In Passage at Arms, Glen Cook transplants submarine warfare, as it was practiced during World War II, to a science-fictional setting in the far future, using an engaging mix of speculative technology, humor, and nuts-and-bolts realism. Humanity has discovered faster-than-light hyperdrive and has been using it to colonize other star systems. Our sphere of expansion eventually clashes with that of an alien race from Ulant. War is the result, and as Ulant has an edge on Earth both technologically and numerically, it is a war we are losing. Earth has only one advantage to even the odds - the Climbers.
Climbers are small warships carrying a variety of weaponry, missiles being their most effective armament. They are too small to stand toe-to-toe and slug it out with even the smallest of the enemy's warships, but they do have one advantage - they can Climb. A once-in-a-millennium accident leads humanity to the discovery of a layer above (or around, or within, or perpendicular to - no one really knows) hyperspace. This layer is called null-space, or simply "null". A ship in null is insulated from the rest of the universe. It becomes effectively invisible, except for a tiny, almost indetectible shadow it casts into hyperspace. The Climber is blind while in the null, although it can maneuver in hyperspace by dead reckoning.
Like the submarines of WWII, Climbers are used mainly to attack enemy supply convoys, popping out of null just long enough to launch an attack, then climbing back into null in an effort to evade pursuit by enemy warships. The Climber's time in null is limited partly by its fuel supply, but more acutely by its need to vent heat, which it can not do while in null. This limitation leads to cat-and-mouse confrontations with squadrons of Ulant warships called hunter-killers, analogous to WWII destroyers.
The story is told in the first person by a journalist who is travelling as an observer on a Climber mission, given a temporary military commission as a lieutenant for the duration. The journalist's name is never mentioned - he is addressed only as "Lieutenant" by the crew. He is an old friend of the ship's captain, who's name is also never revealed - he is known only as the "Commander", or "the Old Man". The rest of the crew is named or nicknamed, and we come to know them well through the Lieutenant's eyes as the mission progresses, along with all of the personality quirks resulting from the stress of long periods of excruciating boredom, and short, sharp bouts of intense fear.
Cook combines his speculative technology with a knowledgeable realism concerning soldiers, warfare, and the stress of combat. His attention to detail and personal style of writing combine to build a sustained dream that carries the reader along through a well-crafted adventure. The book has long been out of print, and can only be found in used book stores. This is unfortunate, for in my view Passage at Arms deserves to stand among the classics of military science fiction.