"Arc of Fire" is another set of rules you might consider, morrisbh. This one isn't too well known. I've played in a couple of games of it at our regional miniatures convention. I think I'm going to use it myself (already bought two copies) when I get around to 20mm WW2 and some early 20th Century actions in Africa and China. Here's 5 key factors to consider:
1. The book cost is only $20 from Brigade Games (charts in rules can be photocopied)
2. Authors not trying to sell a bunch of supplement books to increase your investment
3. Covers any action in the 20th Century
4. Designed for players to handle between 10 and 150 figures each (squad to company).
5. Uses d10 instead of d6 (I don't think d6 gives adequate room for modifiers)
Here's the link on Brigade Games:
https://www.brigadegames.com/Arc-of-Fire-Rules_p_2074.htmlHere's an old review from 13 years ago on BoardGameGeek:
https://boardgamegeek.com/thread/27043/user-reviewHaving said all that about Arc of Fire, you could also use Pulp Alley for even smaller actions, such as sabotage of a bridge (as in "For Whom the Bell Tolls" or "Force 10 from Navarone"), or a prison camp rescue, or a small scouting mission, or a spy scenario. Pulp Alley is not really military, but it doesn't require super heroes or villains or wierd stuff or horror. You can make it look military depending on how the adventure scenario is set up and the figures that you use.
Here's a review on BoardGameGeek:
https://boardgamegeek.com/thread/1261637/pulp-alley-gets-it-rightHere's the website:
https://pulpalley.com/