We are again living in a potentially nuclear age, where tensions run high and the threat is real.

On Aug. 6, 1945, the city of Hiroshima was obliterated by a single American atomic bomb. I’ve lived with that reality – or perhaps I mean surreality – since my childhood. No one my age (77) is likely to forget the duck-and-cover drills we all performed, diving under our school desks, to prepare for the Soviet Union’s attempted atomic destruction. We followed the advice of the cartoon character Bert the Turtle – in a brief film I remember seeing in our school cafeteria – who “never got hurt because he knew just what we all must do: he ducked and covered.”

That was life in 1950s New York City. On my way to school, I would pass the S-signs for “safe places to go” (as that cartoon put it) or later the yellow-and-black fallout shelter signs (millions of which were produced). I was 18 when, on Oct. 22, 1962, President John F. Kennedy went on national TV to warn us all of a secret, swift buildup of Communist missiles.

I didn’t know then that the U.S. military already had a Single Integrated Operational Plan, or SIOP, to deliver more than 3,200 nuclear weapons to 1,060 targets in the Communist world. That included at least 130 cities which would, if all went according to plan, cease to exist. Official estimates of casualties ran to 285 million dead and 40 million injured. Nor did I know then, in the 1950s, that American officials, at the highest levels, focused on what was known as the “unthinkable.”

Military and civilian policymakers at the time found themselves writing obsessive sci-fi-style scenarios, not for public consumption but for one another, about a possible “global war of annihilation.”

As the Cuban Missile Crisis began, everything for which we had been preparing to duck-and-cover suddenly seemed to loom too large, in a potentially unduckable fashion.

Here I am, decades later. The world didn’t end. I never actually ducked and covered to ward off a nuclear attack in what passed for real life. And though neither superpower actually dismantled its nuclear arsenal when the Cold War ended in 1991, nuclear weapons did seem to retreat into the ether, into Bert the Turtle’s fantasy world – until the Russian invasion of Ukraine.

CIA Director William Burns has publicly suggested that, sometime soon, Vladimir Putin might turn to atomic weaponry. Welcome to the nuclear age, part 2.

The war in Ukraine has already reached mind-boggling levels of brutality and destructiveness. A Russian diplomatic note to Washington warned of “unpredictable consequences” if the Biden administration kept arming the Ukrainians. Meanwhile, the Russians tested a new intercontinental ballistic missile, which Putin said would make its enemies “think twice.”

If I were making all this up, it would be considered the worst-plotted “take two” imaginable. Those humans didn’t learn a damn thing from almost destroying the planet and each other! So, they decided to do the whole damn thing over again.

The “unthinkable”? Start thinking.

TOM ENGELHARDT created and runs the website TomDispatch.com. He is also a co-founder of the American Empire Project.