In August 2017, residents in Japan's Hokkaido region were woken by an SMS that informed them to take cover, as a ballistic missile was passing overhead. The North Korean missile passed through Japanese airspace for two minutes, before burying itself at sea 500 miles off the coast.
We don't know much about what contingency plans the UK has in place for such a scenario — and to be fair, we're not exactly neighbours with North Korea — but with Kim Jong Un's nuclear masquerading making headline news, fears have been raised about the regime's ability to strike targets farther afield. It's a highly unlikely prospect, of course — and we're musing here, rather than scaremongering — but what would happen if London were hit by a rogue nuclear bomb?
Naturally, some clever clogs has thrown together a way for us to find out. Nuclear historian Alex Willerstein is the creator of the website NUKEMAP, which allows the overly-curious to explore the effects of a hypothetical nuclear bomb placed at any given location around the world. The site gives a visual representation of what areas would be worst affected, and even gives an estimate of the death toll.
North Korea's thermonuclear test in August of 2017 — which took place under a mountain at the Punggye-ri test site — is estimated to have had a yield of 150kt. To put that into perspective, the blast was so powerful that it triggered a 6.3-magnitude earthquake in the region. So what does it look like if we use the NUKEMAP site to centre the device on Westminster?
The results certainly don't look pretty. The site estimates that there would be 334,290 casualties as a result of the blast, along with 1,088,503 injuries. Keep in mind that this is just an estimate: the results don't take into account the effects of nuclear fallout, nor the fact that the city is more heavily populated at certain times of day.
The innermost orange circle, and unquestionably the most severe, is the fireball radius (450m). Within this area, a nuclear fireball would obliterate the Houses of Parliament, Westminster Abbey and a decent chunk of Whitehall. There would be no survivors. The effects lessen as we move further away from the centre of the blast, but they are by no means any less shocking. The green ring (radiation radius, 1km), represents the area within which we can expect a 50-90% mortality rate, and the blue ring (air blast radius, 3.74km) represents the area within which the resulting pressure would cause most residential buildings to collapse, with widespread fatalities. The outermost ring (thermal radiation radius, 5.26km), some distance from the blast, would still result in third degree burns to any within, causing severe scarring and disablement — and in many cases, may require amputation.
Naturally, an attack on home soil would evoke a political response. The UK's nuclear command chain dictates that if the sitting prime minister were to authorise a retaliatory nuclear strike, the order will go to the person below the prime minister on a dual-track basis (meaning two persons are required to authenticate at each stage of the process), until it eventually reaches our nuclear submarine fleet. The fleet will carry out a strike on the coordinates given, though they will not necessarily know what the target is.
But as we saw in the example given above, a strike that completely wiped out Westminster — and therefore possibly the prime minister — means that there would have to be an alternative means of response. To cover for such an eventuality, every prime minister will have written a letter of last resort upon taking office, seen by their eyes only, and stored securely within the safes of each of the UK's four nuclear submarines. The letter instructs the submarine commander of what action to take should Her Majesty's Government be completely wiped out. Before following through with the orders, the commander will have to assess whether the government has fallen, by trying to make contact with Naval Command and — infamously — checking if BBC Radio 4 is still broadcasting. The aforementioned letters are destroyed unopened whenever a new prime minister takes office, and while nobody knows for sure what options have been tabled, there are thought to be four key responses: launch a retaliatory nuclear strike, don't launch a retaliatory nuclear strike, allow the commander to use their own judgement, or offer the fleet to the US or Australian Navy.
It's safe to say, then, that a nuclear attack from North Korea would have devastating consequences — whether London was the target or not. But do we have anything to worry about?
Though devastating, the latest North Korean test pales in comparison to the largest nuclear bomb the US has ever tested. If detonated over Pyongyang, the 15mt device would result in 3,261,930 fatalities and 2,900,200 injuries. The doctrine of mutually assured destruction — a form of Nash-equilibrium, where neither side has incentive to launch an attack — ensures that any attack stemming from North Korea would be met by an equally, if not more devastating retaliatory missile, effectively ending the regime. Thus, most experts agree that North Korea's military bravado is, well, just that — designed to stem the threat of a foreign attack, not to actively encourage it.
After all, the last thing anyone wants — not least Kim Jong Un — is an all-out nuclear war.