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In some senses, tacnuke is marked as slang, figuratively, US, colloquial. Watch for register when choosing this word.
noun
A tactical nuclear weapon.
Probably it would go as this: the Soviets attack with as little warning as possible in a holiday with a massive BC assault together with their mechanized wave. Maybe a tacnuke or two (or two dozens) are exchanged between WARPACT and NATO troops in Germany and Turkey (i'm thinking of the Thrace area). After 2-3 weeks either the Soviets reach the Rhine and ask for an armistice or the war stalemates and ask for an armistice.
verb
To use a tactical nuclear weapon on a target.
To destroy or erase completely.