Armageddon was always difficult to imagine, even with the holocaust of Hiroshima to prompt us. It took the unsentimental, contemporary accounts from Japan by the American writer, John Hersey, to provide a glimpse of what takes place when nearly 100,000 people die on a single day. He described two priests walking through Hiroshima. "They did not know where they were; the change was too sudden, from a busy city of 245,000 that morning to a mere pattern of residue in the afternoon. They encountered only one person, a woman, who said to them as they passed, 'My husband is in those ashes.'"
Hersey went on to describe a gathering of survivors in a grove of bamboos, pines, laurel and maples that had escaped the fire. "The hurt ones were quiet; no one wept, much less screamed in pain; no one complained; none of the many who died did so noisily; not even the children cried; very few people even spoke. And when Father Kliensorge gave water to some whose faces had been almost blotted out by flash burns, they took their share and then raised themselves a little and bowed to him, in thanks."
Since the end of the Cold War, it has become more difficult to envisage such mass destruction: we rely upon a vaguely reasoned sense of comfort that the collapse of US-Soviet tension has pushed the clock back from the last few minutes before midnight. Nuclear war, which seemed so imminent during the 1962 Cuban missile crisis, is no longer a talking point or a central icon of political protest. We sup full of other horrors, in Bosnia, Rwanda, Cambodia, but The Bomb has become almost a myth, a nightmare from which we have, perhaps, awoken.
But it has not gone away. Britain retains its nuclear arsenal. Atomic weaponry is no longer confined to the major powers. India has the bomb, so does Israel. South Africa, under Nelson Mandela, is alone in having given up its capacity. In the last year, North Korea generated a wave of tension over its cat-and-mouse game with international nuclear inspectors.
The language of the defence expert in this nuclear arena has always possessed a haunting strangeness.
Probably Mutually Assured Destruction best captures the theory of a stable nuclear stand-off. Historians have also mostly argued that the bombing of Hiroshima and Nagasaki brought the war against Japan to a swift conclusion and so saved many lives among the allied forces, thus offering a ready moral case for the bombing. Yet, it is now argued that Japan was, in fact, already preparing to surrender. The entry of the Soviet Union into the war in the Far East in 1945 may have been more influential in the capitulation than what amounted to just the firebombing of two more Japanese provincial cities. But we should also perhaps ask whether the Balance of Terror of the nuclear age would have been less stable, less reliable without the collective memory of Hiroshima and Nagasaki.
Certainly this half century of nuclear balance has coincided with an absence of direct conflict between the world's two largest powers, the United States and the Soviet Union. Measured against the behaviour of the old European imperial powers - France, Germany and Britain - in the pre-nuclear age, that is a remarkable enough fact.
It would manifestly be a mistake to take this stability for granted. The post-Cold-War world may well turn out to be less stable and more violent than its predecessor. Yet, today, we barely discuss the meaning of atomic weapons in this new era. Partly because senior Labour Party figures no longer flirt with CND - though many have past associations with the movement - the debate about Trident becomes one chiefly about resources. There is a need to ask again some of the basic questions of nuclear warfare: does Trident make Britain safer from foreign aggression than Belgium or Switzerland? Against whom do we think we would ever use these weapons?
There are many arguments for keeping them. As the United States disengages from Europe, it may be that the French and British stockpile will come to constitute a European deterrent, balanced against a still formidable Russian firepower. Perhaps they will be needed to deter some other, as yet unknown, enemy. How would we feel, for example, if we had given up Trident and French missiles, only to find a hostile regime installed in Algeria or a north African state with warheads aimed at Paris or London? Or is the British and French determination to remain part of the nuclear club no more than an anachronistic way of buying a place at the top table of international institutions like the UN? Is it just one more way in which we fool ourselves about Britain's real place in the world?
It is not that we should again wish to become obsessed, as earlier generations did, with the nuclear threat. Against the risks of nuclear conflagration, it is right to set the 30 million people who starved during China's Great Leap Forward and Cultural Revolution, and the many other cataclysms which we are called upon to combat. But when feet are dragged on the way to a comprehensive test ban, or on the next stage of resisting nuclear proliferation, or on the pointless testing of the latest French technology in the South Pacific, we need to remind ourselves of the risks to which our planet is exposed and to continue the search for international political structures to contain them.
John Hersey described the whirlwind produced by the Hiroshima blaze, huge trees crashing down, small ones uprooted. He told how a man put a piece of cloth over a friend's eyes "so that the feeble man would not think he was going crazy." Still crazy after all these years, the blaze of Hiroshima sheds a light which has to be faced.