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''Of course, the whole point of a Doomsday Machine is lost if you keep it a secret,'' said Dr Strangelove to the Soviet ambassador in Stanley Kubrick's classic film of the same name.
Fifty years later, it would appear the Russians have finally watched the movie.
In Kubrick's film, a rogue American air force commander orders a nuclear strike on the Soviet Union - but he doesn't know the Russians have built a Doomsday Machine that will automatically explode and spread lethal radioactive contamination all over the world if American nuclear weapons land on the USSR.
So everybody dies.
Moscow doesn't want the United States to make the same mistake in real life, so it has just let us know it is building a mini-doomsday machine.
It wouldn't destroy the whole world, just a half a continent or thereabouts like, say, all of the United States east of the Mississippi River, or all of China within 1500km of the coast.
It is awkward to say this sort of thing through diplomatic channels - ''I have the honour to inform Your Excellency that we can now destroy half of your country with only one explosion'' - so the preferred method is to get the word out by an accidental ''leak''.
In this case, the leak occurred on November 10 in the Black Sea resort of Sochi, where President Vladimir Putin was meeting his senior military officers.
A cameraman for state-owned Channel One television ''accidentally'' filmed a general studying a poster of a new weapon called ''Status-6'', a giant torpedo (a ''robotic mini-submarine'', the poster called it) that can travel up to 10,000km at high speed carrying a huge payload - like, for example, a truly gigantic thermonuclear weapon.
And the film clip was broadcast all over Russia before the ''mistake'' was discovered.
The text on the poster was clearly legible.
The ''oceanic multi-purpose Status-6 system,'' it said, is designed to ''destroy important economic installations of the enemy in coastal areas and cause guaranteed devastating damage to the country's territory by creating wide areas of radioactive contamination, rendering them unusable for military, economic or other activity for a long time''.
''It's true some secret data got into the shot. Therefore it was subsequently deleted,'' President Putin's spokesman, Dmitry Peskov said.
But the complete text and a cutaway diagram of the Status-6 are now available on a hundred websites, and the Kremlin doesn't seem particularly upset.
Indeed, the government newspaper Rossiiskaya Gazeta later reported details of the weapon, without showing the diagram, and speculated it would carry a gigantic cobalt bomb, just like the Doomsday Machine in Dr Strangelove, although a little smaller.
The explosive core of the warhead would be a massive thermonuclear bomb - perhaps as big as 100 megatons, almost twice as big as any bomb ever tested.
Around this core would be wrapped a thick layer of cobalt-59, which on detonation would be transmuted into highly radioactive cobalt-60 with a half-life longer than five years.
''Everything living will be killed,'' the paper said.
Konstantin Sivkov, of the Russian Geopolitical Academy, helpfully explained to the BBC Russian Service a warhead of up to 100 megatons would produce a tsunami up to 500m high, which together with the intense radiation would wipe out all living things up to 1500km deep inside US territory.
This is crazy talk, but the Russians have always lived in fear the United States might somehow develop the ability to destroy Russia without suffering serious retaliation. And the truth is that the American military have never stopped looking for some way to do exactly that.
Back in the 1950s, when US Strategic Air Command really could have destroyed the Soviet Union with impunity, physicist Andrei Sakharov (later the winner of the Nobel Peace Prize) actually proposed a weapon rather like System-6 so Russia could take revenge from the grave.
The latest US gambit is anti-ballistic missile (ABM) defences to be based in Eastern Europe, allegedly to defend against nuclear missiles coming from Iran.
But Iran doesn't have any nuclear weapons, and it may never get them.
Yet the American ABM system is going to be deployed in Poland and Romania soon.
Moscow is therefore convinced the whole project is really intended to shoot down its own missiles shortly after launch.
There is no realistic possibility the American ABM defences could really destroy all or even most of Russia's missiles, but that is exactly what Mr Putin is saying to his generals on the sound-track just before the TV clip focuses on System-6.
System-6 is not scheduled to be operational until 2019-20, and it may never be built at all.
But the old game of nuclear one-upmanship goes on even though the two countries are no longer really enemies.
It is pointless and potentially very dangerous, and President Obama might usefully spend the last of his political capital putting an end to it.
• Gwynne Dyer is an independent London journalist.