WHEN the “Fat Man” plutonium bomb exploded over Nagasaki, on the morning of Sunday August 9,1945, it did so directly over the city’s Catholic cathedral, where morning Mass was being said. The cathedral and its celebrants were vaporised. Ironically, the pilot of the B-29 bomber was an Irish Catholic who had his aircraft blessed by a priest before leaving the United States. In the 1950s, the celebrated Japanese playwright (and committed Christian) Tanaka Chikao would write an allegorical drama about survivors of the bombing trying to recover their faith.

One article of faith that never seems to waver is the widespread notion that it is only nuclear deterrence that has kept the peace since 1945 – or, at least, stopped a succession of ideological bogeymen, from Stalinist Russia to nutty North Korea, from interfering with the Western way of life.

Today, both Tories and mainstream Labour vigorously support the replacing of Britain’s ageing Trident submarines with a costly new nuclear deterrent. Whatever crocodile tears are shed this anniversary month for the incinerated, irradiated and microwaved inhabitants of Nagasaki and Hiroshima, the British political establishment thinks nukes are a regrettable necessity.

The first obvious fault in the logic of nuclear deterrence is that its original Cold War template involved only two players – the US and its allies versus the Communist bloc. In that simple scenario, each side might hope to guess the next move of its opponent, thus making it relatively easy to keep conflicts from going nuclear. But we live in a multipolar 21st century, with numerous and mutually antagonistic atomic powers. Ergo, the more players, the more risk of nuclear miscalculation. Just watch a regional nuclear war (India versus Pakistan, Iran versus Saudi Arabia) become a global one.

But that said, the original Cold War deterrence model is wholly bogus. We survived the East-West confrontation of 1947-1991 without a nuclear exchange by sheer good fortune, not by rational calculation. A decade ago I had the chance to make a documentary series about the Cold War military for the US History Channel. I got to interview a number of the direct participants. Their recollections – and dismissal of the deterrence myth – made it obvious the world only survived by accident.

Among the most fascinating of the ex-Cold Warriors I got to interview was Herbert York, a key figure in the US atomic weapons industry under President Eisenhower, and later under Jack Kennedy. I met him at his idyllic waterfront home outside San Diego, which was cantilevered out over the Pacific, with a view of dolphins leaping in the setting sun. Inside, Herb was an angry old man, bitter about the cancer that eventually killed him in 2009 – contracted, ironically, from radiation poisoning.

As a young physicist, York worked on the original Manhattan Project to build the atomic bombs dropped on Hiroshima and Nagasaki. In 1952, aged only 32, he was first head of the federally-funded Lawrence Livermore National Laboratory at the University of California. That sounds suitably academic but the LLNL was and is a centre for designing America’s nuclear weapons. Herb’s first big project involved miniaturising nukes to fit the warheads of the US Navy’s new Polaris subs.

Along the way Herb was involved in some pretty nutty projects, he recalled. These included a nuclear-powered missile that would zoom across the Soviet Union at low level deliberately spewing out clouds of radioactive debris. Being involved in such Dr Strangelove research made York utterly sceptical about the utility of nuclear weapons. For instance, that atomic rocket would have irradiated most of Europe on its way to Moscow. York’s work on such insane weapons convinced him of the need for arms control and a ban on nuclear testing, not better nukes. He articulated these ideas in books such as Race To Oblivion: A Participant’s View Of The Arms Race, and A Physicist’s Odyssey From Hiroshima To Geneva.

York’s great fear was that as nuclear weapons became smaller and more sophisticated, their use would be determined by junior officers – or terrorists. That fatally undermines the concept of mutual deterrence managed by politicians. Which is exactly what happened during the Cuban Missile Crisis in 1962. As a schoolboy, I remember our maths class being abandoned as we waited to hear if Russian cargo boats bound for Cuba would refuse to stop for the US Navy ships blockading Castro’s island.

We now know that on 27 October 1962, Soviet submarine B-59 came within a hairbreadth of firing a nuclear-tipped torpedo after being harassed by US warships. B-52 bombers were already circling the Soviet Union and a nuclear winter would surely have ensued.

Again, had President Kennedy actually ordered the invasion of Cuba the local Russian commander on the island would almost certainly have fired his 12 nuclear weapons – about whose existence the Americans were completely ignorant until after the Iron Curtain fell in 1991. I had the chance to interview Robert McNamara, President Kennedy’s Secretary of Defence during the Cuban Missile Crisis. He was only too willing to admit he and Kennedy were not in command of their forward units, and nuclear war could easily have resulted.

DON’T think the UK gets a clean bill of health. RAF reconnaissance planes flew deep penetrations into the Soviet Union during the 1950s. On one such illegal mission, Flight Commander John Crampton was hit by Soviet flak over Kiev. To this day, the MoD refuses to acknowledge these overflights, which could easily have been mistaken by the Soviets for pre-emptive nuclear strikes.

The UK was also a base for illegal American flights into the Soviet Union. For my Cold War series, we interviewed US Air Force Colonel Hal Austin.

In 1954, he flew his Boeing B-47 from RAF Fairford, in Gloucestershire, deep into Soviet airspace, where he was attacked by six Mig-17s and seriously damaged. Such hair-raising missions were conducted without presidential or British authorisation, but on the orders of General Curtis “Bombs Away” Le May, boss of Strategic Air Command and the man in charge of nuking Japan.

Curtis Le May believed passionately in a first strike against the Soviet Union. Every time American bombers entered Russian airspace, the Soviets worried it might be Le May’s much-desired first nuclear strike. These days, how will the Iranian or North Korean military know that those incoming drones are for taking pictures, and not carrying mini-nukes on a first strike? Equally, if the tables are reversed, how will Western commanders know what’s in the warheads of pilotless planes coming our way? They won’t, of course – which puts the kibosh on deterrence.

And the alternative? For starters, I’d spend the £100 billion earmarked for Son of Trident on something useful, like an anti-missile and anti-drone defensive shield. But in an uncertain world, no amount of weaponry will prevent war. That comes from a determined focus on creating a political and economic architecture for peace, as Herbert York argued. We need more of that, and less emphasis on the chimera of “deterrence”.