june 24 2018
Army spent $572 million to train 26 brigades out of 31 to be able to fight underground.
1500 to 4000 troops per brigade = 39,000 to 104,000 troops trained to fight underground.
TC 3-20.50
"Small Unit Training in Subterranean Environments," published in November 2017. "Though prepared through an 'urgent' development process, it is authorized for immediate implementation."