We had this book for the bookgroup in May. It's the first book in a series, not that any of us plan to read any of the sequels. It's set in WWII and it starts in a US ship, just about to be destroyed by a giant Japanese ship. This is 70% of the book (I was reading with my Kindle) and it's only after this part that there's science fiction. That 70% is not bad for a war book, but it wasn't SF.
They try hard to escape the Japanese ship and dash into what is sort of a fantasy ocean area and come through on the other side where, yes, the only humans that have come through are like them, and most of them have been killed already.
There are two main aliens there -- a cat-like peaceful group, whom they teach a lot of science and engineering -- and scary-shaped critters who kill everybody they see, even their own type of critter. The old falling-apart US ship goes after the critters and then help the cat-like folks. There's a clear lead to the next book.
So far, I've been picking well on the bookgroup books that I get for the Kindle, so I don't have to add them to my shelves (and pay more for them).