ModernMilitary/fantasy/Transported to a fantasy world
Anime called GATE, something like that
The juxtaposition that comes with the modern military vs fantasy, does not lend itself to an easily told story. Any attempt that I've seen usually gets to 10-ish chapters before the author runs out of steam. There doesn't really exist any reference material to work from and thus the concept is hard to properly write and keep interesting without cliches.
It's already hard to power balance the two inherently different power systems and this is further exacerbated by the challenge of writing to the scope of military fiction. It isn't impossible to write this type of story, it's just very challenging and so far nothing has done it justice.
I hope I'm wrong and someone can name a book, but my own research has never born any fruit in this endeavour.
It's not exactly what you were looking for but it might scratch the same itch.
Not going to lie I still enjoyed it and it wasnt terribly long either.
Release that witch also has some of those themes and is a recommended read, if you can stand harem styled content that is.
There are a bunch I have read before but I wouldn't say they were worth the time to recommend them.
Hope this helps.
- Bringing Modern Weapons to a Fantasy World
- Rune Troopers
- Saving 80,000 Gold in Another World for My Retirement ( Has Millitary Content In It )
- Summon Japan