This book does not use any of the characters or locations of the remainder of the series. While it can be read first (or alone), I would suggest reading the the other three books before reading this one. You'll have a better appreciation of all of them if you do, at least in my opinion.
The resemblance between this book and _Das Boot_ is purely coincidental. Glen had not seen nor heard of _Das Boot_ before he wrote this, he had not noticed the similarity even after, and he mentioned that the device of a journalist on military expeditions is fairly common.