need to be going for Tzar Bomb yields for this to end up happening. Horribly dirty
massive weapons that do in fact wipe a city out in one blast.
When we're talking about the low end, a half-kiloton's ability to damage hardened structures is synonymous with its 60m fireball. A 10 kiloton blast has 120 meters of 600 PSI overpressure
directly under the fireball, which is what's generally considered needed to render highways and airfields unusable, and 170 meters of that 200 PSI minimum for any damage to meaningful fortification.
Entirely sensible near-misses from personnel-safe launch distances by the (lack of) guidance standards of BTech are not remotely certain to be mission kills. At least by Nukemap. You'd actually have to proximity-fuse your tactical nukes to be sure about taking out Assault Mechs, given the forces the things put themselves under just
walking, let alone the wrestling, let alone what their guns are going to be doing.
*seeths in hatred of inverse inconsistency to Durasnow*
