The Apocalypse Troll — David Weber

USN vs UFOS

There he was in his sailboat in the middle of the Atlantic, all alone and loving it. Well, there was a US Navy carrier group on his southern horizon, but he was a Navy guy himself, so he didn't mind. Then came the UFOs, hurtling in from the Outer Black to overfly the carriers at Mach 17. Their impossible aerobatics were bad enough--but then they started shooting at each other. And at the Navy. With nukes. Little ones at first, but winding up with a 500 megatonner at 90 miles that fried every piece of electronics within line-of-sight.

Richard Aston thought he was just a ringside observer to these now over-the-horizon events. Until the crippled alien lifeboat came drifting down and homed in on his sailboat; suddenly he has his hands full of an unconscious, critically wounded and impossibly human alien warrior who also happens to be a gorgeous female.

That's when things got interesting.