Ragnarok by Patrick A. Vanner.
Humanity is locked in a war of survival with the Xan-Sskarn, an alien race that refuses to acknowledge the rights of "weaker" creatures to live. It is a war that will not end with a peace treaty, but only the complete subjugation of one species to the other. And right now, the alien side is winning.
The protagonist is Alex McLaughlin.
There's a description of the Loki fighters when Alan Lewis asks Tracy Clark about them:
"Have you ever heard of Lokis?"
"Yeah, we touched on them briefly at Intel school. Didn't go into too much depth, though. They're some kind of EW ship, right?"
"Sort of, though they are more than a space-based Electronic Warfare platform. Anyway, Loki pilots are always referred to as Dead Jokers."
Tracy watched Alan digest this information, waiting for the inevitable follow-up questions.
You can read the first chapter on the Baen web site (though that doesn't mention the Loki fighters).