As I alluded to here, I am a firm believer that dice rolling and rules exist for two reasons. 1) To fill in all the extra flavor you as the DM just aren’t inspired to, or didn’t have time to get to, and 2) to provide agency to the player in the collaborative storytelling art that is roleplaying. What really turned me off to 3rd Ed was the rules for every situation, much as what one would find wargaming. Who had time to create house rules, when $1500 bucks and 20 source books later you needed an abacus to keep track of all the modifiers that were “official rules.”
I actually really liked the mixed dice mayhem of 1st and 2nd Ed. due to the fact it allowed for far more granular seeming control of the results, gave the players plenty of things to obsess over (1D8 damage or 1D4+2, etc), and created a flavor to the game that was unique. When D20’s were really only used to roll attacks, and D10’s were imitative, you could create tension in the narrative just with a deliberate selection of a single die to fiddle with as the DM. Players would lay out their dice in “battle order” if they suspected things might be dicey (pun intended), etc. I do miss that quiet a lot actually now that I think about it. Upon further reflection I appreciate system that allow that kind of totemic prop for player participation.
Back to the matter at hand, military focused RPG’s. I have in my library SpyCraft, I never player it and honestly I don’t recall if the system seemed decent or not. It is however modern at least.
Some other I spotted on my shelves that would work, the Palladium system (Rifts, Macros, Robotech, etc all the same system which apparently is officially the Megaversal system). Not the worlds greatest system, but very workable and pretty refined having been around in one guise or another for several decades as the this point. Most of the settings are distinctly military/combat in nature so it handles it well. As an aside, I always like Rifts, it was a neat setting.
There is also GURPS, which has plethora of either modern or military related supplements released for it. I was never a huge fan of the actual system personally, but that is apparently just me considering how successful it’s been.
DP9’s Silhouette system was paired with two of my favorite sci-fi settings with Heavy Gear and Jovian Chronicles (god bless Ebay, I bought every single source book for Jovian Chronicles for $19 shipped in one lot). The idea was to be able to use both table top miniatures for combat as a stand alone war game, and integrate the RPG element in. With a good GM who doesn’t go for rules lawyering it’s an extremely fast system that I quiet liked. It allowed for a focus on the action and story telling. Now if you try to use the table top war game rules for Jovian Chronicles, pack a lunch, a calculator, and then realize you should have just bought Attack Vector instead. Also DP9 has the Gear Krieg universe which is great fun WW2 super science action gaming both as a table top game, as an RPG.
Lastly is The Riddle of Steel, the only RPG to ever be endorsed by the Historical European Martial Arts Alliance. It is a VERY granular system where combat is involved, and has a pretty decent magic system as well. Obviously it’s focus is on hand to hand combat, but the expansion Flower of Battle I believe has more detailed ranged combat rules, that could be extrapolated to firearms if one wished. As a practitioner of both eastern and western martial arts, it does capture the reality of that type of encounter. It is also rather cumbersome and unsatisfying in result. Yes the reality is two similarly equipped and experienced folks facing off with pointy things, is that they both end up seriously hurt. I don’t RP for reality, I play for the cinematic. However if dirty, nasty, brutish and short is you aesthetic, then you may enjoy it more.
And once again when I get started talking about gaming I go full nerd.