re: DUMBS, Underground Warfare >>8638223

"expects underground fighting to become not merely an add-on issue for the US, and said it might emerge as the primary playing field for combat."

"Special Assistant to the US Army Judge Advocate-General Michael Meier told the conference that North Korea has around 5,000 out of the 10,000 tunnels and bases underground worldwide.

He said that North Korea and other countries do not merely build tunnels. Rather, they build sometimes vast underground facilities under mega cities where pursuers can get lost in a byzantine maze of utilities pipelines and subway lines"

https://www.jpost.com/Opinion/Military-Affairs-The-next-underground-war-611509

"Last year, the U.S. Army accelerated its push to outfit 26 of its 31 active combat brigades with new tools and training to “fight in large-scale subterranean facilities that exist beneath dense urban areas around the world,” Military.com reported"

https://www.defenseone.com/technology/2018/06/underground-may-be-us-militarys-next-warfighting-domain/149296/