I thought I'd share one of my often-referenced sites on military ranks, insignias and abbreviations (Army does their shorthand differently than the other branches). This also shows lateral reference, i.e. an Army captain is not the same as a Navy captain. In fact, all the Navy (and Coast Guard) ranks are different than the others. It includes warrant officers, as well. For enlisted ranks see: Enlisted Ensignia Link. You may want to print a copy for your permanent reference materials.
Here's a little tidbit. At the top of the page, you'll see a series of links for W1, W2...O3, O4, etc. These are designation for rank. For instance, if someone says, "He's an O4 (oh four), they mean he's a Lieutenant Colonel (or Commander if Navy or Coast Guard). E1, E2, E3, etc. are enlisted ranks. O1, O2, O3 are commissioned officer ranks. W1, W2, etc. indicated warrant officer ranks. Using this jargon is good detail if your novels involve members of the military.
More trivia. A "full bird" is a colonel and designates a higher rank than a lieutenant colonel, though both are informally called "colonel." ("Full bird" refers to the eagle rank insignia for colonel.) A butter bar is a 2nd Lieutenant (newly commissioned officer), so dubbed for the single gold bar rank insignia.
It's interesting that a major outranks a lieutenant, but a lieutenant general outranks a major general.
You've heard a group of Army members say "Huah!" (or Hooah or Hwa!) That stands for Heard, Understood, Acknowledged. (Army has an acronym for everything.) It's generally used as an exclamation of support or enthusiasm for a statement made. Used in a sarcastic tone, it can also have a different meaning. (Head Up A**)