Can't believe I hadn't brought this one up, I read it a long time ago. Like, when I was still running T2k and the USSR was a real thing. I read at least one of the stories in Pournelle's mil-sci-fi "There will be war" anthologies, and then this volume came out in 1989.
It's a collection of short stories in the Irish village of Barley Cross. Some catastrophe has happened-- left largely undefined-- and all the men in the world are no longer fertile. Except one, it seems, and he's a British Army sergeant who's deserted with his Chieftain. He rumbles into the village and the village council sets him up as Military Advisor, moves him into an old castle, and then they find out his, er, "superpower".
How far will they go to try to re-start the human species?
For T2k: Hardly a battle scene to be had, it's a lot more about what decisions people make under TEOTAWKI situations. There's no outside government or other institutions, marauders dispute the roads. It could easily be a solitaire game of T2k, just far from the nukes.
I think this and John Ringo's Kildar series are about half of why I'd like to run a "settling down" game in T2k someday.