In 2012, the US intelligence community estimated over 10,000 potential underground facilities exist worldwide, with the majority of them unidentified and the expectation that their numbers will continue to increase dramatically over the next decade.

Countries across the world increasingly recognize the benefit underground facilities provide in protecting and securing strategic assets. These facilities are becoming "ubiquitous," able to conceal resources, capabilities, and intent. High on the list of nations making significant investments in underground facilities is China, whose underground tunnel network reportedly stretches 5,000 km.China's underground facilities are emblematic of the US HBDT (Hard and Deeply Buried Target) defeat problem, highlighting gaps in intelligence (represented by the operational capability elements of detect, characterize, plan and assess) and weapons capability ( represented by the operational capability element of defeat).