Since the invasion of Ukraine by Russian forces, there has been speculation about whether Russia would use "tactical nuclear weapons" against their neighbor.

But what exactly are tactical nuclear weapons, and how are they different from "strategic" nuclear weapons, and those deployed on Hiroshima and Nagasaki during World War II?

What are strategic nuclear weapons?

Strategic nuclear weapons are likely the type you are most familiar with, if not by name. They include the "Fat Man" and "Little Boy" dropped on Nagasaki and Hiroshima. 

Strategic nuclear weapons are designed to be dropped on strategic targets. Generally much larger in yield than tactical nuclear weapons, strategic nuclear devices are designed to be used far from battlefields, away from any potential damage to the launching state's civilians and military.

Definitions vary from power to power, but the term "strategic nuclear weapons" generally refers to nuclear devices that can be launched over a high or intercontinental range.

They can cause enormous and indiscriminate damage to large areas, although smaller devices (used e.g. to take out an enemy missile silo) launched over a long range could be classed as strategic nuclear weapons.

What are tactical nuclear weapons?

Tactical nuclear weapons (aka non-strategic nuclear weapons) make up around 30-40 percent of the American and Russian nuclear arsenals, and close to 100 percent of stores in various other countries. They are designed for shorter-range use than strategic nuclear weapons, including weapons that can be launched from air, sea, and ground. 

As with strategic nuclear weapons, the definition differs from country to country, with some (e.g. France, who considers all their arsenal to be strategic) defining shorter-range weapons as strategic rather than tactical. They are generally, however, smaller than strategic nuclear weapons in terms of payload, and are designed to be used for smaller strikes, or attacks on battlefields.

Given their short range, they are not intended to cause widespread nuclear fallout or destruction, either for tactical purposes or in order not to cause damage to the launcher's own side. They can come in the form of short-range missiles, land mines, artillery shells, depth charges, and torpedoes.

There have been agreements limiting the power and size of tactical nuclear arsenals of Russia and the US, but the weapons are not as regulated as their larger counterparts. Though smaller in their devastation, they are not without their own risk (being, as they are, nuclear bombs), not least of which is the chance of escalation should they be used on a battlefield.

"In some respects, [tactical nuclear weapons] are more dangerous than strategic weapons," Senior Fellow at The James Martin Center for Nonproliferation Studies Nikolai Sokov wrote in a piece for Nuclear Threat Initiative.

"Their small size, vulnerability to theft, and perceived usability make the existence of TNWs in national arsenals a risk to global security. And the new perception of the usability of nuclear weapons in both Russia and the United States, albeit for different reasons, could create a dangerous precedent for other countries," Sokov explained.