A ship exploding with the power of a nuke sounds far-fetched. But it could happen

In fact it’s surprising just how large the scope for maritime disasters is

There is a ship, the Motor Vessel Ruby, currently at anchor 15 nautical miles off Margate in Kent with a cargo of 20,000 tons of ammonium nitrate. This is the same material that caused the devastating Beirut explosion in 2020 but seven times the amount. Were it to explode, the yield would be in the region of that produced by 5 kilotons of TNT. Tactical nuclear weapons today range from 0.5 to 10 kilotons. The bomb which hit Hiroshima in 1945 was 15 kilotons. 
Add to this that the Ruby sailed from the Russian port of Kandalaksha near Murmansk, ran aground, damaged its rudder, cracked its hull and has been bounced from pillar to post since, and you can see why people are interested. It’s certainly to be hoped that the Ruby’s fuel tanks are undamaged: a mixture of ammonium nitrate and fuel oil, ANFO, explodes much more easily than the nitrate alone and is used for blasting in the mining industry – and also in terrorist truck bombs.
There are three parts to this discussion – the shipping of hazardous cargoes, Ruby’s movements and the possible weaponising of commercial shipping. I find all of these interesting so I will cover them all, but the point of the article is the last one. Ruby isn’t an attack, but what if it was?
In terms of moving hazardous cargo, what Ruby was doing is not that unusual. Ships move approximately 50 million tons of ammonium nitrate around the world a year in vessels specifically designed to safely manage it. Likewise, there are many other ships moving many millions of tons of other hazardous cargoes around so that we can go about our lives. Nothing at sea is ever risk-free but thinking of the Ruby as a highly volatile bomb ready to go off at any moment is overly alarmist. 
Even her movements, whilst erratic, are not that unusual. A vessel registered in Malta, owned by “interests in Syria” but operating under a time charter to a company based in UAE all sounds a bit vague, and it is, but again that’s not unusual in shipping. Ruby first entered Norwegian waters at the end of August, claiming the need to shelter from a storm, and ended up alongside in Tromso. Hearing that the ship might have been damaged in said storm, Tromso port authorities inspected it and found a crack in the hull, damage to the prop and rudder, a lapsed seafarers’ employment agreement and pollution concerns over the quality of the fuel they were using. 
If this sounds unusual, again, it isn’t. It’s part of international shipping and things like this occur surprisingly often, we just never hear about them. Nevertheless, given the quantity of the cargo, Ruby was ordered to sail from Tromso and anchor out at sea. 
A shipyard in Lithuania then won a tender to make the repairs, but authorities there, on learning of the cargo, refused entry. By now the coverage is picking up despite Norwegian Maritime Authority director Dag Inge Aarhus stating “The ship as it is now… there’s no greater danger [of explosion] than when it’s in an ordinary condition.” 
So homeless the Ruby remained for the next few weeks, heading down the west coast of Norway with a tug in attendance, taking a tow from said tug for a period when she developed ‘engine difficulties’ before going to anchor off the SE coast of England waiting for good weather to refuel before passing through the Channel. This is clearly not a well ship, but again, not a massive outlier either.
By now, lots of agencies are involved including the UK coastguard, the vessel’s insurer, the West of England P&I Club and the UK Secretary of State’s Representative for Maritime Salvage and Intervention (SOSREP) and so on. Notices to Mariners have been issued advising of her position and a safe distance to pass. 
What happens next will be interesting. In risk terms, this is a ‘low likelihood of occurrence’ vs ‘very high severity’ if it does, meaning most ports, including Malta where Ruby now says she is heading, will not accept her. There is a problem, but one that needs calm ship management agents to resolve.
To my mind though, having a bomb this size anchored off the UK raises another spectre which should also be addressed, even if it is nothing to do with the current situation. 
The Ruby signalled her issues many times over a period of weeks – a sure sign that she has no evil intentions. But what if a similar ship was on routine passage, headed for the Channel, then without warning turned into the Thames and increased to full ahead? How quickly would this transition from a routine shipping transit seen hundreds of times a day to a Home Office and Ministry of Defence critical threat and then how quickly could a response happen? 
There is in fact a large organisation devoted to Maritime Counter Terrorism (MCT) which remains at short notice to deal with just this type of problem. It includes the current MCT Squadron of the Special Boat Service (SBS) at Poole and supporting elements including EOD (bomb disposal) teams, some from the Army and another – Alpha Squadron – made up of Navy divers, plus helicopters and other transport options.
Let’s say it happens in the middle of the night and it takes an hour for the relevant authorities to recognise the deviation for what it is, alert the Minister(s) and for the subsequent message to activate the MCT organisation. They are at an hour’s notice to move. It then takes about an hour to get to the Eastern reaches of the Thames by helicopter no matter how special you are. The good news is that in three hours, a ship departing the traffic scheme and heading west at 20 knots still isn’t making it to the Isle of Grain before the SBS are on board and inviting them to rethink. 
That’s good, because the Isle of Grain is home to the largest Liquefied Natural Gas (LNG) terminal in Europe, providing 20 per cent of the UK’s gas supply. If it blew up, we would have a serious energy supply problem.
It could always be worse, though: we could be in Boston, Massachusetts. The Everett LNG facility is responsible for all gas imported into New England and is right in the middle of the city: if that blew up there would be more problems than just gas supply. Proximity between ships, hazardous cargo and population centres is not uncommon and mostly happens without any of us even knowing. 
Back with the case of a ship like the Ruby going rogue and heading up the Thames, the numbers of speed, time and distance mean that we are not talking about a St Nazaire scenario – no one is ramming the Thames Barrier or Tower Bridge. But even if a ship blew up with multi-kiloton force in the eastern reaches, the damage and environmental fallout would be huge. And you can easily translate this scenario to ports in the UK with shorter entries which are much further away from Poole. 
I’m not trying to be alarmist but to register that in an increasingly unstable world, and with adversaries constantly innovating and looking for grey-zone advantages, shipping as a weapon should be taken seriously. 
This risk isn’t new: the UK’s MCT organisation has been around for decades. It was activated in 2001 when the MV Nisha was seized in the Channel en route to the Tate & Lyle sugar refinery at Silvertown in east London. It turned out however that the intelligence which triggered the operation was faulty: the Nisha was not loaded with explosives, just 26,000 tons of sugar. In 2020, MCT teams seized the MV Nave Andromeda, which had been hijacked by stowaways: again, no explosives were found.
That said, in the case of the Thames, enterprising attackers might not need to bring any explosives. Just east of the Isle of Grain with its LNG terminal lies the wreck of the SS Richard Montgomery, which grounded there in 1944 and sank with a cargo of explosive munitions – 1,400 tons of which are still aboard. The vessel’s masts are visible above the water.
You don’t even need explosives to cause a lot of damage with a ship. Back in March the MV Dali suffered a loss of steering at an inopportune moment, wrecking the Baltimore bridge and causing fatalities followed by weeks of disruption in this key port. Sub-optimal port processes and poor engineering standards onboard combined with a big dose of bad luck to flip the situation from ‘routine’ to ‘disaster’ in the blink of an eye. 
The list goes on. Low rainfall restricted the Panama Canal for over a year. A single vessel getting routine ship-handling wrong in high winds closed the Suez Canal for months. The Houthis have seriously restricted shipments via the Red Sea. Shipping makes the world work but it is a point of vulnerability in our civilisation.
To me this is the lesson of the Ruby – shipping is routine until it isn’t. The solution to this constant state of low probability but high risk lies in our intelligence, constabulary and military resources being on constant high alert to respond to problems, whether caused by happenstance or enemy action. And with the latter becoming more likely, anything resembling a resource gap in any of these agencies should be plugged.
“Why we need more fast patrol boats to prevent the equivalent of a tactical nuke going off in the Thames” will probably not be a chapter heading when the ongoing Strategic Defence Review is published, but perhaps it should be.