quality of the intelligence that exists or will exist. Nor does the committee discuss how good the intelligence must be to enable the effective operational use of a weapon.

The discussions and calculations presented in this report assume knowledge of the target’s location, purpose, size, function, internal layout, and other relevant features at the time it may be attacked. This assumption of perfect, timely intelligence is unlikely to hold in reality for the vast majority of targets of interest.

Important to the issue of finding, identifying, and characterizing a target is that, in addition to concealment, deceptive techniques are used extensively by adversaries to complicate matters. The calculations presented should all be viewed with these intelligence uncertainties in mind.

Weapon-System Survival and Arrival at the Target

In addition to the passive defense of hardening a target, high-value sites are generally defended. Thus, the method of delivery of a weapon is important. For example, defenses against a weapon that is air-delivered are quite widespread, whereas ballistic missile defenses are virtually nonexistent. This report does not examine the effectiveness of delivery modes or defenses against them.

Weapon Penetration and Detonation

There is the need to consider the probability that an earth-penetrator weapon (EPW) will survive ground penetration, penetrate to the desired depth, and then successfully detonate. In comparison with surface (contact) burst weapons, the EPW experiences more rigorous impact conditions. These factors are discussed in Chapter 3.

In the following discussion of weapons effects at depth, the committee presumes that the nuclear earth-penetrator weapon successfully reaches the target, penetrates any aboveground covering structure and possible defenses, and enters the surface to a depth sufficient to couple the majority of its energy to the ground, all with a probability of 1.0. The committee did not study the probability of any of these events.

Energy Coupling of Nuclear Weapons Effects to the Ground

The energy coupled by a nuclear weapon to the ground is expressed as the fraction of the total weapon yield converted to kinetic energy of downward-moving solid or nonvaporized ground material. The amount of energy coupled to the ground is strongly dependent on the weapon’s actual height of burst (HOB) or depth of burst (DOB), as well as on nuclear design details (i.e., yield-to-mass ratio, fission fractions, and relative coupling efficiencies of the source components). Geologic properties also play a role.

Effects Manual-1: Capabilities of Nuclear Weapons1 of the Defense Threat Reduction Agency (DTRA) (formerly the Defense Nuclear Agency) defines an equivalent yield factor for both total coupled energy and ground-shock-coupled energy as a function of HOB/DOB (see Appendix C in this report for details). Figure 4.1 shows the equivalent yield factors normalized to a contact burst using the DTRA-recommended, scaled HOB of 0.05 m/kt1/3. Note that the coupled energy is not defined for a scaled HOB greater than −0.05 m/ktl/3 or a scaled DOB greater than 0.05 m/kt1/3 due to uncertainties in calculations for this near-surface region. The ground-shock-coupled energy2 includes surface air-blast-induced ground shock.

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