What are tactical nuclear weapons and why did Russia order drills?

Russia's Defense Ministry said Monday that the military would hold drills involving tactical nuclear weapons — the first time such an exercise has been publicly announced by Moscow.

A look at tactical nuclear weapons and the part they play in the Kremlin's political messaging.

Unlike nuclear-tipped intercontinental ballistic missiles that can destroy entire cities, tactical nuclear weapons for use against troops on the battlefield are less powerful and can have a yield as small as about 1 kiloton. The U.S. bomb dropped on Hiroshima during World War II was 15 kilotons.