This week sees the 80th anniversaries of the only two uses of nuclear weapons in war against human targets. The Hiroshima bomb will be commemorated on Wednesday. The Nagasaki bomb will be marked on Saturday.
These actions, though generally believed to have brought the Second World War to an end, remain highly controversial, not least because of the large number of non-combatant civilians who died of appalling injuries.
American military authorities prevented the publication of some pictures of the aftermath for many years.
Some of the scientists involved in developing the bomb regretted it deeply. Albert Einstein, who had urged President Franklin Roosevelt to embark on the research which led to it, later said this was ‘the one great mistake in my life’.
But whatever we think now about President Harry Truman’s decision to drop two bombs on Japan, such discoveries cannot be undiscovered.
Several countries, including Britain, concluded that the best response was to build their own bombs, so deterring attack by any other nuclear power. This policy has, on the whole, worked.
The 1961 Cuban missile crisis was defused because both Moscow and Washington had the sense to see that a compromise was better than the end of the world. Both backed down.
Since then, most of us have believed that Mutual Assured Destruction (MAD) would deter all but the crazy from taking actions which might lead to the use of nuclear weapons.
The Russians have developed a grim system known as the Dead Hand, which would deliver a shattering nuclear response to an American nuclear strike, even if the Kremlin leadership were all dead in the ruins of an irradiated Moscow.
It was this which former Russian President Dmitri Medvedev was referring to when he recently taunted Donald Trump over his approach to Russia.
And Mr Trump duly rose to the bait, proclaiming that he had ordered two nuclear submarines to be ‘positioned in the appropriate regions’ in response to what he called the Russian’s ‘highly provocative’ comments.
This is probably bluster. Mr Trump’s advisers will have told him that Mr Medvedev is not a significant figure.
And the US Navy always has several of its 12 Ohio-class submarines, equipped with formidably accurate Trident multi-warhead missiles, within striking range of Russia.
Even so, with a war still in Ukraine, it would be unwise to be complacent. MAD may have worked so far but the world is madder than for many years, with Russo-American relations tense, dogged by mutual incomprehension and personally unfriendly.
Mr Trump may be unpredictable and erratic but the root of this problem is Vladimir Putin’s cruel and lawless aggression, made worse by despicable bombing attacks on civilians.
Mr Trump is right that it must stop, and it is Mr Putin who must stop it. If he does not, who knows where it might lead?
Russia has relied too long on its nuclear strength to limit the West’s response.
The West must now deploy the most severe conventional military, diplomatic and economic means to bring Putin to the negotiating table and to obtain a ceasefire
