This article is from June of 2018.
https://taskandpurpose.com/news/army-subterranean-warfare-training/
The Army Is Spending Half A Billion To Train Soldiers To Wage War Underground - Task & Purpose
Editor’s Note: This article by Matthew Cox originally appeared onMilitary.com, the premier source of information for the military and veteran
https://taskandpurpose.com/news/army-subterranean-warfare-training