Editing Nuclear bunker buster (section)

== Methods of operation ==

=== Penetration by explosive force ===
[[Concrete]] structure design has not changed significantly in the last 70 years.{{citation needed|date=October 2022}} The majority of protected concrete structures in the US military are derived from standards set forth in ''[[Fundamentals of Protective Design]]'', published in 1946 (US Army Corps of Engineers). Various augmentations, such as [[glass]], [[fiber]]s, and [[rebar]], have made concrete less vulnerable, but far from impenetrable.

When explosive force is applied to concrete, three major fracture regions are usually formed: the initial crater, a crushed aggregate surrounding the crater, and "scabbing" on the surface opposite the crater. Scabbing, also known as [[spall]]ing, is the violent separation of a mass of material from the opposite face of a plate or slab subjected to an impact or impulsive loading, without necessarily requiring that the barrier itself be penetrated.

While soil is a less dense material, it also does not transmit shock waves as well as concrete. So while a penetrator may actually travel further through soil, its effect may be lessened due to its inability to transmit shock to the target.

=== Hardened penetrator ===
[[File:Secant ogive.svg|thumb|A secant ogive]]
Further thinking on the subject envisions a hardened penetrator using kinetic energy to defeat the target's defenses and subsequently deliver a nuclear explosive to the buried target.

The primary difficulty facing the designers of such a penetrator is the tremendous heat applied to the penetrator when striking the shielding at high speed. This has partially been solved by using metals such as [[tungsten]] (the metal with the highest melting point), and altering the shape of the projectile (such as an [[ogive]]).

Altering the shape of the projectile to incorporate an ogive shape has yielded substantial improvement in penetration ability. [[Rocket sled]] testing at [[Eglin Air Force Base]] has demonstrated penetrations of {{convert|100|to|150|ft|m}} in concrete {{Citation needed|date=March 2007}} when traveling at {{convert|4000|ft/s|m/s|abbr=on}}. The reason for this is [[liquefaction]] of the concrete in the target, which tends to flow over the projectile. Variation in the speed of the penetrator can either cause it to be vaporized on impact (in the case of traveling too fast), or to not penetrate far enough (in the case of traveling too slowly). An approximation for the penetration depth is obtained with an [[Impact depth|impact depth formula]] derived by [[Isaac Newton|Sir Isaac Newton]].

=== Combination penetrator-explosive munitions ===
Another school of thought on nuclear bunker busters is using a light penetrator to travel {{convert|15|to|30|m|ft|order=flip|sigfig=1}} through shielding, and detonate a nuclear charge there. Such an explosion would generate powerful shock waves, which would be transmitted very effectively through the solid material comprising the shielding (see "scabbing" above).