using the ranking system of the US during ww2 could we have private, private 2nd class, private 1st class, corporal, sergeant, staff sergeant, sergeant 1st class, master sergeant, 1st sergeant, 2nd lieutenant, 1st lieutenant, captain, major, lieutenant colonel, colonel, brigadier general, major general, lieutenant general and general also id like the icons too

You can already set custom ranks yourself, just look under startup options.

As for the icons, it's the same 4 repeated 3 times, just the color is a bit different (so 1, 5, 9 share an image, 2, 6, 10 share an image, etc.)
So a maximum of 12 ranks can have icons. Not sure what happens when your gun turrets achieve a higher rank without an icon.

As for using army ranks, it would make sense to only use [url=https://www.army.mil/ranks/#enlisted-ranks-title]enlisted ranks[/url] though, as gun turrets shouldn't be officers (they can't do anything other then shooting anyway :D) Would be really nice if people could create their own icon & rank packs for hero turrets :) That way, we could have localized army ranks :)