Low-Yield Nukes Are Still Dangerously Destructive

When most people think about nuclear weapons, they think about “the bomb”: a unitary, solitary warhead of terrible power. Actual nuclear weapons have historically come in all shapes and sizes and were designed for different uses.

The possibility of Russia using a “tactical” and “low-yield” weapon has been in the news a lot over the past few months, as has U.S. interest in having “tactical” and “low-yield” weapons at its disposal. These terms are dangerously deceptive in that they imply that weapons on par with the bomb that destroyed Hiroshima are in some way less monstrous and more safely usable than they are.

The two major categories that have historically been used to describe weapons ­are “tactical” and “strategic.” The differences are less about the technology than the intent: a “strategic” weapon is one allocated to a “strategic” target. This category includes any target where the mere targeting is likely to reduce an enemy’s willingness to enter a war. The actual use of the weapon will reduce their ability to make war in a broad sense.

“Strategic” weapons could be pointed at centers of population, economic activity, political activity, and the military bases and weapons that an opponent might use to wage strategic warfare back on you (including, notably, an enemy’s nukes, if they have them).

“Tactical” weapons are intended to be used against “tactical” targets: tanks on the battlefield, bombers or fighters in the skies, submarines and boats deployed at sea, and troops in the field. Tactical nuclear weapons can be considered “theater” nuclear weapons deployed in the actual area where direct fighting occurs.

In terms of the technological differences, imagine a Venn diagram, with a small number of weapons being inherently “tactical” (in that they would be hard to use against strategic targets by their very nature, like a nuclear depth charge) and some being firmly “strategic” (in that they would be too large to imagine credibly using in a way that would limit the damage to a battlefield), but with many weapons straddling both definitions, capable of being used in either application, depending on where they were aimed.

Most tactical weapons are considered “low-yield,” which means their explosive power (measured in thousands of tons of TNT equivalent) is relatively low compared to other nuclear weapons. They are still mind-bogglingly large explosions most of the time.

To put things in perspective, consider one of the most iconic battlefield nuclear weapons, the M65 atomic cannon (you have possibly seen footage or photographs of its testing in 1953). The M65 could fire 280 mm atomic shells to 20 miles or so. The warhead used in the test footage, the W9 warhead, had an explosive yield of 15 kilotons —15,000 tons of TNT equivalent. That is enough explosive power to destroy a medium-sized city, take a chunk out of a major city's downtown area, or damage about 4 square miles anywhere else. As a tactical weapon in the 1950s, the goal would have been to take out Soviet tanks or troop formations, such as those imagined to be streaming through the Fulda Gap in the event of a Soviet invasion of Western Europe.

But 15 kilotons is the same explosive power as the atomic bomb dropped on Hiroshima in 1945 with such devastating effect. The atomic bombings in Japan had been “strategic” attacks aimed mainly at destroying morale and terrorizing the Japanese high command into surrender. What made 15 kilotons a “strategic” yield depended on where it was aimed; in other words, it is only “low” when compared to weapons whose yield was measured in the hundreds or thousands of kilotons. The main technical difference is that the atomic artillery has such limited range that its ability to threaten a city in the Soviet Union would be zero unless you somehow wheeled it right up to it. In contrast, the bomb dropped on Hiroshima fell out of the bay of a long-range airplane.

During the Cold War, the United States and the Soviet Union designed dozens of varieties of tactical nuclear weapons, which they produced in the many tens of thousands. Both sides still retain limited stockpiles of weapons intended to have tactical applications. These weapons range in power from a few hundred tons of TNT upwards to several kilotons. Their intended “tactical” uses included nuclear-tipped anti-aircraft missiles to shoot down Soviet bombers, nuclear-tipped torpedoes meant to take Soviet ships and submarines, and even oddities like nuclear landmines to destroy bridges.

Some of them were very small. The smallest U.S. nuclear weapon ever developed, the W-54, had a minimum yield of “only” 10 tons of TNT equivalent (0.01 kilotons) and could be carried by a single soldier in an (awkwardly large) backpack. Such a weapon was deliberately made as a “bridge” between conventional and nuclear explosives yields. By comparison, the Oklahoma City Bombing in 1995 is commonly cited as having been around 2 tons of TNT equivalent (0.02 kilotons). The largest conventional weapons globally (the U.S. MOAB and the Russian FOAB, both fuel-air bombs) have yields in the range of 10-40 tons of TNT equivalent (0.01–0.04 kilotons).

The U.S. currently deploys two types of “low-yield” weapons. According to Hans Kristensen and Matt Korda of the Federation of American Scientists, it has around 230 B61 gravity bombs deployed for tactical use, including many fielded in Europe as part of the NATO nuclear arsenal. These come in various yields, including as low as 300 tons of TNT. These would need to be dropped out of bombers or fighter planes. The U.S. has also, in recent years, begun deploying a new warhead variant (the W76-2) on U.S. submarine ballistic missiles that are estimated to be around eight kilotons in yield. This was started during the Trump administration, which argued that the U.S. needed a more rapid means of delivering a lower-yield weapon than an airplane. Whether this is a good idea has been hotly debated; those in favor say it will deter Russia from using its low-yield weapons, and those against say it will possibly lower the threshold for nuclear use. It would be impossible for Russia to know it was “low-yield” until it detonated, leading to real dangers of swift escalation.

These categories of strategic and tactical, of low-yield and not, are all, as you can see, a bit leaky. They are the consequence of decades of Cold War-based nuclear strategizing, which sought to create order out of the chaotic possibility of mass destruction and the half-logic, half-terror calculus of nuclear deterrence. But these strategies were based on a fantasy of clairvoyance, of knowing what an enemy might think or do as a response to an action you took. As a RAND game theorist in the 1960s ended an argument with a three-star general on this very subject: “General, I have fought just as many nuclear wars as you have.”

Could Russia strategically or tactically use a “low-yield” nuclear weapon in Ukraine? Russian military doctrine often invokes the concept of “escalate to de-escalate,” the idea that something like a tactical nuclear weapon might be a way to force an enemy to the negotiating table or to capitulate because they would fear continuing down the path to increasing escalation. It is worth noting that none of the arms control treaties that the U.S. and Russia are currently party to regulate the deployment or use of tactical nuclear weapons.

The U.S. and NATO clearly consider this to be something Russia might do and have taken various public (and probably private) measures to signal to Russia that to do so would not be in Russian interests: that there would be harsh consequences above what has already been implemented, that Russia would not get what it might hope for out of such an action, and that the risks of escalation would be very high. Whether Russian leaders find these threats credible or see the world on anywhere near the same terms as the Americans and NATO representatives do, remains to be seen.

During the Obama administration, as Fred Kaplan reports in his book The Bomb: Presidents, Generals, and the Secret History of Nuclear War (Simon & Schuster, 2020), the National Security Council ran an exercise looking at precisely this question: what could, or should, the U.S. response be to Russian use of tactical nuclear weapons against NATO troops? Kaplan’s account paints a complex range of reactions. The military generals immediately started discussing exactly where and how to deploy a nuclear response. Then-Vice President Biden’s national security advisor interjected that it wasn’t clear a nuclear response was the right choice at all: that there would be more value in isolating Russia and avoiding normalizing the use of said weapons.

Many of the advisors of a Cold War vintage, including the general officer then in command of NATO forces, found this an impossible idea to stomach. Anything other than some nuclear response in kind seemed like it would signal a lack of resolve, even if they could not come up with an agreement about what that would look like in practice.

What would such a response look like today? I don’t think anyone knows, even the people who are currently no doubt coming up with contingency plans for just such a situation until the thing happens. It would be uncharted territory, and any decision about using U.S. nuclear forces would sit with the President. Now, as in the Obama administration, his advisors would likely be split on the matter. All outcomes would be risky in different ways, both short and long-term. Let’s hope that the risk and the uncertainty involved keep Russia and its leaders thinking that the most straightforward option — not even starting down this path — is the best one.