The funny thing about this one is that, until recently, I thought I already knew the title and author of the novel in question! For many years, I honestly believed that what I am about to describe was the Poul Anderson novel called Tau Zero. But then I found myself reading something online about Poul Anderson's works which told me the general plot of Tau Zero, and it also mentioned that this was just an expanded version of one of his previously-published shorter pieces: "To Outlive Eternity." (I first read that one just a couple of years ago.)
So, since I now realize (after many years of confusion) that the book I am remembering was not Tau Zero, that means it may not have been written by Poul Anderson at all. So let's take inventory of what I still believe is accurate in my recollection (after more than 30 years).
To cover some incidentals first: I'm sure the version I read was a hardback, checked out from a public library, sometime in the range of 1982-1986. I think the book jacket, inside the plastic covering, had a lot of dark brown in the design, but I could be thinking of some other book. The story was in English, and I'm reasonably sure it wasn't a translation from some other language. If it wasn't by Poul Anderson, then I don't know who wrote it. (I'm certain I would have run across it again if it were by one of my favorite big-name SF authors of the mid-to-late 20th Century, such as Heinlein, Asimov, Niven, or Zelazny.)
Plot Points That I Can Remember:
The story is written in the third person. The main characters are humans aboard an interstellar vessel. They are already in mid-voyage as we first meet them in the opening chapter, so we don't actually see them get recruited and trained and gradually become acquainted with one another as newly-assigned shipmates. I think the entire crew of the ship is quite small -- say, less than twenty; maybe less than a dozen? (I'm sure that the number of human characters with significant speaking parts in the scenes set on the bridge was quite small, but it is possible that I am forgetting references to other people whose duties kept them elsewhere.)
There is a big war with an alien race. This has been going on for quite some time as the story opens. If I recall correctly, neither side has discovered any means of FTL travel, which means it can take years for news to reach Earth (or the alien homeworld) about any victories or defeats in other systems. The aliens seem to be our technological equals, or even somewhat superior. Near as I can recall, there is no indication that the aliens have ever shown any interest in negotiating and honoring a simple cease-fire, such as: "Let's let bygones be bygones. If you humans stay on this side of some lines we are drawing on star charts, we will reciprocate and leave your planets alone from now on." I think the aliens were seen (by humans) as the Nasty Aggressors who had started the bloodshed in the first place. I don't know if the aliens would have agreed with that.
The main scene that I remember came several chapters into the book. I believe the humans are doggedly pursuing some sort of assigned mission as part of the larger war effort, but their ship is currently flying solo; no allies anywhere in sight. In the bit I remember best, the humans on the bridge discover their current trajectory is taking them toward a large number of alien warships, and the human ship has already been accelerating for so long, therefore has built up so much momentum, that there's no chance of turning away and staying completely outside the enemy's effective range at this point. (I can't remember, though, if the enemy ships were moving fast on a collision course, or just sort of "hovering" at a preselected spot, waiting to see if any humans came along, or what.)
The best idea the humans can come up with is this:
Accelerate at 5 G's so that they will be going even more horrendously fast by the time they zip past the alien ships;
Fire off some missiles of their own when they are close to the aliens, partially in hopes of damaging or destroying at least a few of those ships, and partially to create the "fog of war" with all the explosions and stuff that will be happening all at once;
Cut their acceleration down to 1 G (I think) right after they have passed the alien formation, and pray that the aliens somehow lose sight of the ship's position during all the excitement. (I don't recall why "losing sight of them" would be likely to happen; maybe the humans actually cut all acceleration so that whatever they used as propulsion would no longer be making a big display of itself? Or maybe their propulsion method did not involve anything so blatant as a fusion flame?)
This tactic actually works -- pretty much. When the humans have either sharply reduced or completely ceased their acceleration, someone looking at instrument readouts says something along these lines: "A fireball of sequential nuclear explosions is up ahead of us. Measured relative to our own position, it is accelerating further away at approximately 4 G's." In other words, the aliens have fallen for it, and are having their computers launch missile after missile at selected points along the precise track the human ship ought to be following if it is still accelerating at 5 G's in the same direction as before, and if it has somehow survived the first few warheads aimed to intercept its calculated vector.
Just as the humans are starting to congratulate themselves, their teeth are rattled by a "near miss" which shakes their ship badly. After they recover, and conclude their ship is still functional, someone says (loosely paraphrased from my memory): "I think I understand what happened. At least one alien commander told himself that there was a logical possibility that we might have cut our acceleration back to our preferred 1 G just as we zipped past him, and so he fired at least one missile to intercept us if his suspicions were correct. But he missed us by a hair -- his math wasn't quite perfect in projecting our current course. I doubt he even expected to hit us with that shot; he was just covering all the bases."
No further shots come anywhere close to them (at this time). So it gradually becomes clear that they are now somehow "out of sight" of the alien fleet, and still getting further away every moment, and the plot continues from there. I think the scene I just described was no more than halfway through the book, but I can't remember what else happened. (For instance, what the human mission was supposed to be.) I am not sure I ever finished reading that library book; the situation was interesting, but I don't think I found the actual writing style (or the characters) to be especially appealing to my younger self.