That was too close… Five accidental nuclear detonations that never were

Updated: Mar 1, 2019

By Andy Cooke

This series will look at the inverse of the “For Want of a Nail” idea: times when the last nail just about held. Times when, if it hadn’t done so, history would very probably have taken a markedly different course.


First up: nuclear weapons


Nuclear weapons are heavily safeguarded.


They are designed to be failsafe.


Unless explicitly armed and triggered, they will not go off.


The above sentences are true. Today. They haven't always been.


Through the late Forties and Fifties, and even into the Sixties, nuclear weapons were far less safe than we believed. It’s almost miraculous that we didn’t have an accidental detonation in that time. Even though, in two of my example, the accidental detonations would only have been a little bit earlier than the deliberate ones that did occur, the consequences of the change would have changed history.


I've chosen five, based on my subjective view of their ability to have changed history:



5: Trinity – premature explosion – did NOT happen July 15th 1945.


The Manhattan Project scientists spent a long time working out how to detonate an "implosion" bomb - which would be far more efficient than the clumsier (and potentially more dangerous to use) "gun-type" bombs that were the alternative. The latter type would only ever be used once - Little Boy, dropped on Hiroshima.


The first ever nuclear bomb, to be tested at Trinity, was of the implosion type. Named “The Gadget”, it was to be set off by a perfectly symmetric shock wave from the explosive trigger. Thirty-two shaped charges had to be set off exactly simultaneously for this to work. A new electrical detonator system was invented to do this, using a bank of capacitors called an "X-unit". In practice, these were sometimes... unpredictable. A week before the Trinity test, a lightning storm in the area caused an X-unit to fire due to the static electricity in the air. Had it been installed as the detonator of a nuclear bomb, the bomb would have gone off.


In the Trinity test, “The Gadget” was lifted to the top of a hundred-foot wooden tower (with fifteen feet of mattresses piled underneath in case the cable broke). And then, during the night before the test, bad news: a violent electrical storm swept in. After considering the danger, a decision was made: A young scientist was detailed to “babysit” the bomb. What, precisely, he'd be able to do to stop the danger, was unclear. In the end, he simply sat nervously next to it as he watched the lightning bolts and recalled seeing an X-unit triggered by static electricity in a similar situation.


As it happened, this particular X-unit did not fire prematurely, and the Gadget later detonated exactly as planned (without a nervous scientist sitting near it), on July 16th. Otherwise we’d be in a world where the first nuclear bomb test resulted in a premature detonation and the vaporisation of one of the scientists - one where the possibility of random detonation was seriously questioned from the very start.



4: Little Boy – detonation on aircraft accident – did NOT happen 6th August 1945.

The B-29 bomber, such as that to be used to carry the nuclear weapons, had a high accident rate. The night before the bombing of Nagasaki, two B-29 bombers crashed and burned on the runway at Tinian trying to take off. This, understandably, raised questions of what would happen if the bomber carrying one of the nuclear bombs were to crash.


The first nuclear weapons were not designed to avoid detonation – they were more worried about making them go off at all. As described above, there were two designs: the gun-type (Little Boy - for Hiroshima) and the implosion type (Fat Man - later dropped on Nagasaki). The implosion type could be accidentally detonated by a fire, a bullet striking a high explosive "lens", possibly by sudden impact, so, should there be a problem on take-off, pilots were advised to try to jettison the bomb into shallow water from a low height... and hope for the best.


For the gun-type bomb, like the Hiroshima bomb, this was decidedly NOT advised. As water is a neutron moderator, a possible alternate way to detonate Little Boy would be to introduce water into the bomb. A chain reaction would then occur. So you really did not want to get it wet.


Instead, the aircrew of Enola Gay were given the following advice: if something goes wrong with your aircraft, don’t jettison the bomb. See if you can send someone to crawl over it and pull out the charges (while having trouble on take-off?), and make absolutely sure to crash on land. Their thoughts when they looked at the map of the Pacific between Tinian island and Japan, with the hundreds upon hundreds of miles of water, are not recorded...


Had the Enola Gay had problems on take-off, we could be in a world where the first attempted dropping of a nuclear weapon in anger resulted in the total destruction of the aircraft and airbase from which it took off.


3: The USAF nuking East Anglia – various times, late Forties.


This is more a category of possible alternate worlds. You see, the Mark 3 nuclear implosion bomb was most certainly not failsafe. To the degree that it was considered too dangerous to fly it over American soil with the core and detonators in. The USAF insisted it had to be flown only partially assembled, with final assembly carried out in the air before dropping it.


Unless you were over British soil, however. In that case, the USAF were fine with the bombs being fully assembled, core and all. This meant that B-29 bombers taking off from RAF Lakenheath and RAF Sculthorpe would have the weapons fully intact and ready to go before the aircraft taxied.


Given the USAF’s penchant for insisting on training with live weapons (see #2 and #1 below), it’s very easy to see us heading into an alternate history where the USAF accidentally nuked Norwich soon after the end of World War II

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2: Aircraft fire with Mark 36 hydrogen bomb, Morocco – did NOT explode, 31st January 1958.

A fusion bomb (aka thermonuclear bomb, or hydrogen bomb) is in a different league from the nuclear weapons discussed above. In effect, these are weapons so potent that plutonium (or uranium) nuclear bombs act merely as the trigger for a far greater explosion - one as much greater than a conventional nuclear bomb as the latter is beyond that of a high explosive.


The Mark 36 hydrogen bomb was an early, heavy thermonuclear fusion device, with a yield of between 6 and 19 megatons – up to a thousand times greater than the Hiroshima bomb. One such was on board a B-47, fully armed and live, with nuclear core installed, on the 31st of January 1958.


This aircraft was carrying out runway taxi tests when a rear tyre blew. This caused a small fire on board the aircraft, which rapidly spread. The crew evacuated and the aircraft, now an inferno, split in two. Firefighters desperately hosed water onto the weapon as all other airmen and families were frantically evacuated from the airbase, racing into the desert in the forlorn hope of outracing the explosion's effects.


The heat and flames were beyond the capability of any housing to withstand. Inevitably, the high explosives of the weapon's trigger caught fire.


Somehow, though, they only burned. They didn't detonate.


If they had detonated, an enormous mushroom cloud would have risen over Morocco at the height of the Cold War - if it was at the top end of the Mark 36 yield, it would have been number six on the list of most powerful nuclear explosions ever, out of well over 2,000 detonated in testing.


A thousand times more powerful than the Hiroshima explosion, detonated by accident, in an allied country. That could have made history turn out very differently.



1: The hydrogen bomb dropped on North Carolina and DIDN’T (quite) explode, 23rd January 1961.

A B-52 on an air-to-air refuelling exercise on 23rd January 1961 suffered a fuel leak from the wing. It happened to be carrying two Mark 39 thermonuclear bombs, each with a yield of nearly 4 megatonnes.


Emergency procedures to dump the fuel followed - but these failed. The aircraft now had one wing full of fuel and the other empty. Unbalanced, it went into an uncontrollable spin. The crew were ordered to bail out, five of the eight doing so successfully (sadly, the other three died). The aircraft broke up in mid-air, the centrifugal forces pulling the bomb-release lanyard in the cockpit, and the two bombs fell towards the ground near the town of Goldsboro.


On one of them, the arming wires pulled out, the pulse generator activated, the barometric switches closed, the arming sequence ran through, and, on impact, the fuse sent the firing signal.


But there was still one – just one – arming device left. The ready/safe switch in the cockpit had been set to SAFE.


There had been times on other aircraft when the ready/safe circuit was sometimes glitchy and armed the bombs on board, anyway, despite being set to safe. Fortunately, that particular glitch hadn’t happened here, otherwise we’d be in a world where the Sixties opened with the USAF nuking their own country with a hydrogen bomb 250 times as powerful as the Hiroshima bomb.


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