The Apocalypse Troll

"USN Vs. UFOs"

Stand-alone military science fiction book by David Weber, also known for his Honor Harrington works.

Follows the adventures of the Russian descended Time Traveling Super Soldier Colonel Ludmilla Leonovna chasing the Big Bad back in time to stop The End of the World as We Know It from happening.

The whole book is available online, on Baen Books.

Tropes associated with Colonel Ludmilla Leonovna herself:
 * Action Girlfriend
 * Ace Pilot: As of the beginning of the book, Ludmilla has thirty-four fighter kills and squadrons under her command have destroyed thirteen capital ships, including a dreadnaught which she was the Sole Survivor of the battle to destroy it. She kills at least one Troll Fighter after scrambling (maybe a second one, but the narrative doesn't confirm that her missile hit). Following that the Troll commander notes that, in the three week long running battle during which her fighter is the only remaining human craft because she hasn't had to sleep, she has killed another ten fighters from his squadron. She's an ace nine times over even before she takes out two more Trolls on atmospheric approach to Earth.
 * Badass: In his first viewpoint passage, the Troll recognizes that her fighter  has performed exceptionally since the battle began. He automatically acknowledges that she is what his masters call a "cralkhi"   and that she is an extremely dangerous foe. This just makes him want to kill her even more.
 * Badass Bookworm: She has three advanced degrees.
 * Eternal English: Slightly subverted - some bits from 400 years in the future require explanation, such as dropping the first syllable of "mister" and just saying "Ster".
 * Mayfly-December Romance: Ludmilla (who is effectively immortal via Healing Factor, though she can be killed) falls in love with a normal man.
 * For certain values of "normal"...
 * Punny Name: Ludmilla's fighter is named
 * Really Seven Hundred Years Old: Looks 18-19, is actually.
 * The Symbiote: The source of her superhuman reflexes, strength, Healing Factor and apparent youth. Can be passed to others via blood transfusion, but since it has a 95 to 99% death rate (depending on the available medical technology), this is never done except in desperation, when the person receiving it would die anyway.
 * And if you read that and started wondering about mosquitoes, that question is explicitly raised in the book as well. Answer: it kills the mosquitoes pretty much instantly, before they have a chance to bite someone else and pass it on.
 * Likewise, if you haven't guessed that, you need to read this wiki more.
 * Take Me to Your Leader: The second sentence she says to Dick (after "Hello, yourself") after waking up. It's an Invoked Trope because she's from the future, literally fell from space, has an interest in "historical" entertainment, and (as she explains when Dick calls bullshit on her using this line) has a low brow sense of humor.
 * Take Me to Your Leader: The second sentence she says to Dick (after "Hello, yourself") after waking up. It's an Invoked Trope because she's from the future, literally fell from space, has an interest in "historical" entertainment, and (as she explains when Dick calls bullshit on her using this line) has a low brow sense of humor.

Tropes associated with the rest of the book:
 * Absolute Xenophobe: the Kangas. The Trolls, judging by the sample of one we have, go past this and into Omnicidal Maniac territory.
 * The Kangas are genocidal religious fanatics and the Trolls are their cyborg slaves which also happen to be "programmed" to be psychotic aside from absolute loyalty to their masters. The Trolls are very aware of their enslavement and hate their Kanga masters just as much as everything else (see the Omnicidal Maniac entry below).
 * Exclusively Evil: the Trolls, every single one.
 * Blood Knight: While Trolls are best described as Omnicidal Maniacs, they do delight in destroying the objects of their all consuming hatred.
 * The Trolls are portrayed in the book as especially hating Ludmilla and her kind.
 * Brain In a Jar: Trolls are psychotic lab grown human brains that are installed into war machines. They're even interchangeable, as
 * The Dragon: Blake Taggart.
 * Dying Moment of Awesome: Captain Onslow ordering Ludmilla to pursue the fleeing Kangas with all of her surviving fighters instead of returning to protect the Defender because he's already given orders to ram the Troll dreadnaught. He nicely caps it off with the words "See You in Hell, Col-" as the flagships collide in a titanic explosion.
 * Humans Through Alien Eyes: We're only told (not shown) how Kangas think, but the Troll viewpoint is almost as alien. Their foes deliberately try to not think of them as at all human.
 * Mind Rape: The Troll does this to several people in order to acquire information about present-day Earth. One victim is a schoolteacher who was camping with her husband; it has its way with her for six hours before finally disposing of her body, and records every moment of the process for its later enjoyment.
 * Mysterious Antarctica: where the Troll first lands on Earth.
 * Omnicidal Maniac: The Trolls would gladly kill their alien masters if they could, but the Kangas made very sure they can't. So they'll settle for killing everything else.
 * When humans first found out that Trolls were cloned human cyborgs they set a trap to isolate and rescue a few of them. The Trolls slaughtered the peaceful envoys attempting to make contact, even though it was clear that they were completely outgunned by said envoys' military guards. They just tried to kill as many as they could before being taken out themselves.
 * See You in Hell: literally Captain Onslow's last words, spoken to Ludmilla as the Defender rams the Troll dreadnaught. Both ships are completely annihilated in a huge nuclear fireball.
 * Sole Survivor: Ludmilla and the Troll are the only survivors of a pair of Standard Sci-Fi Fleet battle groups that spent about a month (subjective time, at least, considering that they spent most of that time traveling at relativistic speeds) wiping each other out both before and after they went so fast they went back in time.
 * Standard Sci-Fi Fleet: The general organization of both the Terran Navy and the Kangas. The shorthanded human battle group is led by the Defender, which ends up facing off against a Kanga carrier and dreadnaught, after both sides' cruisers and destroyers were destroyed before the big ships managed to defy Einstein.
 * Temporal Paradox: After some early discussion, the question is tabled in favor of more practical matters. The upshot is that it doesn't really matter; even if Ludmilla's home timeline is safe, she and her comrades would fight just as hard to save another Earth from what the Kangas and their cyborg slaves would do to it.
 * Terminator Twosome: Ludmilla and the Troll, each the Sole Survivor of their respective forces.