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Earth Penetrating Warheads Against Deep Targets


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Earth Penetrating Warheads Against Deep Targets

 

FAS.org

 

The Administration is requesting funds from Congress for exploring the feasibility of a Robust Nuclear Earth Penetrator, or RNEP. “Robust” means that the nuclear bomb will be able to penetrate some distance into hard rock before exploding. The RNEP is being pursued in response to the worldwide proliferation of deeply buried targets.

 

The Federation of American Scientists (FAS) has just completed a study, “Earth Penetrating Warheads against Deep Targets,” that examines arguments for the RNEP, analyses countermeasures, and calculates the consequences of using an RNEP. We find it comes up short on all accounts.

 

The study finds that the tactical justifications for the RNEP are inconsistent and unrealistic. The RNEP is required only if we need to destroy deep underground facilities. We will detect deep tunnels only by detecting the entrances. The entrances can be attacked with precision conventional weapons and sealed up. Conventional weapons can attack the power lines and communication links going in, the air and water supply, and the cooling system. RNEP is needed only if sealing up the entrances and isolating the facility, a so-called “functional defeat,” with conventional weapons is not adequate. For some reason the facility at the end of the tunnel has to be destroyed.

 

But consider the types of targets that the threat analysis suggests might be in deep tunnels. They are production or storage facilities for chemical, biological or nuclear weapons or protected hiding places or communications centers for military or civilian leadership. All of these targets can be divided into one of two categories. The first category, for example, a uranium enrichment facility or a communications center or a storage site for bulk chemical weapons, is effectively neutralized if it can be cut off by attacking the entrances with conventional weapons. The other category, for example, assembled nuclear bombs or a national leader in hiding, is small and easily moved and would not be in a vulnerable bunker to begin with. In the first case, destroying the entire tunnel is unnecessary; in the second case it is ineffective.

 

The FAS study also considered one particular countermeasure: digging deeper. It turns out that even if we want to attack deep targets, we cannot always do it. Any enemy can easily dig deep enough that even nuclear weapons can’t reach. RNEP is presented as being essential because so many potential enemies have built underground facilities that are just out of reach of our conventional weapons. This is no coincidence. Precision-guided weapons have made any surface target vulnerable, therefore nations have dug into rock for protection. How deep do they dig? As deep as they must to get beyond the reach of conventional weapons, then they stop. But there is no technical limit to digging deeper until they are out of reach of even extremely powerful nuclear weapons. Digging tunnels a kilometer deep in granite is not technically challenging and even megaton weapons cannot reach them. In these cases, whether we like it or not, we are going to be forced to go back to attacking the entrances to tunnels, which can be done with conventional weapons.

 

The FAS study looked at the consequences of using nuclear earth penetrators. There are two important misconceptions about nuclear earth penetrators that must be corrected to understand the aftereffects of a nuclear earth penetrator attack.

 

The first misconception is that the weapons will penetrate far into the earth to attack the deep target directly. This is not true. No weapon will penetrate more than ten or twenty meters into hard rock. But these few meters are critical. With a surface explosion, most of the energy of the bomb goes into a shockwave in the air. Buried just several meters, most of the energy goes into a shockwave in the earth. But it is the shockwave that goes down to destroy the target, not the bomb. The bomb is close to the surface and those few meters of rock will do nothing to contain the radioactivity. A huge cloud of radioactive fallout will spread dangerous levels of radiation over hundreds of square miles.

 

The second misconception confuses RNEP with the Administration’s exploration of concepts for small nuclear weapons. The RNEP is not a small weapon. The two candidate RNEP systems are the B61, with a yield estimated at 320 thousand tons of TNT, and the B83, with a yield estimated at 1.2 million tons of TNT. The B83 would blast out a crater over a thousand feet across and, if used in North Korea, would send a plume of radioactive fallout as far as Japan. Because it is the shockwave, not the bomb that goes down into the earth to destroy the buried facility, enormously powerful bombs are required. Smaller weapons simply do not have the reach.

 

RNEP looks appealing for attack of deeply buried targets because of the fallacy of the last move. Nations started digging to escape attack by precision-guided conventional weapons and they can simply dig some more in response to nuclear weapons. But there are other tactics, namely attacking the entrances and cutting off communication with the outside, achieving a functional defeat. This can be accomplished with current and planned conventional weapons.

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NAS Report on Nuclear Earth Penetrators Estimates Huge Human Costs, Overstates Need for the Weapons

 

Contact : Ivan Oelrich (ioelrich@fas.org)

 

FAS.org

 

On 27 April, the National Academy of Science (NAS) released the summary and conclusions of a long-awaited report Effects of Nuclear Earth Penetrator and Other Weapons. The damage calculated by the Academy panel is sobering, with projected casualties exceeding one million people.

 

The decision of whether or not the United States should further pursue nuclear earth penetrating weapons needs to be based on a comparison of costs and benefits. While the Academy study indicates the unacceptable consequences of the nuclear program, it also exaggerates its benefits. Specifically:

 

“Conclusion 1. Many of the more important strategic hard and deeply buried targets (HDBTs) are beyond the each of conventional explosive penetrating weapons and can be held at risk of destruction only with nuclear weapons. Many—but not all—known and/or identified hard and deeply buried targets can be held at risk of destruction by one or a few nuclear weapons.”

While this statement is technically correct, it contains hidden assumptions that mischaracterize the current and future military problem and potential solutions. First, it is true that there are hundreds of deeply buried targets that are important and just out of reach of U.S. conventional earth penetrators. However, this is exactly the situation we should expect to find.

 

Nations around the world started digging in response to technical developments in precision guided weapons - developments that rendered virtually any fixed target on the surface vulnerable to air attack. But digging costs money.

 

So how deep should a nation dig? They will dig until they get beyond the reach of existing earth penetrators, add a bit for a safety margin, and stop. The result is the collection of targets we see today.

 

This makes nuclear weapons appear particularly attractive. There is an array of targets, just barely out of reach, that we can destroy with the greater power of a nuclear explosion. Yet, nuclear earth penetrators will not change the measure-countermeasure dynamic.

 

A recent study by the Federation of American Scientists (FAS) shows that any nation that can tunnel under a hundred meters of hard rock can tunnel under a thousand meters of hard rock. There is no great technical challenge to digging down to depths of a kilometer or so.

 

The NAS study calculates that even a one megaton warhead will not be able to reliably destroy targets under just 300 meters of rock. If the U.S. begins work on nuclear earth penetrators, then countries will respond exactly the way they responded to conventional earth penetrators. They will restart digging.

 

Long before a nuclear earth penetrator is deployed, targets will be located more than 300 meters deep, just out of range of the nuclear weapon. The U.S. will have lost all the benefits that non-proliferation restraint would have won us, and we will be in exactly the same position we are in today.

 

The conclusion also implicitly accepts the key premise that the tunnel must be destroyed, not just isolated. For some reason, sealing the entrances with conventional weapons and cutting off the power, air, cooling, and water are not adequate. The tunnel must be crushed.

 

This objective is not plausible for real targets. For example, one of the targets explicitly mentioned in the NAS study are missile tunnels. If we can seal the entrance with conventional explosions, the missile will not be able to go anywhere and we will have accomplished what the military calls a “functional” defeat. The missile might not be destroyed but it is no longer capable of fulfilling any useful military mission.

 

Some may counter that the tunnel could be dug out again. This is true and it could be attacked again with conventional weapons. If they can dig out the tunnel again, they could build a missile again. No attack has permanent effects, it just buys time. The only way to insure that an enemy does not rebuild destroyed weapons is to occupy the country or install a friendly regime, in which case we need neither conventional nor nuclear bombs, we can send in engineers to dismantle the buried facility. Finally, since digging deeper to be out of reach of even nuclear weapons is straightforward, we will have no choice in many cases except to seal up the entrances and that can be done with conventional weapons.

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