A nuclear bunker buster,[1] also known as an earth-penetrating weapon (EPW), is the nuclear equivalent of the conventional bunker buster. The non-nuclear component of the weapon is designed to penetrate soil, rock, or concrete to deliver a nuclear warhead to an underground target. These weapons would be used to destroy hardened, underground militarybunkers or other below-ground facilities. An underground explosion releases a larger fraction of its energy into the ground, compared to a surface burst or air burst explosion at or above the surface, and so can destroy an underground target using a lower explosive yield. This in turn could lead to a reduced amount of radioactive fallout. However, it is unlikely that the explosion would be completely contained underground. As a result, significant amounts of rock and soil would be rendered radioactive and lofted as dust or vapor into the atmosphere, generating significant fallout.
While conventional bunker busters use several methods to penetrate concrete structures, these are for the purpose of destroying the structure directly, and are generally limited in how much of a bunker (or system of bunkers) they can destroy by depth and their relatively low explosive force (compared to nuclear weapons).
The primary difference between conventional and nuclear bunker busters is that, while the conventional version is meant for one target, the nuclear version can destroy an entire underground bunker system.
The main principles in modern bunker design are largely centered around survivability in nuclear war. As a result of this both American and Soviet sites reached a state of "super hardening", involving defenses against the effects of a nuclear weapon such as spring- or counterweight-mounted (in the case of the R-36) control capsules and thick concrete walls (3 to 4 feet (0.91 to 1.22m) for the Minuteman ICBM launch control capsule) heavily reinforced with rebar. These systems were designed to survive a near miss of 20 megatons.[citation needed]
Liquid-fueled missiles such as those historically used by Russia are more fragile and easily damaged than solid-fueled missiles such as those used by the United States. The complex fuel storage facilities and equipment needed to fuel missiles for launch and de-fuel them for frequent maintenance add additional weaknesses and vulnerabilities. Therefore, a similar degree of silo "hardening" does not automatically equate to a similar level of missile "survivability".[citation needed]
Major advancements in the accuracy and precision of nuclear and conventional weapons subsequent to the invention of the missile silo itself have also rendered many "hardening" technologies useless. With modern weapons capable of striking within feet (meters) of their intended targets, a modern "near miss" can be much more effective than a "hit" decades ago. A weapon need only cover the silo door with sufficient debris to prevent its immediate opening to render the missile inside useless for its intended mission of rapid strike or counter-strike deployment.[citation needed]
A nuclear bunker buster negates most of the countermeasures involved in the protection of underground bunkers by penetrating the defenses prior to detonating. A relatively low yield may be able to produce seismic forces beyond those of an air burst or even ground burst of a weapon with twice its yield.[citation needed] Additionally, the weapon has the ability to impart more severe horizontal shock waves than many bunker systems are designed to combat by detonating at or near the bunker's depth, rather than above it.
Geologic factors also play a major role in weapon effectiveness and facility survivability. Locating facilities in hard rock may appear to reduce the effectiveness of bunker-buster type weapons by decreasing penetration, but the hard rock also transmits shock forces to a far higher degree than softer soil types. The difficulties of drilling into and constructing facilities within hard rock also increase construction time and expense, as well as making it more likely construction will be discovered and new sites targeted by foreign militaries.[citation needed]
Methods of operation
Penetration by explosive force
Concrete structure design has not changed significantly in the last 70 years.[citation needed] The majority of protected concrete structures in the U.S. 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, fibers, 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 spalling, 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
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 unit when striking the shielding (surface) at hundreds of meters per second. 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 100 to 150 feet (30 to 46m) in concrete [citation needed] when traveling at 4,000ft/s (1,200m/s). 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 formula derived by Sir Isaac Newton.
Combination penetrator-explosive munitions
Another school of thought on nuclear bunker busters is using a light penetrator to travel 15 to 30 meters 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).
Policy and criticism of fallout
The main criticisms of nuclear bunker busters regard fallout and nuclear proliferation. The purpose of an earth-penetrating nuclear bunker buster is to reduce the required yield needed to ensure the destruction of the target by coupling the explosion to the ground, yielding a shock wave similar to an earthquake. For example, the United States retired the B-53 warhead, with a yield of nine megatons, because the B-61 Mod 11 could attack similar targets with much lower yield (400 kilotons),[citation needed] due to the latter's superior ground penetration. By burying itself into the ground before detonation, a much higher proportion of the explosion energy is transferred to seismic shock[2] when compared to the surface burst produced from the B-53's laydown delivery. Moreover, the globally dispersed fallout of an underground B-61 Mod 11 would likely be less than that of a surface burst B-53. Supporters note that this is one of the reasons nuclear bunker busters should be developed. Critics claim that developing new nuclear weapons sends a proliferating message to non-nuclear powers, undermining non-proliferation efforts.[who?]
Critics also worry that the existence of lower-yield nuclear weapons for relatively limited tactical purposes will lower the threshold for their actual use, thus blurring the sharp line between conventional weapons intended for use and weapons of mass destruction intended only for hypothetical deterrence, and increasing the risk of escalation to higher-yield nuclear weapons.[3]
Local fallout from any nuclear detonation is increased with proximity to the ground. While a megaton-class yield surface burst will inevitably throw up many tons of (newly) radioactive debris, which falls back to the earth as fallout, critics contend that despite their relatively minuscule explosive yield, nuclear bunker busters create more local fallout per kiloton yield.[citation needed] Also, because of the subsurface detonation, radioactive debris may contaminate the local groundwater.
The Union of Concerned Scientists advocacy group points out that at the Nevada Test Site, the depth required to contain fallout from an average-yield underground nuclear test was over 100 meters, depending upon the weapon's yield. They contend that it is improbable that penetrators could be made to burrow so deeply. With yields between 0.3 and 340 kilotons, they argue, it is unlikely the blast would be completely contained.
Critics further state that the testing of new nuclear weapons would be prohibited by the proposed Comprehensive Test Ban Treaty. Although Congress refused to ratify the CTBT in 1999, and therefore this treaty has no legal force in the US, the US has adhered to the spirit of the treaty by maintaining a moratorium on nuclear testing since 1992.[4]
Proponents, however, contend that lower explosive yield devices and subsurface bursts would produce little to no climatic effects in the event of a nuclear war, in contrast to multi-megaton air and surface bursts (that is, if the nuclear winter hypothesis proves accurate). Lower fuzing heights, which would result from partially buried warheads, would limit or completely obstruct the range of the burning thermal rays of a nuclear detonation, therefore limiting the target, and its surroundings, to a fire hazard by reducing the range of thermal radiation with fuzing for subsurface bursts.[5][6] Professors Altfeld and Cimbala have suggested that belief in the possibility of nuclear winter has actually made nuclear war more likely, contrary to the views of Carl Sagan and others, because it has inspired the development of more accurate, and lower explosive yield, nuclear weapons.[7]
As early as 1944, the Barnes Wallis Tallboy bomb and subsequent Grand Slam weapons were designed to penetrate deeply fortified structures through sheer explosive power. These were not designed to directly penetrate defences, though they could do this (for example, the Valentin submarine pens had ferrous concrete roofs 4.5 metres (15 feet) thick which were penetrated by two Grand Slams on 27 March 1945), but rather to penetrate under the target and explode leaving a camouflet (cavern) which would undermine foundations of structures above, causing it to collapse, thus negating any possible hardening. The destruction of targets such as the V3 battery at Mimoyecques was the first operational use of the Tallboy. One bored through a hillside and exploded in the Saumur rail tunnel about 18m (59ft) below, completely blocking it, and showing that these weapons could destroy any hardened or deeply excavated installation. Modern targeting techniques allied with multiple strikes could perform a similar task.[8][9][10]
Development continued, with weapons such as the nuclear B61, and conventional thermobaric weapons and GBU-28. One of the more effective housings, the GBU-28 used its large mass (2,130kg or 4,700lb) and casing (constructed from barrels of surplus 203mm howitzers) to penetrate 6 meters (20 feet) of concrete, and more than 30 metres (98 feet) of earth.[11] The B61 Mod 11, which first entered military service after the Cold war had ended, in January 1997, was specifically developed to allow for bunker penetration, and is speculated to have the ability to destroy hardened targets a few hundred feet beneath the earth.[12]
While penetrations of 20–100 feet (6.1–30.5m) were sufficient for some shallow targets, both the Soviet Union and the United States were creating bunkers buried under huge volumes of soil or reinforced concrete in order to withstand the multi-megaton thermonuclear weapons developed in the 1950s and 1960s. Bunker penetration weapons were initially designed within this Cold War context. One likely Soviet Union/Russian target, Mount Yamantau, was regarded in the 1990s by Maryland Republican congressman, Roscoe Bartlett, as capable of surviving "half a dozen" repeated nuclear strikes of an unspecified yield, one after the other in a "direct hole".[13][14]
The Russian continuity of government facility at Kosvinsky Mountain, finished in early 1996, was designed to resist US earth-penetrating warheads and serves a similar role as the American Cheyenne Mountain Complex.[15][16] The timing of the Kosvinsky completion date is regarded as one explanation for US interest in a new nuclear bunker buster and the declaration of the deployment of the B-61 Mod 11 in 1997. Kosvinsky is protected by about 300meters (1000feet) of granite.[17]
The weapon was revisited[dubious–discuss] after the Cold War during the 2001 U.S. invasion of Afghanistan, and again during the 2003 invasion of Iraq. During the campaign in Tora Bora in particular, the United States believed that "vast underground complexes," deeply buried, were protecting opposing forces. Such complexes were not found. While a nuclear penetrator (the "Robust Nuclear Earth Penetrator", or "RNEP") was never built, the U.S. DOE was allotted budget to develop it, and tests were conducted by the U.S. Air Force Research Laboratory. The RNEP was to use the 1.2megaton B83 physics package.[18]
The Bush administration removed its request for funding[19] of the weapon in October 2005. Additionally, then U.S. SenatorPete Domenici announced funding for the nuclear bunker-buster has been dropped from the U.S. Department of Energy's 2006 budget at the department's request.[20]
While the project for the RNEP seems to be in fact canceled, Jane's Information Group speculated in 2005 that work might continue under another name.[21]
A more recent development (c. 2012) is the GBU-57 Massive Ordnance Penetrator, a 30,000pound (14,000kg) conventional gravity bomb. The USAF's B-2 Spirit bombers can each carry two such weapons.
Notable US nuclear bunker busters
Note that with the exception of strictly earth penetrating weapons, others were designed with air burst capability and some were depth charges as well.
A bunker buster is a type of munition that is designed to penetrate hardened targets or targets buried deep underground, such as military bunkers.
The GBU-28 is a 4,000-pound (1814.3 kg) class laser-guided "bunker busting" bomb produced originally by the Watervliet Arsenal, Watervliet, New York. It was designed, manufactured, and deployed in less than three weeks due to an urgent need during Operation Desert Storm to penetrate hardened Iraqi command centers located deep underground. Only two of the weapons were dropped in Desert Storm, both by F-111Fs. One GBU-28 was dropped during Operation Iraqi Freedom. It was designed by Albert L. Weimorts.
The effects of a nuclear explosion on its immediate vicinity are typically much more destructive and multifaceted than those caused by conventional explosives. In most cases, the energy released from a nuclear weapon detonated within the lower atmosphere can be approximately divided into four basic categories:
A mushroom cloud is a distinctive mushroom-shaped flammagenitus cloud of debris, smoke, and usually condensed water vapour resulting from a large explosion. The effect is most commonly associated with a nuclear explosion, but any sufficiently energetic detonation or deflagration will produce a similar effect. They can be caused by powerful conventional weapons, like thermobaric weapons such as the ATBIP and GBU-43/B MOAB. Some volcanic eruptions and impact events can produce natural mushroom clouds.
Samuel Theodore Cohen was an American physicist who is generally credited as the father of the neutron bomb.
The B83 is a variable-yield thermonuclear gravity bomb developed by the United States in the late 1970s that entered service in 1983. With a maximum yield of 1.2 megatonnes of TNT (5.0 PJ), it has been the most powerful nuclear weapon in the United States nuclear arsenal since October 25, 2011 after retirement of the B53. It was designed by Lawrence Livermore National Laboratory.
The B61 nuclear bomb is the primary thermonuclear gravity bomb in the United States Enduring Stockpile following the end of the Cold War. It is a low-to-intermediate yield strategic and tactical nuclear weapon featuring a two-stage radiation implosion design.
The B43 was a United States air-dropped variable yield thermonuclear weapon used by a wide variety of fighter bomber and bomber aircraft.
The Mk/B53 was a high-yield bunker buster thermonuclear weapon developed by the United States during the Cold War. Deployed on Strategic Air Command bombers, the B53, with a yield of 9 megatons, was the most powerful weapon in the U.S. nuclear arsenal after the last B41 nuclear bombs were retired in 1976.
Laydown delivery is a mode of delivery found in some nuclear gravity bombs: the bomb's descent to the target is slowed by parachute so that it lands on the ground without detonating. The bomb then detonates by timer some time later. Laydown delivery requires the weapon to be reinforced so that it can survive the force of impact.
The T-12 earthquake bomb was developed by the United States from 1944 to 1948 and deployed until the withdrawal of the Convair B-36 Peacemaker bomber aircraft in 1958. It was one of a small class of bombs designed to attack targets invulnerable to conventional "soft" bombs, such as bunkers and viaducts. It achieved this by having an extremely thick, hardened nose section designed to penetrate deeply into hardened concrete structures and then detonate inside the target after a short time delay.
The GBU-57A/BMassive Ordnance Penetrator (MOP) is a precision-guided, 30,000-pound (14,000 kg) "bunker buster" bomb used by the United States Air Force. It is substantially larger than the deepest-penetrating bunker busters previously available, the 5,000-pound (2,300 kg) GBU-28 and GBU-37.
A tactical nuclear weapon (TNW) or non-strategic nuclear weapon (NSNW) is a nuclear weapon that is designed to be used on a battlefield in military situations, mostly with friendly forces in proximity and perhaps even on contested friendly territory. Generally smaller in explosive power, they are defined in contrast to strategic nuclear weapons, which are designed mostly to be targeted at the enemy interior far away from the war front against military bases, cities, towns, arms industries, and other hardened or larger-area targets to damage the enemy's ability to wage war. As of 2024, no tactical nuclear weapons have ever been used in combat.
The Mark 8 nuclear bomb was an American nuclear bomb, designed in the late 1940s and early 1950s, which was in service from 1952 to 1957.
The W86 was an American earth-penetrating nuclear warhead, intended for use on the Pershing II intermediate-range ballistic missile (IRBM). The W86 design was canceled in September 1980 when the Pershing II missile mission shifted from destroying hardened targets to targeting soft targets at greater range. The W85 warhead, which had been developed in parallel with the W86, was used for all production Pershing II missiles.
The B61 Family is a series of nuclear weapons based on the B61 nuclear bomb.
The Mark 11 nuclear bomb was an American nuclear bomb developed from the earlier Mark 8 nuclear bomb in the mid-1950s. Like the Mark 8, the Mark 11 was an earth-penetrating weapon, also known as a nuclear bunker buster bomb.
The earthquake bomb, or seismic bomb, was a concept that was invented by the British aeronautical engineer Barnes Wallis early in World War II and subsequently developed and used during the war against strategic targets in Europe. A seismic bomb differs somewhat in concept from a traditional bomb, which usually explodes at or near the surface and destroys its target directly by explosive force; in contrast, a seismic bomb is dropped from high altitude to attain very high speed as it falls and upon impact, penetrates and explodes deep underground, causing massive caverns or craters known as camouflets, as well as intense shockwaves. In this way, the seismic bomb can affect targets that are too massive to be affected by a conventional bomb, as well as damage or destroy difficult targets such as bridges and viaducts.
A strategic nuclear weapon (SNW) refers to a nuclear weapon that is designed to be used on targets often in settled territory far from the battlefield as part of a strategic plan, such as military bases, military command centers, arms industries, transportation, economic, and energy infrastructure, and countervalue targets such areas such as cities and towns. It is in contrast to a tactical nuclear weapon, which is designed for use in battle as part of an attack with and often near friendly conventional forces, possibly on contested friendly territory.
The Disney bomb, also known as the Disney Swish, officially the 4500 lb Concrete Piercing/Rocket Assisted bomb was a rocket-assisted bunker buster bomb developed during the Second World War by the British Royal Navy to penetrate hardened concrete targets, such as submarine pens, which could resist conventional free-fall bombs.
References
Clifton, James R, Penetration Resistance of Concrete: A Review, The Physical Security and Stockpile Directorate, Defense Nuclear Agency.
Ernest, Jonathan V; etal. (2005), Nuclear Weapon Initiatives: Low-yield R&D, Advanced Concepts, Earth Penetrators, Test Readiness, Nova Publishers, ISBN1-59454-203-1 .
Moore, RT, Barrier Penetration Tests, National Bureau of Standards.
Woolf, Amy F (2005), U.S. Nuclear Weapons: Changes In Policy And Force Structure, Nova Science Publishers, Incorporated, ISBN1-59454-234-1 .
Gsponer, Andre (31 March 2007), The B61-based "Robust Nuclear Earth Penetrator:" Clever retrofit or headway towards fourth-generation nuclear weapons?, Independent Scientific Research Institute, arXiv:physics/0510052, Bibcode:2005physics..10052G .
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