A low-yield nuclear weapon (sometimes called a "mini-nuke" or, in older doctrine, a tactical nuclear weapon) is a warhead whose explosive force is significantly smaller than that of strategic weapons. While there is no universally fixed threshold, analysts generally place low-yield warheads at or below roughly 20 kilotons — comparable to or smaller than the bombs dropped on Hiroshima (~15 kt) and Nagasaki (~21 kt). Some modern variants are dialable down to a fraction of a kiloton.
The category gained renewed attention with the 2018 U.S. Nuclear Posture Review, which called for a low-yield variant of the submarine-launched Trident D5 missile. This weapon, designated the W76-2, entered deployment on U.S. Ohio-class submarines in early 2020, as confirmed by the Federation of American Scientists and the U.S. Department of Defense.
Proponents argue that low-yield weapons strengthen deterrence by closing a perceived "gap" — discouraging adversaries from using small nuclear weapons under the assumption that the United States would be self-deterred from responding with massive strategic strikes. Russia's so-called "escalate to de-escalate" doctrine is frequently cited in this debate, though scholars dispute whether such a doctrine is formally Russian policy.
Critics, including former Secretary of Defense William Perry, warn that low-yield weapons lower the threshold for nuclear use by making them appear more "usable." Concerns include:
- Discrimination problem: an adversary detecting a launch cannot distinguish a low-yield warhead from a strategic one, risking full retaliation.
- Normalization: blurring the firebreak between conventional and nuclear conflict.
- Arms race pressure: prompting reciprocal developments by Russia, China, and others.
Low-yield weapons exist in the arsenals of multiple nuclear-weapon states. They are not separately limited under New START, which counts deployed strategic warheads regardless of yield, and they fall outside the now-defunct INF Treaty's coverage as well.
Example
In February 2020, the U.S. Department of Defense confirmed that the W76-2 low-yield warhead had been deployed aboard the USS Tennessee, marking the first fielding of a new low-yield U.S. submarine-launched warhead in decades.
Frequently asked questions
There is no formal treaty definition, but analysts commonly use a threshold of about 20 kilotons or less, with some modern designs adjustable down to under one kiloton.
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