Of the 10,000 HDBTs identified, about 20 percent are estimated to have a major strategic function.
Over half of these strategic HDBTs are located near or in urban areas.
The number of known strategic HDBTs is increasing at a rate of about 10 percent per year. This increase is attributable mostly to discovery by the U.S. intelligence community and to a lesser extent to construction in countries seeking protection from U.S. military capabilities.
With the current U.S. nuclear arsenal, a number of the more important strategic HDBTs cannot be held at risk of physical destruction of the functional area.
A few hundred of the strategic HDBTs could be candidates for targeting with the robust nuclear earth penetrator (RNEP) weapon currently under study.
Examples of strategic HDBTs are shown in Figure 2.1 and detailed in this section. Representative actual overburdens, not their reinforced concrete equivalents, are described in the following examples.
Hard Target Type: Deep underground tunnel
Function: Deployment area for short-range ballistic missiles (SRBMs) that have a chemical weapon warhead; warhead mating performed in maintenance area
Site Location: Remote valley; nearest civilian population center is 30 kilometers away