Science fiction novel from 1980s or 1990s or 2000s. People can go into a particular different space, said to be "above" our space, where distances are shorter. Particular ships can go "up" into this space and move undetected, and can shoot and kill ships in normal space. Novel describes a patrol by one such ship. Reporter who has wrangled a tour on this on this ship witnesses successful military activity and crew undergoing various hair-raising situations and privations. Self consciously based on WWII submarine novels and nonfiction such including Run Silent, Run Deep and real life WWII actions such as Darter and Dace.
This is Passage at Arms
As confirmed by the querent, the novel Passage at Arms is the answer to this question.
There's a "reporter":
The reporter, the observer, ideally, remains neutral and detached. However, I’ve altered the experiment simply by being here. I’ve tried to be both remote and intimate, born Climber man and reporter. I’ve failed. My shipmates, so young, came to Navy with near-virgin pasts. Trying to mirror then: innocence, I’ve kept my own past fairly private.
And a kind of superspace :
Hyperspace, where the Newtonian and Einsteinian rules break down, is the rind of the orange. Fine and dandy. Now friend Diekereide grips the orange like a baseball and throws the hard slider. He tells me the rind exists everywhere coequal with the universe it contains. An orange that is part rind all the way to the pips. Relates back to the curvature of space, where, if you head off on a straight line and stick with it long enough, you get back to where you started. Only, using Reinhardt’s math, you can take shortcuts because in hyperspace every point touches every other point. In perfect hyperspace, which seems to be as mythical as perfect vacuum, you can travel the light years between point A and point B in no elapsed time.