What film best captures what being in the military is truly like?

FULL METAL JACKET

“Best Years of our Lives“ I think best depicts the struggles many military have adjusting to civilian life. It’s filmed in the 40s but is a timeless story.

Accurately depicts... I feel like Jarhead is being wildly overlooked for its personal/mental grasp on the experience.
I’m not a Marine, but that movie in it’s entirety was uncomfortably relatable for me.
Sure, many of the glory/tribute films are awesome and also can be quite accurate. Band of brothers, Blackhawk Down, Saving Private Ryan, etc... are great for that.
Then there are the Hurt Locker and Pearl Harbor (Michael Bay) that may be entertaining, but have the accuracy of a blind pianist at a silent movie.

But hey, that’s just my opinion.

Heartbreak Ridge Gunny Highway. Old Corp. I watch it every time it comes on..

As an ex marine I'd say that " Full Metal Jacket " was the most accurate depiction of Marine Corps boot camp I've ever seen on screen. Of course R.Lee Ermey helped with that a great deal who at first was only there on the film set as an advisor but Kubrick had him take over the role of Hartman because Ermey actually WAS a Marine Corps drill instructor. And when I went through it in 1976 the drill instructors were just as mean and nasty and foul mouthed as anything. To add a little bit of spookiness to it all, when I was in 1st phase training I saw an MP truck with it's lights on heading out towards the rifle range at high speed. Apparently some recruit snuck a round off the range and shot himself during fire watch.

I would have to say the movie "Saving Private Ryan" was a good portrayal of military life. I would also say "To hell and back" with Audie Murphy (MOH) was a real good movie.

Down Periscope was one of the more accurate submarine movies believe it or not.

Rambo

Generation kill is pretty accurate.

The most realistic ambush scene I have seen in movies is from believe it or not Forrest Gump.