The U.S. has around 500 B-61 low-yield, or “tactical” nuclear gravity bombs ― some with yields as small as 0.3 kilotons in their arsenal, said James McKeon, a nuclear weapons analyst for the Center for Arms Control and Non-Proliferation.
However, it’s not the size that determines their tactical or strategic status, McKeon said. The bombs are tactical ― and not governed by the 2010 new Strategic Arms Reduction Treaty, or START treaty ― if they are delivered on a tactical aircraft, such as an F-16 or F-15 fighter jet, McKeon said.
The weapons become strategic if delivered via on of the nation’s strategic assets, such as the B-2 or B-52 nuclear-capable bombers.
via Defense News Mattis: Use of tactical nuclear weapons discussed with South Korea