I’ve mentioned this before with regard to your character’s occupation. This goes slightly beyond that to the entire story environment if all or even part of your story takes place in the military. Most of us know someone who has been in some branch of the military. Of course they all have their own personality and in some cases rank designation. For example, the lowest rank differs for all of them, though some, such as the Army and Air Force start to overlap as they go up the ranks. The Navy is different all around.

Make sure you use rank, terminology, and dialog correctly. Rank is easily checked online. Terminology is a bit more of a challenge and should be given a sanity check by someone who knows. Authenticity adds to the flavor and credibility of your story while missing the mark erodes your credibility as a writer.