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.