A very tense but enjoyable read, NG! There's not much I can add to the comments already made, but I applaud you for making the effort to provide plausible physics behind the ship's fields. So often, sci-fi writers (myself included) have a tendency to just come up with treknology that is based more on fantasy and cool-sounding words. I found that your explanation was subtle but also "real." It seemed to fit the narrative without over-shadowing the plot.
You definitely had a submarine warfare feel going. I was reminded most of the novel, "Run Silent-Run Deep." I thought the tactics you employed in this segment made perfect sense.
Now as to whether they actually survive
or not . . .