What Are B61-12 Gravity Bombs—Russia Says U.S. 'Lowering Nuclear Threshold'

NATO bases in Europe are set to receive upgraded B61-12 air-dropped gravity bombs in December, U.S. officials told NATO allies during a closed-door meeting in Brussels this month.

According to Politico this is months ahead of the original schedule that would have seen the weapons delivered next spring.

Russia reacted by saying that Moscow will take the move into account in its military planning, with Russian Deputy Foreign Minister Alexander Grushko announcing that the decision to accelerate the deployment of the upgraded bomb lowers the "nuclear threshold."

"We cannot ignore the plans to modernize nuclear weapons, those free-fall bombs that are in Europe," Grushko told state RIA news agency.

"The United States is modernizing them, increasing their accuracy and reducing the power of the nuclear charge, that is, they turn these weapons into 'battlefield weapons', thereby reducing the nuclear threshold," Grushko added.

The B61-12 is a modernized version of the B61, a family of thermonuclear gravity bombs that has been part of the U.S. military stockpile since 1968. The upgrading of the gravity bomb has been in the works for many years now, and the project has been described as the most expensive nuclear bomb project ever.

The 12-foot B61-12 bomb carries a 50 kilotons warhead—the equivalent of 50,000 tons of TNT—and is extremely precise, thanks to a controlled tail rudder which also allows for the removal of its parachute. Because of this tool, pilots do not have to fly exactly over targets to drop the bomb.

Military magazine The National Interest has described the B61-12 as "the most dangerous nuclear weapon in America's arsenal" for its versatility rather than for its nuclear yield, which is lower than others. The B83 nuclear bomb, by comparison, has a maximum yield of 1.2 megatons, or 1,200 kilotons.

The combination of accuracy and low-yield that characterizes the B61-12 gravity bomb is what makes it the most usable nuclear bomb in America's arsenal, the magazine said, adding that "accuracy is the most important determinate of a nuclear weapon's lethality."

Pentagon spokesman Brig. Gen. Patrick Ryder told Politico that the accelerated deployment of the B61-12 gravity bomb "is in no way linked to current events in Ukraine and was not sped up in any way," but the move comes at a time of heightened tensions over Russia's nuclear threats, and it brings its own risk of escalating a situation already under strain.

At the moment, the U.S. has some 200 deployed working tactical nuclear weapons, according to Reuters, half of which are deployed in allies' bases in Belgium, Italy, Germany, the Netherlands and Turkey. Russia, on the other hand, is estimated to have around 2,000 such weapons.

According to the Federation of American Scientists (FAS), Russia and the U.S. currently own approximately 90 percent of all nuclear warheads, with each having around 4,000 warheads in their military stockpiles.

Newsweek has contacted the U.S. Department of Defense and Russia's defense ministry for comment.