The generic term “hard and deeply buried targets” refers to all types of intentionally hardened targets, either aboveground or belowground, that are designed to withstand or minimize the effects of kinetic weapons.
The generic term “underground facility” refers to all types of underground hardened structures and facilities regardless of their depth.
The generic term “hardened structure” refers to a structure that is intentionally strengthened to provide protection from the effects of kinetic weapons. All hardened structures can be further grouped into one of three types, defined by the location of the roof of the structure’s functional workspace:
Aboveground hardened structure. The roof of the functional workspace is above the ground surface. Included in this category are earth-bermed structures that are not exposed directly to weapons effects and for which air blast effects are reduced owing to the aerodynamic shape of the berm.
Shallow underground structure. The roof of the functional workspace is between the ground surface level and 20 meters deep.
Deep underground hardened structure. The roof of the functional workspace is covered by 20 or more meters of soil and/or rock.
The term “strategic hard and deeply buried target” refers to those HDBTs that perform a strategic function, such as command and control of military forces, protection of national leadership, WMD production or storage, and ballistic missile production, storage, or launch. The proposed nuclear earth-penetrator weapon (EPW) is being designed to defeat this target class.
Following is a concise list of background facts and estimates relating to HDBTs:
Potential U.S. adversaries worldwide are using underground facilities to conceal and protect their leadership, military and industrial personnel, weapons, equipment, and other assets and activities. These facilities include hardened surface bunkers and tunnel facilities deep underground.
Many underground command, control, and communications (C3) complexes and missile tunnels are between 100 and 400 meters deep, with the majority less than 250 meters deep. A few are as deep as 500 meters or even 700 meters, in competent granite or limestone rock.
As identified by the Defense Intelligence Agency, there are about 10,000 HDBTs in the territory of potential U.S. adversaries worldwide.