What are Russia’s nuclear capabilities?

Russian President Vladimir Putin has escalated his war in Ukraine by calling up military reserves, illegally annexing areas of eastern Ukraine, and threatening nuclear war to ­salvage his stalled invasion. Now the world is closer to nuclear conflict than at any time since the Cuban Missile Crisis. What threat does Putin’s nuclear stockpile pose?

How many nuclear weapons does Russia have? The Federation of American Scientists estimates Russia has 5,977 nuclear warheads, including hundreds retired but not yet ­dismantled, in its inventory. The U.S. Defense Intelligence Agency estimated last year that 1,000-2,000 of Russia’s nuclear warheads are on shorter-­range, nonstrategic weapons with relatively low explosive yields, typically 0.3 to 100 kilotons of TNT equivalent. (The largest bombs yield thousands of kilotons.) The United States, by comparison, has 5,428 nuclear warheads in use and retired. Russia and the United States possess 90 percent of the world’s 12,705 warheads.

When were nuclear weapons last used in war? The United States destroyed Hiroshima and Nagasaki, Japan, with two nuclear bombs ranging about 15-20 kilotons in August 1945 to force an end to World War II. Since then, the United States and Russia (formerly the Soviet Union) have relied on nuclear weapons to deter war through the threat of “mutually assured destruction.”

How likely is Russia to use them? Most analysts think it’s unlikely Putin will order a nuclear strike, but Russian plans are intentionally ambiguous. Russia’s policy calls for using nuclear weapons in response to a nuclear attack and in response to conventional weapons that threaten the existence of the state. Foreign Minister Sergey Lavrov said at the United Nations this policy extends to the eastern Ukrainian provinces Russia fraudulently annexed on Sept. 30.

What might Russia target with a nuclear warhead? Putin could ­target critical infrastructure, such as electrical grids or power plants, and military bases or depots. He could also order a detonation over the Black Sea to coerce NATO countries to abandon Ukraine: Russian military strategists have long advocated this tactic—dubbed “escalate to de-escalate”—to shock an adversary into capitulation. A strike on Ukrainian leadership or its citizens to cause widespread destruction is much less likely.

What would the international ­community do? Western condemnations would be swift, but as Ukraine is not a NATO member, countries in the bloc wouldn’t be obligated to respond militarily. U.S. National Security Adviser Jake Sullivan said in late September the U.S. government has “communicated directly, privately to the Russians at very high levels that there will be catastrophic consequences for Russia if they use nuclear weapons in Ukraine.”