"The Time Mercenaries" is a 1968 science-fiction novel by Philip E. High, and was published as one half of an Ace Double, with the other side being Anthropol, by Louis Trimble. "The Time Mercenaries" is a shorter novel, at 113 pages, and like many of High's stories, explores dystopia and social engineering, but it is also a fast-moving war story.
The story starts when a submarine, commanded by a Captain Randall who will be our protagonist, is seemingly hit by a destroyer during exercises. Mysteriously, the crew find their submarine okay, and return to port. There, they learn the truth: they actually were hit, and ended up embalmed for over a thousand years, to be revived by future medical science. The people of the future have a problem: after centuries of war, humanity decided to genetically suppress all forms of violence. This seemingly utopic society was seemingly doing fine, until an alien race of bug eyed monsters (quite literally, an alien race that resembles bees) attacks, and humanity has no way to fight---besides by reviving the ancient submarine and sending one submarine crew against an alien armada. Using robots and future technology, the small crew has to fight off an alien race that reproduces at a prodigious rate. And in doing so, they will inevitably disrupt the seemingly-pacifistic society in which they live.
I liked this book for several reasons. The first is, as a science-fiction story, it started with a single high concept: "How would a pacifistic society deal with war?" and followed it to a logical conclusion, with some interesting side issues presented as well (such as sentient robots and alien biology). One problem is that, as with many Ace Doubles, the story seems to be too edited, and the difference between Captain Randall leading a single submarine and commanding an intergalactic armada skips over intervening parts. I also wonder if certain themes were topical --- being written in 1968, the idea of a pacifistic society being untenable might have been a direct reference to the cold war--- in which case the book might be taken as propaganda. However, I prefer to look at it as a science-fiction book with a strong concept, good action, and only a few flaws in the execution.