The Pentagon confirmed Tuesday that it has deployed the W76-2 low-yield, submarine-launched, ballistic-missile nuclear warhead.

“The U.S. Navy has fielded the W76-2 low-yield submarine-launched ballistic missile (SLBM) warhead,” the Defense Department wrote in a statement posted online.

Hans Kristensen, the Washington-based nuclear analyst at the non-profit Federation of American, reported last week that the Navy deployed “one or two” W76-2 warheads on Trident II D-5 missiles in December. The missiles were carried on an Atlantic patrol by the USS Tennessee (SSBN-734) ballistic-missile submarine, which Kristensen and co-byliner William Arkin said left Naval Submarine Base Kings Bay in Georgia in late 2019.

In the 2018 Nuclear Posture Review, the Trump administration wrote that the U.S. required a low-yield nuclear weapon that could evade air defenses to dissuade an adversary from trying to win a conflict with a limited nuclear strike. The review specifically cited Russia as the potential adversary in this scenario.

The W76-2 is a modified version of the W76-1, which itself is a refurbished version of the smaller of the Navy’s two sub-loaded ballistic-missile warheads. The W76-1 life extension, which wrapped up about a year ago, aimed to keep the weapon in service for another 30 years.

The W76-1 has a roughly 100-kiloton yield, while W76-2 might have a yield of less than 10 kilotons, according to a report from the Congressional Research Service, which cites unspecified unclassified sources.

Opponents of the W76-2 say that: the new weapon unnecessarily duplicates capabilities already approximated by the B61 nuclear gravity bomb and the W80-tipped AGM-86B air-launched cruise missile; that its use would needlessly expose to counterattack the ballistic missile submarines intended to dissuade Russia and other nuclear adversaries from launching a full-scale nuclear-strike on the U.S. homeland; and that limited nuclear war will lead to general nuclear war.