Well if trident gets used then what comes next is irrelevant.

It's like planning for your house burning down V dying. If you're dead you don't really need to worry about the after.

So yes the military plans for everyone but global thermo nuclear war, because there's no point planning for that anyway.

I wouldn't say were planning for the next ww2. Look at the number of tanks we have. If anything were over optimised for helping the US fight insurgencies in the middle east at the expense of being able to fight a high intensity war.