"This supplemental capability strengthens deterrence and provides the United States a prompt, more survivable low-yield strategic weapon," John Rood, the undersecretary of defense for policy, said in a statement.
He says the weapon, known as W76-2, lowers the risk of nuclear war.
Critics say low-yield nuclear weapons lower the threshold for using nuclear weapons, increasing the risk of nuclear war. And while W76-2’s strength is classified, experts say it likely has around one-third the power of the atomic bomb dropped on Hiroshima in 1945.
The warhead is the first major addition to the U.S. nuclear arsenal in decides and shows a departure from the Obama administration’s policy of lessening dependence of nukes for deterrence.
Details about where and when the weapon was deployed are classified, Rood said.
The Trump administration aims to dissuade Russia from thinking it could win a war in Europe if the country used its own low-yield weapons first, trying to force the U.S. to either surrender or respond with full-scale nuclear war.
Rep. Adam Smith, D-Wash, said "The administration’s decision to deploy the W76-2 warhead remains a misguided and dangerous one," Reuters reported. "The deployment of this warhead does nothing to make Americans safer."
Bruce Blair, co-founder of Global Zero, an international group advocating for the elimination of nuclear arms, also opposes W76-2 and testified in front of Congress last year.
“We must not delude ourselves into thinking lower-yield nukes are more usable in a conflict,” the former Air Force nuclear weapons officer testified.
“Any use of this sea-based weapon -- either first or second -- will risk stoking the flames of conflict and escalating to all-out nuclear war," Blair said. "A wiser response to an enemy’s use of one or two low-yield nukes would be to refrain from nuclear escalation while unleashing America’s ferocious and decisive conventional juggernaut.”
The Associated Press contributed to this report.