First U.S. Navy Sub Deploys With Tactical Nuclear Weapons

The U.S. Navy is now deploying a low-yield nuclear weapon aboard some of its nuclear ballistic missile submarines. The new five-kiloton weapon could be used for smaller targets than the strategic 100-kiloton or 475-kiloton warheads currently in circulation among the service's 14 SSBNs. 

"The U.S. Navy has fielded the W76-2 low-yield submarine-launched ballistic missile (SLBM) warhead," said John Rood, under secretary of defense for policy, in a statement Tuesday. "This supplemental capability strengthens deterrence and provides the United States a prompt, more survivable low-yield strategic weapon." According to Rood, the advantage of a low-yield weapon is that it shows potential adversaries that the United States has a broad range of options under "any threat scenario" and that there is no advantage in a "limited nuclear employment." 

The W76-2 was first disclosed to the public in the Trump administration's 2018 Nuclear Posture Review (NPR). The NPR describes it as a response to an equivalent Russian capability, and according to the Federation of American Scientists, its development is motivated in part by the perception that Russia might consider a limited low-yield nuclear strike in the event of a conflict in Europe - without fear that the U.S. would respond in kind.

\With a small nuclear weapon on a proven sub-launched ballistic missile, American forces now have the ability to reliably penetrate Russian air defenses and deliver a proportionate response. Unlike cruise missiles and fighter-dropped bombs, the U.S. Navy's Trident II D5 SLBM is a genuine intercontinental delivery platform: it has a standoff distance of at least 4,000 nautical miles, multiple reentry vehicles and a terminal approach speed of about Mach 24, making it exceptionally difficult for an adversary to stop. 

Tactical-sized nuclear weapons have long drawn scrutiny for potentially "lowering the bar" for nuclear arms use: as the potential damage is small relative to a megaton-sized strategic warhead, a kiloton-sized bomb might prove more tempting to actually launch during a conflict. The NPR addressed this criticism, asserting that the new bomb is “not intended to enable, nor does it enable, ‘nuclear war-fighting.’" 

However, the Federation of American Scientists suggests that the delivery vehicle effectively makes the W76-2 unusable except in an attack against a small regional opponent. The low-yield bomb would launch aboard the same ballistic missile used for America's highest-yield strategic weapons, and if deployed in retaliation against Russian forces, it would create a signaling problem. Russia would have a narrow window in which to decide whether an inbound Trident II carried a few very small bombs or up to eight city-size bombs - and whether to begin a full-scale nuclear response.