Because the book is a mishmash of genres, it makes sense that Tolstoy's writing style changes depending on what section he's working on. Whenever he launches into researched history mode, we get the detached, observant eye of a journalist. (And Tolstoy would know how to be that kind of military journalist, since he covered the Anglo-Russian Crimean War in the 1850s before writing War and Peace.)
When he starts doing the kind of macro analysis of the way the army works as an organization, he often borrows a trick from Homer (of Odyssey and Iliad fame), busting out an epic simile to get his meaning across. (Shmoop brain snack: an epic simile is basically a really, really long comparison between two things, using multiple characteristics.) One of the more famous ones is this passage that links the workings of an army to the workings of a mechanical clock:
Just as in the mechanism of a clock, so in the mechanism of the military machine, an impulse once given leads to the final result; and just as indifferently quiescent till the moment when motion is transmitted to them are the parts of the mechanism which the impulse has not yet reached. Wheels creak on their axles as the cogs engage one another and the revolving pulleys whirr with the rapidity of their movement, but a neighboring wheel is as quiet and motionless [until] the lever catches it and obeying the impulse that wheel begins to creak and joins in the common motion the result and aim of which are beyond its ken.
Just as in a clock, the result of the complicated motion of innumerable wheels and pulleys is merely a slow and regular movement of the hands which show the time, so the result of all the complicated human activities of 160,000 Russians and French--all their passions, desires, remorse, humiliations, sufferings, outbursts of pride, fear, and enthusiasm--was only the loss of the battle of Austerlitz, the so-called battle of the three Emperors--that is to say, a slow movement of the hand on the dial of human history. (188.8.131.52-9)
There are a lot of these extended comparisons in the book. Can you find others?
Another useful technique, at least for a narrator who usually likes to hang back from the action and not comment on what's going on, is to suddenly appear and give a pointed aside. Because he does it so rarely, it's pretty startling whenever the narrator's voice pops out at you.
Sometimes Tolstoy busts out this move for a moral lesson, like here: "On the twelfth of June, 1812, the forces of Western Europe crossed the Russian frontier and war began, that is, an event took place opposed to human reason and to human nature" (184.108.40.206). First, we've got facts ("twelfth of June," "war began"), and then – BAM – here comes the commentary: "an event opposed to human reason." Tell us how you really feel, Tolstoy.
Sometimes the stealth narrator is used for humor, like in this little scene between Napoleon and his assistant:
"I am very sorry to have made you travel so far," said Napoleon.
"Sire, I expected nothing less than to find you at the gates of Moscow," replied de Beausset. [...]
"Yes, it has happened luckily for you," he said, raising the open snuffbox to his nose. "You are fond of travel, and in three days you will see Moscow. You surely did not expect to see that Asiatic capital. You will have a pleasant journey." Beausset bowed gratefully at this attention to his (hitherto unknown to him) inclination for travel." (220.127.116.11-21)
Check out that "hitherto unknown to him." You gotta love that dig at how self-centered and oblivious Napoleon is, and how his subjects have to bow to the whims of such a powerful man. Awesome.
Finally, some of the style borrows a few things from an author Tolstoy really enjoyed reading –Charles Dickens. One of Dickens's main tricks for heightening his descriptions was to keep repeating one word over and over, but using it to refer to something new each time. Tolstoy does this in some places, like his use of the word "touching" in this passage:
After her talk with Pierre, Anna Mikhailovna returned to the Rostovs' and went to bed. On waking in the morning she told the Rostovs and all her acquaintances the details of Count Bezukhov's death. She said the count had died as she would herself wish to die, that his end was not only touching but edifying. As to the last meeting between father and son, it was so touching that she could not think of it without tears, and did not know which had behaved better during those awful moments--the father who so remembered everything and everybody at last and had spoken such pathetic words to the son, or Pierre, whom it had been touching to see, so stricken was he with grief, though he tried hard to hide it in order not to sadden his dying father. "It is touching, but it does one good. It uplifts the soul to see such men as the old count and his worthy son," said she. (18.104.22.168)
The effect is a little different though, and doesn't really build the passage's anxiety level like Dickens's use of this tool might. Instead, we get more of a sense that maybe Anna Mikhailovna is speaking really fast, too quickly to change up her language from one sentence to the next.