The future of nuclear weapons might not be huge and mega destructive but smaller, tactical, and frighteningly, more common. The U.S. Air Force is investigating more options for “variable yield” bombs — nukes that can be dialed down to blow up an area as small as a neighborhood, or dialed up for a much larger punch.

The Air Force currently has gravity bombs that either have or can be set to low yields: less than 20 kilotons. Such a bomb dropped in the center of Washington, D.C., wouldn’t even directly affect Georgetown or Foggy Bottom. But a Minuteman III missile tipped with a 300-kiloton warhead would destroy downtown Washington and cause third-degree burns into Virginia and Maryland.

Throughout much the Cold War, the thinking in Washington and especially Moscow was that bigger yields was better: the more destruction, the more deterrence. This thinking drove the Soviet Union to build the most powerful bomb ever, the Tzar Bomba, whose 100,000 kilotons, detonated over DC, would burn Baltimore.

But the future of nuclear deterrence lies, at least in part, in smaller nuclear weapons that the United States might actually use, Air Force Gen. Paul Selva, the Vice Chairman of the Joint Chiefs of Staff, said Thursday at a Mitchell Institute event in downtown Washington. The threat of mutually assured destruction doesn’t work against smaller regimes in the way that it used to against the Soviet Union. Selva said the U.S. needs to be able launch a nuclear attack on an adversary without ending the world or causing massive “indiscriminate” casualties.

“If all you have is high-yield weapons to answer a low-yield attack, it’s still a nuclear attack. Answering that with a conventional weapon is likely not going to have the kind of deterrent value as saying, ‘Even if you use a low-yield weapon, we have options to respond,” he said. “If the only options we have are to go with high-yield weapons that create a level of indiscriminate killing that the President can’t accept, then we haven’t presented him with an option with an option to respond to a nuclear attack in kind.”

The United States is amid a massive modernization of its nuclear arsenal, including work on defining requirements for a new ICBM. In December, the Defense Science Board urged the Pentagon to incorporate low-yield and variable-yield reentry vehicles into future ICBM designs. Selva said Thursday that the Air Force had not yet made a final decision on that.

“Whether we do it with a ballistic missile or re-entry vehicle or other tool in the arsenal, it’s important to have variable-yield nukes,” he said.

The military has a requirement to explore such systems, mandated by several nuclear posture reviews and "that is a path we’re pursuing very quickly," he said.

But Congressional critics who say the proliferation of such weapons would bring less, not more security.

“I have no doubt the proposal to research low-yield nuclear weapons is just the first step to actually building them,” Sen. Dianne Feinstein, D-Calif., told Roll Call in February. “I’ve fought against such reckless efforts in the past and will do so again, with every tool at my disposal.”

She also sounded a skeptical note against ‘tactical nukes in general. “There’s no such thing as limited nuclear war, and for the Pentagon’s advisory board to even suggest such a thing is deeply troubling.”

The U.S. military is not the only one that is envisioning the use of smallish nukes in combat. While Russia possesses the largest-yield nuclear weapons, it also boasts much smaller, “tactical” nuclear weapons that it’s used in exercises. And has not foresworn the first use of nuclear weapons in a conflict. In fact, Russian lawmakers have threatened the use of low-yield nuclear weapons were NATO forces to attack pro-Russian forces in Eastern Ukraine.

North Korea claimed last year to have tested a hydrogen bomb, which would have a potential yield between 15,000 and 50,000 kilotons, but analysis of underground North Korean missile tests showed that the yield on the test device was closer to 10 kilotons, more like a regular fission bomb.

Hans Kristensen, director of the Nuclear Information Project at the Federation of American Scientists, points out that the United States already has nuclear bombs that can be converted to low-yield weapons. And it may be building more. The controversial Long-Range Standoff Cruise missile will use a modified W80 nuclear warhead.

“The rumor is that they want to modify that warhead to improve the selection of lower-yield options,” said Kristensen. “Military leaders have talked about the LRSO mission as very ‘tactical’ or ‘war-fighting’ terms,” he said, highlighting this piece for the Union of Concerned Scientists.

“The still-unanswered question is why there would be a need for a low-yield warhead on ballistic missiles. What are the strikes that existing warheads can’t do, where would the President be self-deterred because of too big yield, where has the intelligence community concluded that adversaries would get an advantage and deterrence (or war fighting) would fail if we didn’t have low-yield, and why can existing capabilities not adequately hold at risk the same targets? Many questions, few answers.” said Kristensen.