The Cold War is over and the U.S. government says it is no longer in the business of building new nuclear weapons.  So why is it deploying a versatile new kind of nuclear bomb intended to penetrate the earth and destroy underground facilities? 

This spring, the United States began fielding the first new nuclear capability added to the U.S. arsenal since 1989 -- a slim, 12-foot-long weapon known as the B61 "mod-11" gravity bomb.  It was developed and deployed without public or congressional debate, and in contradiction to official assurances that no new nuclear weapons were being developed in the United States.  The government contends the B61-11 is merely a "modification" to the B61-7 gravity bomb.  And yet, these modifications provide a substantial new military capability.  This is significant for three reasons: 

From a military standpoint, the B61-11 is uniquely able to destroy underground targets, and it can be set to do so with a small nuclear yield.  With such an underground blast, much of the resulting fallout might be relatively localized.  For these reasons, there are those who might be tempted to rationalize using the bomb.  Even before it was fully developed, it was used to threaten Libya over its construction of an alleged underground chemical weapons factory. 

From a diplomatic standpoint, this new weapon violates the spirit of the delicately forged international ban on nuclear testing.  And it further undermines the long-standing U.S. commitment to nuclear disarmament embodied in the Nuclear Non-Proliferation Treaty (NPT). 

From a development and production standpoint, the B61-11 may be the first such new capability, but it will not be the last.  It opens the way for other new weapons now under development in the Department of Energy's massive "stockpile stewardship and management program."  Current funding for this program exceeds the average spent by DOE during the Cold War.  Last month, nuclear pioneer Hans Bethe, joined by Frank von Hippel of Princeton and others, warned that some of this research could lead to entire new classes of weapons and should be stopped. 

But the B61-11 is a reality now, and raises fundamental questions about the sincerity of the U.S. commitment to the Comprehensive Test Ban Treaty (CTBT), signed by President Clinton last September and due to be considered for final ratification by the Senate this fall. 

While producing the B61-11 apparently did not involve modifications to the "physics package" -- the nuclear explosive itself -- there is no question that the bomb provides a new nuclear capability.  Although the treaty is silent on the question of new weapons, U.S. negotiators have explicitly said it is intended to prohibit such development. 

The B61-11 fulfills a longstanding desire of the military for an earth-penetrating weapon, a bomb that can get at command centers or other installations designed to be invulnerable to all but the largest nuclear weapons.  The previous weapon with this mission was the B53, the highest-yield weapon in the U.S. arsenal.  Although not a true earth penetrator, it was capable of taking out underground targets through brute force; a nine-megaton bomb makes a large crater.  The huge B53 weighs 8,900 pounds and can be delivered only by lumbering B-52 bombers. 

The smaller and lighter (1,200-pound) B61-11 can be delivered by the B-2A Stealth bomber, or even by F-16 fighters.  It is far more suitable for post-Cold War missions, penetrating as it does tens of meters into the earth and creating devastating shock waves with substantially less explosive power -- anywhere from just 300 tons to about 340 kilotons.  These lower yields are said to enhance its credibility as a deterrent. The B53, goes the tortured logic, was too big and too dirty to use.  It would cause massive "collateral damage" above ground -- or, in simpler language, the death of many innocent civilians.  The more modest B61-11 is considered relatively "useable" in such a context. 

But useable where?  What is the mission of the B61-11?  For years, nuclear planners sought to develop a weapon to hit deeply buried Soviet command-and-control centers.  But today Russia and the United States are no longer adversaries. 

Increasingly, U.S. nuclear strategists speak of holding targets at risk in "rogue states."  But since 1978, U.S. policy has expressly forbidden U.S. forces from using nuclear weapons against non-nuclear states that are signatories to the NPT, unless they are allied with a nuclear state engaged in an act of aggression.  Given this, the events surrounding the arrival of the B61-11 are, at best, difficult to explain. 

Interest in a B61-based earth penetrator appears to have been revived with an October 1993 request by Harold Smith, assistant to the secretary of defense for atomic energy, to explore alternatives to the B53.  On Nov. 29, 1994, the Nuclear Weapons Council Standing Safety Committee endorsed the B61 plan.  And on Feb. 6, 1995, Deputy Defense Secretary John Deutch signed off on it. 

On April 18, 1995, DOE submitted a classified request to six key members of Congress to find funds for the B61-11.  All necessary approvals were in hand by late July.  On Nov. 15, 1995, shortly after work on the B61-11 was formally approved, Smith requested that the schedule be accelerated.  He asked that the first unit be delivered "as soon as possible, with a goal of Dec. 31, 1996." 

The response from the nuclear labs was positive.  As the Los Alamos employee newsletter "Weapons Insider" put it: " NWT [the Los Alamos Nuclear Weapons Technology program] is committed to meeting the aggressive schedule, and a significant reprogramming of resources has allowed us to accelerate our progress." 

The project is one the labs are keenly interested in.  In recent years, some military strategists have advocated deployment and possible use of very small tactical nuclear weapons against Third World adversaries, especially in earth-penetrating roles.  Some of this advocacy -- perhaps most of it -- has come from the weapons labs.  In the fall 1991 issue of Strategic Review, for instance, Los Alamos strategists Thomas Dowler and Joseph Howard wrote:  "Would policymakers employ nuclear weapons to protect U.S. contingency forces if conventional weapons proved inadequate, or would the nature of our present nuclear arsenal `self-deter' policymakers from using those weapons? 

"One possible answer to these questions might be the development of nuclear weapons of very low yields...The existence of such weapons -- weapons whose power is effective but not abhorrent -- might very well serve to deter a tyrant who believes that American emphasis on proportionality would prevent the employment of the current U.S. arsenal against him. 

"We doubt that any president would authorize the use of the nuclear weapons in our present arsenal against Third World nations.  It is precisely this doubt that leads us to argue for the development of subkiloton weapons." 

In July 1992, Los Alamos conducted a high-level briefing called "Potential Uses for Low-Yield Nuclear Weapons in the New World Order."  One theme of the briefing was that in future showdowns with Third World states, "we need options besides defeat or use of inappropriately large [nuclear] weapons." 

One option, suggested the briefing, was to develop and deploy "micronukes" with a yield of some 10 tons of high explosives; "mininukes" with a yield of 100 tons; and "tiny nukes" with a yield of 1,000 tons.  An earth penetrator with a yield of just 10 tons could, according to a Los Alamos briefing chart, "hold buried leadership and C3 at risk."  And it could do that while keeping "collateral damage very localized."  Translation:  You could threaten to blow up an enemy's headquarters bunker and disrupt his command, control and communications without destroying the surrounding area.  Why did Smith insist in November 1995 on setting such "aggressive deadlines" for the B61-11 project?  Perhaps the answer can be found in a series of statements offered the following spring by administration officials, including Defense Secretary William Perry.  On March 28, 1996, Perry testified in the Senate in support of the Chemical Weapons Convention.  At one point, he said:  "We have an effective range of alternative capabilities to deter or retaliate against use of the CW [chemical weapons].  The whole range would be considered ...We have conventional weapons, also advanced conventional weapons -- precision guided munitions, Tomahawk land-attack missiles -- and then we have nuclear weapons."  A few days later, Robert Bell of the White House National Security Council spoke about the United States having signed on to the African Nuclear-Weapon-Free-Zone (ANWFZ) Treaty, a treaty that Libya had signed.  "Each party pledges not to use or threaten to use nuclear weapons against an ANFWZ party.  However, [the treaty] will not limit options available to the United States in response to an attack by an ANWFZ party using weapons of mass destruction." 

At a breakfast meeting with defense writers, Smith went further.  He was quite specific regarding the possible preemptive use of nuclear weapons.  He spoke of the potential menace presented by a Libyan chemical weapons factory under construction underground at Tarhunah, 40 miles southeast of Tripoli.  At present, said Smith, the United States had no conventional weapon capable of destroying the plant from the air, and such a weapon would not be ready in less than two years. However, by the end of the year, the United States would have a nuclear warhead based on the B61 that would be able to do the job. 

At the same time, administration officials began hedging on the "no-first-use" pledge that President Clinton had reaffirmed only a year earlier.  When arms-control advocates questioned this apparent change in attitude, the Pentagon tried to clarify matters.  At a press briefing on May 7, 1996, Defense Department spokesman Kenneth Bacon said there had been some "confusion" in the press regarding the issue.  "Should military options be necessary [against Libya], we can accomplish this with conventional means.  There is no consideration to using nuclear weapons and any implication that we would use nuclear weapons against this plant preemptively is just wrong." 

"Preemptively" seems to have been the operative word at the May 7 briefing.  Bacon also reiterated that the United States for years had reserved the right to respond with "devastating force" if weapons of mass destruction were ever actually used "against us or our forces." 

Bacon went on to quote Perry, who said on April 26 at Maxwell Air Force Base:  "In every situation that I have seen so far, nuclear weapons would not be required for response.  That is, we could have a devastating response without the use of nuclear weapons, but we would not forswear that possibility." 

Whatever message the administration spokesmen were trying to send regarding the nuclear option, work on the B61-11 project continued on schedule.  At the same time, President Clinton was signing the test-ban treaty.  That treaty bans nuclear testing, but does not specifically address weapons development or new deployments.  However, stopping new weapons is clearly a part of the treaty's intent. 

Consider, for example, a January 1996 statement made in Geneva by John Holum, director of the U.S. Arms Control and Disarmament Agency, as he pushed for completion of the CTBT:  "Even the open literature points to a broad array of new weapons developments...Many would involve directed energy weapons -- ways to focus the release of energy with greater precision than is now possible, to enable military effects well beyond those available now.  Without nuclear testing, the nuclear weapon states will not be able to pursue confidently such technologies as the nuclear-explosion-pumped X-ray laser, the so-called nuclear shotgun, enhanced electromagnetic pulse weapons, microwave weapons, and enhanced radiation weapons...And the true zero [yield] test ban will also place out of reach new `mininuke' and `micronuke' concepts. 

"So let there be no mistake -- the CTBT will help impede the spread of nuclear weapons.  But its great practical impact will also be for arms control -- to end development of advanced new weapons and keep new military applications from emerging." 

The B61-11 may be a mere modification, a new shell for an older physics package.  It may not be the kind of exotic new weapon that Holum listed.  But it is a weapon with a new capability.  Should the need arise, it will allow U.S. military forces -- to borrow Holum's words -- to "focus the release of energy with greater precision," in a "new military application." 

Why was it developed and deployed now?  That's a question the Clinton administration needs to answer.  Because the real "collateral damage" of new weapons like the B61-11 is likely to occur not in wartime, but much sooner, through devaluation of the treaties and commitments upon which the fragile non-proliferation regime rests. 

Greg Mello directs the Los Alamos Study Group, a nuclear weapons policy research and education organization located in Santa Fe.  This article is adapted from one that appears in the May/June issue of the Bulletin of the Atomic Scientists.

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