It’s been called the most dangerous nuclear weapon in America’s arsenal. Not the biggest — that distinction goes to the 1.2-megaton B83 bomb — but a weapon whose precision makes it the most likely to be used in an actual war. It’s called the B61 gravity bomb, built to be dropped from an airplane, with a variable yield that can detonate with an explosive force of up to 11 times the force of the Hiroshima blast, or be dialed down to a tiny fraction of that size.

Specially designated B61 bombs, 150 of them based in Europe, are what’s left of America’s deployed “tactical” nuclear arsenal, the low-yield weapons designed to be used in battle rather than delivered by long-range missile or strategic bomber. During the Cold War, that stockpile held as many as 7,000 weapons — B61s, short-range ballistic missiles, artillery shells and even nuclear landmines. The drastic reduction in tactical nuclear weaponry is one of the triumphs of post-Cold War arms limitations — a reduction that makes the world safer without any cost to deterrence.

However, to the horror of arms control supporters on the right and left, that may be about to change. Some in Washington have begun calling for America to build and deploy new nuclear weapons and be prepared to fight all-out nuclear wars. In a recent report, the Pentagon’s Defense Science Board recommends “a more flexible nuclear enterprise” that could include a “tailored nuclear option for limited use” and “lower yield, primary-only options.” With President Donald Trump’s call to “expand” the U.S. nuclear arsenal, there is a growing possibility that these recommendations could turn into reality.

Defense hawks argue that new, small nuclear weapons deployed in Europe would further deter Russian aggression in the region — and that they are critical for “winning” a nuclear war. This is a profoundly flawed argument. Though it might seem that adding nuclear weapons makes the U.S. more secure, the introduction of new low-yield tactical nuclear weapons — the exact weapons that the U.S. has successfully eliminated almost completely from its arsenal — would have exactly the opposite effect: It would severely weaken U.S. national security by lowering the threshold for the use of nuclear weapons, making the unthinkable more likely, and further destabilizing an already fraught U.S.-Russia relationship.

In President Ronald Reagan’s 1984 State of the Union address, he eloquently declared: “a nuclear war cannot be won and must never be fought.” This statement continues to ring true. As most nuclear strategists and experts make clear, nuclear weapons exist to deter an adversary; if they were actually used, the result would be a catastrophe with no winner. As former Defense Secretary William Perry has argued, even a single nuclear detonation would have dire social and political consequences “beyond what people understand.” However, unlike their strategic nuclear counterparts, low-yield nuclear weapons do not establish deterrence. In fact, they undermine it.

As it stands today, the threshold for nuclear use is rightfully very high. Perry argues that there are virtually zero plausible scenarios in which the United States would need to initiate a nuclear first-strike. New low-yield weapons, however, could dangerously lower the threshold for using a nuclear weapon first. Due to their particular capabilities, retired Gen. James Cartwright, the former top commander of U.S. nuclear forces, has stated that smaller nuclear weapons are “more thinkable” in combat. Gen. Norton Schwartz, the former U.S. Air Force chief of staff, is on the record saying that a smaller nuclear weapon with “improved accuracy and lower yield is a desired military capability,” strongly implying that they would serve a role beyond deterrence.

This type of thinking is extraordinarily risky. The use of just one small nuclear weapon would almost certainly trigger a like-for-like retaliation, followed by a similar or stronger response from the original aggressor and progression toward a nuclear apocalypse. The assumption that crossing the nuclear threshold can lead to anything other than colossal destruction puts hundreds of millions of lives at risk. Deputy Defense Secretary Robert Work echoed this point in 2015, arguing, “Anyone who thinks they can control escalation through the use of nuclear weapons is literally playing with fire. Escalation is escalation, and nuclear use would be the ultimate escalation.”

Oddly, supporters of new tactical nuclear weapons fully understand these consequences. They often justify their proposals by citing Russia’s tactical arsenal and Moscow’s supposed “escalate to de-escalate” policy, whereby the Russian military would detonate small nuclear weapons in conflict to force its opponent — i.e. NATO — to back down (the existence of this Russian policy is an open question). New U.S. tactical nuclear weapons, they say, would deter Russia from even considering such an option.

In reality, our current conventional and strategic nuclear capabilities already deter Russia from initiating even a limited nuclear strike. The United States has called attention to the ability of our strategic nuclear weapons to strike any target on Earth. If rational, Russia knows full well that any attempt to escalate would not end with de-escalation. If not rational, no deployment of new nuclear weapons will ever deter the Kremlin.

Deploying new, more capable low-yield weapons would serve only to heighten tensions between the United States and Russia, likely leading to a new type of nuclear arms race that no one would win, and increasing the chances that these arms will be used. The benefits are nonexistent; the heightened dangers are impossible to ignore. As Reagan made clear, once the nuclear threshold is crossed, there is no going back.

Philip E. Coyle is the senior science fellow at the Center for Arms Control and Non-Proliferation. He served in top security roles in the Clinton and Obama administrations and previously was a top official at the Lawrence Livermore National Laboratory. James McKeon is a policy analyst at the Center for Arms Control and Non-Proliferation.

Authors: