For Wikipedia info: Low Yield Nukes
The U.S. plan to deploy new low-yield nuclear weapons is aimed at convincing Russia to respect existing agreements on limiting the weapons, Secretary of Defense Mattis says…
There is no precise definition of the “tactical” category, neither considering range nor yield of the nuclear weapon. The yield of tactical nuclear weapons is generally lower than that of strategic nuclear weapons, but larger ones are still very powerful, and some variable-yield warheads serve in both roles, for example the W89 200 kiloton warhead armed both the tactical Sea Lance anti-submarine rocket propelled depth charge and the strategic bomber launched SRAM II stand off missile. Modern tactical nuclear warheads have yields up to the tens of kilotons, or potentially hundreds, several times that of the weapons used in the atomic bombings of Hiroshima and Nagasaki. Specifically on the Korean peninsula with a nuclear armed North Korea facing off against a NPT compliant South Korea there have been calls to request a return of US owned and operated short range low yield nuclear weapons, nomenclatured as tactical by the US military, to provide a local strategic deterrent to the North’s growing domestically produced nuclear arsenal and delivery systems.
Some tactical nuclear weapons have specific features meant to enhance their battlefield characteristics, such as variable yield which allow their explosive power to be varied over a wide range for different situations, or enhanced radiation weapons (the so-called “neutron bombs“) which are meant to maximize ionizing radiation exposure while minimizing blast effects.