Recommended reading for folks who have the time:
Books
Starship Troopers by Robert Heinlein: Forget the movie. The movie has very little to do with the book. The movie is a travesty that will never be forgiven. Anyway.
Starship Troopers has been recommended reading for military personnel for decades. Not only is it a good look into the life and thoughts of your average grunt, the philosophies discussed in the book resonate strongly with a great many folks in the military. You might not agree with them, but it's a good way to understand the mindset.
The Forever War by Joe Haldeman: Often considered a rebuttal to
Starship Troopers, though the author would disagree. Takes a decidedly more pessimistic view on military life, focusing on the mental and physical toll of warfare. Addresses everything from idiotic command policies to dealing with losing comrades to the separation of enlisted and officers in everyday life.
Hammer's Slammers by David Drake: Most science fiction tends to be somewhat idealistic. Even the most horrific dystopian works where everyone dies are still, at the core, trying to impart a message. The series of short stories and novels that make up
Hammer's Slammers is one of the few that can genuinely be said to have no overarching morale or message. Instead, it's written with a historian's eye, which is fitting, considering the author is a historian. This is a world with precious few heroes. The protagonists are a mercenary outfit known as Hammer's Slammers. While there are a few reoccurring characters, most take center stage in a single story and, as often as not, die horribly.
Hammer's Slammers offers a truly unvarnished depiction of warfare. That means that no one is safe, and the difference between right and wrong is as simple as whether or not you're alive at the end of the day.
Honor Harrington series by David Weber: One part epic space opera, one part treatise on space warfare. The
Honor Harrington series is a must have for folks who want to better understand the tactics and strategy behind successful fleeting. There may very well be a more realistic take on the subject out there, but I've yet to find it.
Web
70 Maxims of a Maximally Effective Mercenary: Unless you feel like reading through 15 years of story from a webcomic that's been updated daily since 2000, I can't really recommend getting into
Schlock Mercenary. However, I can suggest looking up the 70 Maxims. In reality it's closer to 50 something, as several have yet to be revealed, but it's an entertaining and pragmatic list of maxims for those who want to write soldiers.
Skippy's List (213 Things No Longer Allowed in the US Army): One of the earliest examples of the internet spreading something far beyond its creator's original intent. Skippy's List is a humorous list of things that the author probably should have gotten the crap kicked out of him for trying (94. Crucifixes do not ward off officers, and I should not test that.) It's funny and dark and an excellent example of a soldier's sense of humor.