In spirit, I loved military and historical themed RPG's. Some of my favorites included Skull and Crossbones, Privateers and Gentlemen, and of course Boothill (okay, not "military" but not sci-fi or fantasy, either). In practice, however, my gaming group sadly learned that "realistic" games required a completely different way of playing. The hack-n-slash and spell-throwing tactics that worked so well for dungeon brawls just didn't cotton in historical or military games, and more often than not, everyone in our band of pirates/royal navy sailors/outlaws ended up bleeding-out about 3 encounters into any scenario. Sure...Tomb of Horrors had it's sphere of annihilation, but every damn grenade, rpg, rocket or bazooka was a flying sphere of annihilation in T2K; every Colt .45 or shotgun was a +10 magic missile, and never was there a cleric or healing potion to be had. In short, military and history themed RPG's taught us how to play carefully and cautiously, and that in an RPG, discretion is very often the better part of valor.
Historical RPG's also taught me something else: the importance of good story-telling. Many of the fantasy and Sci-fi games we played had very little story to them (or perhaps better said, story that we cared about) aside from hack-n-slash adventuring. In the historical / military RPG's, we usually had to figure something out, make a (sometimes complicated) plan or decision, or struggle with a moral complexity. Although these games were often less bloody, they were more engaging and somehow more human.
Although I haven't played a game of this ilk for sometime, I look fondly upon games like "Carry", "In Harm's Way", or "Aces in Spades".
Yours in gaming,
Jack Nastyface