>>507875638
>Subterranean warfare is now part of the US army's focus for future conflicts
That's new to me. Didn't think Google would show up results about that but there are quite a lot of articles on this, though it appears the US only understand "subterranean" as just bunkers, tunnels and other concealed facilities instead of another dimension of battle
Here's a somewhat nice article:
https://www.usanca.army.mil/LinkClick.aspx?fileticket=8LDr6_KWWtc%3D&portalid=114