Anti-nuclear campaigners expressed alarm Thursday as the Federation of American Scientists revealed the U.S. has for the first time deployed a "low-yield" nuclear warhead on a submarine that is currently patrolling the Atlantic Ocean.

The USS Tennessee left a port in Georgia last month, and Hans Kristenson of FAS said Wednesday that the submarine is the first U.S. ship to patrol with the W76-2 on board—an occurrence which arms control groups says will make nuclear war more likely.

Tim Wright, treaty coordinator for the International Campaign to Abolish Nuclear Weapons (ICAN), called the news "an alarming development that heightens the risk of nuclear war."

An alarming development that heightens the risk of nuclear war. The United States' new "low-yield" nuclear warheads are still powerful enough to kill many tens of thousands of people. #nuclearban https://t.co/OGtKrVwQUe — Tim Wright (@TimMilesWright) January 30, 2020

The ready availability of the warhead on a military ship could cause a shift in thinking about nuclear weapons, with the government treating a nuclear launch as a way to fight wars rather than as a deterrent, nuclear critics say.

The low-yield Trident nuclear warhead was commissioned in 2018 by President Donald Trump.

The warhead has an explosive yield of five kilotons, about a third of the power of the atomic bomb dropped on Hiroshima, Japan in 1945, which killed 80,000 people instantly and tens of thousands later from radiation exposure.

Compared to the bombings of Hiroshima and Nagasaki at the end of World War II, the effect of the W76-2 "would be very beneficial to a military officer who was going to advise to the president whether we should cross the nuclear threshold," according to Hans Kristensen, director of the Nuclear Information Project at FAS, which learned about the recent deployment from government briefings.

The deployment of the W76-2 came five months after the president exited the Intermediate-Range Nuclear Forces (INF) Treaty, which the U.S. and Russia forged in 1987. The withdrawal from the treaty would "put the world at heightened risk of nuclear weapons use and war," ICAN said at the time.

According to Trump's Nuclear Posture Review (NPR), the U.S. government claims the Trident is a deterrent against Russia.

As Kristensen wrote in Forbes last year, however, the Russian threat may be exaggerated by the Pentagon.

"It seems like a perfect threat-funding-loop sales pitch: Russia is increasing its non-strategic nuclear weapons that it is more prepared to use first, so give us more money to build new nukes," wrote Kristensen. "But...in stark contrast with the NPR claim, I hear there's no significant increase in the total numbers. On the contrary, there has been a significant reduction over the past ten years—the very period the NPR uses as the basis for its threat assessment."

While Russia's nuclear threat level is questionable, Trump has said he may direct the use of nuclear weapons to respond to "significant non-nuclear strategic attacks" on the U.S., its allies, or "infrastructure."

On social media, international anti-nuclear groups expressed alarm over the deployment of the Trident warhead.

"Usable" nukes bring us closer to the threshold of nuclear war. https://t.co/729C0Nviok — Scrap Trident (@ScrapTrident) January 29, 2020

The presence of the warhead on a patrolling submarine "brings us closer to the threshold of nuclear war," tweeted the Scottish anti-nuclear campaign Scrap Trident.