How an explosive-filled shipwreck in the Thames could trigger a tsunami

Yahoo

14-07-2025

It's a sultry June day on the glistening Thames Estuary; perfect for a river cruise and a spot of lunch in Kent. Yet there's something vaguely unsettling in the distance as we embark the 'Cruiser' tourist boat at the end of Southend pier; gentle waves are lapping at three masts of a wrecked ship, a phalanx of buoys warning people off coming too close.
This wreck is the famous SS Richard Montgomery, an American 'Liberty' cargo ship which was bound for Cherbourg in 1944 and loaded with munitions to support the war effort after the Normandy invasion. But during a gale her anchor dragged into Sheerness' middle sandbank, cracking the hull and buckling under the weight of the cargo. And, despite multiple salvage efforts, it's remained there ever since, the three visible masts acting as an eerie gravestone at its final resting place.
And in so doing – without actually exploding – the SS Montgomery has become something of a cause célèbre. It's also become one of the most monitored wreck sites in the world; there's CCTV and radar making sure no-one breaches the exclusion zone, and aircraft can't fly within 13,100 feet of it.
Perhaps, though, that's not completely surprising when our Captain Richard Bain is merrily telling passengers who have joined today's jaunt that 'over 1,500 tonnes of ammunition are thought to still remain on board', as we set a course from Southend through the treacherous sandbanks that claimed the Montgomery 80 years ago.
'Some say that if it was to detonate today,' he continues, 'there's enough explosive power on this ship to send a five-metre wall of water up the River Thames towards London.'
The 'some say' isn't anecdotal or the stuff of local legend. According to SS Montgomery expert Professor David Alexander, The Royal Military College of Science worked out that the absolute worst case scenario, if the Montgomery was to blow, was a 3,000 metre-high column of water, debris, sand… and that five metre-high tsunami.
Somewhat incredibly, that calculation was in itself made 55 years ago. There has been a lot of procrastination – some might call it governmental gambling – about what to do with the SS Montgomery ever since.
And a lot of reports.
At this time of year, every year, the Maritime and Coastguard Agency – as part of the Department for Transport – publish a survey on the state of the wreck. There are always changes and deteriorations in its state (this year the 'drastic change of the sediment levels in hold 2' and a tilt of the wreck to the east were most notable), although the water is so muddy and the tides so changeable, divers no longer examine it; the work is completed by multibeam sonar technology.
The concern from some, then, is that eventually there will be a catastrophic structural event that will set off a chain reaction of explosions. That event could be as simple as the masts we see hoving into uncomfortably close view collapsing through the deck and compressing the bombs beneath.
What would happen then?
'Doors and windows would be blown from their hinges in both Southend and Sheerness. It would be the largest, non-nuclear explosion we have seen in our lifetime,' says Captain Bain.
'So that's why we're going to see it.'
No wonder there's a bar onboard.
This enduring fascination with the SS Montgomery is one of the reasons why Jetstream Tours have been bringing boats here for a decade. Meanwhile, a paddle boarder was pictured some time ago leaning against the mast, there are stories of people fishing off it and having picnics on the deck, and Bain still sees sailing boats in the exclusion zone, passing between the buoys.
'Maybe it's the fear of missing out,' he says, once we've safely circumnavigated the site and decanted hungry travellers at Queenborough, a sleepy town on the north Kent coast. 'The last opportunity to see the masts in their natural state.'
So why aren't people sailing away from this wreck rather than towards it? Maybe the answer comes from someone who has been living with the possibility of explosions and tidal waves her entire life. Veronica Cordier is a former Chair of The Isle Of Grain Parish Council, just a few kilometres away on dry land. To her knowledge they have never been consulted about any plans to safeguard their community from the SS Montgomery, despite the fact they're also home to the largest liquefied natural gas terminal in Europe… and 28 petroleum storage tanks.
'You know what, we only think about it when it's in the media,' she says. 'We've got so used to it just being there.'
So she's not worried?'Well, I'm not happy it's there, and I'd be worried about what would happen if it did blow up of course. But then again, with the industry on the Isle Of Grain, it's just one of many hazards. If one goes up, they all go up!'
Which is one of the reasons why Professor Alexander talks of blast walls along the Kent coast needing to be installed if the SS Richard Montgomery was really going to be salvaged and made safe.
He's been studying, researching and teaching about the SS Montgomery at UCL since 2018.
'It's fascinating. After the war, there were lots of ships sunk with munitions on them, some deliberately. Just about everything was salvaged and cleared away, but not the Montgomery.'
But why not? Professor Alexander thinks the government attitude has been one of 'the longer it's left, the safer it gets'. But in the course of his research he went to Defence Munitions Kineton in Warwickshire – the largest ammunition depot in western Europe and home to the Defence Explosive Ordnance Disposal, Munitions and Search Training Regiment. Speaking to experts there, it became quite clear to him that most bombs do not get safer over long periods of time.
'I've made documentaries about the SS Montgomery, but I've never sailed around it myself,' he says. 'That was a deliberate choice. I find it gives me nightmares.'
Perhaps you'd expect a professor of Emergency Planning and Management in UCL's Department of Risk and Disaster Reduction to find the risk here. It's his life's work, after all. But does he find the current situation ever so slightly irresponsible?
'I suppose I do,' he says. 'Several things could happen. The wreck is disintegrating, and that will accelerate over time. That's quite clear from the reports – and as that happens it might disturb or affect the state of the bombs.
'Then there's the possibility of either a navigational error or a technical failure on a ship that then sails into the Montgomery. We've nearly had that – in 2010 a Danish tanker was heading straight for it with a cargo of one of the components of TNT!'
'You've also got to consider terrorism or deliberate interference – during the London Olympics the SS Montgomery was under heavy surveillance.'
Which is likely one of the reasons a 'Notam' – or notice to airmen, saying no-one is allowed to fly under 13,100ft across the exclusion zone was implemented in May this year. So not quite a no-fly zone but there's clearly serious enough concern to implement something approaching it.
Not quite enough to solve the problem once and for all, though. Four years ago, there was a tender won to remove the masts entirely but the subsequent lack of action on that front, says Professor Alexander, is because in the preparations for the footings necessary to complete the work, 67 'foreign objects' were found on the seabed.
'They were bombs,' he believes. 'Some have clearly fallen out of the Montgomery. Others were probably dumped there by fishermen when they came up in their nets – it's much easier to unload them in the exclusion zone.'
So there's been no progress, no plans since. Maybe that's because some of the salvage studies have talked about evacuating Sheerness for a year – it's why Professor Alexander talks of blast walls and robotics being more realistic.
'But it would be expensive.'And that's the real issue here, one senses. As Cordier puts it, 'these are financially straitened times aren't they? Governments aren't going to pay millions to make it safe.'
Easier, then, to put their trust in an adequate survey. Nevertheless, Professor Alexander does have some sympathy with this approach.
'It is unlikely it would all go up at once,' he admits. 'There's different types of bomb in there with different mechanisms. We don't really know to what extent they are fused, either.
'So you might have some bombs going off and some big explosions, but not all at once. It is a precarious situation, though.'
Just how precarious is a question for the Department for Transport to answer. We invite them to come out on the water with us and show us what work is being done to secure the SS Montgomery. They prefer to tell us there is no indication that the further degradation of the structure has increased the risk associated with the wreck – and that recent reports of shipping entering the restricted zone were inaccurate.
But they do anticipate continuing work on the project to reduce the height of the wreck's three masts 'within the next year'. That's the project, not the actual works themselves.
A Department for Transport spokesperson said: 'Our priority will always be to ensure the safety of the public and to reduce any risk posed by the SS Richard Montgomery.
'The condition of the wreck remains stable, and experts are continuing to monitor the site. As part of their ongoing monitoring, they have updated advice on how authorities can further minimise risk and recommended that pilots and operators do not fly in a limited area around and above the site as specified by the Civil Aviation Authority.'
All of which would seem to suggest Captain Bain will be sailing passengers around the SS Richard Montgomery for some time yet.
'I haven't seen decay,' he says. 'It managed to last all winter and the chances are, if anything is going to happen, it will happen in a gale force wind, in bad weather.'
But, after passing them hundreds of times since Jetstream Tours started a decade ago, he has noticed that the masts are moving, 'they are rocking backwards and forwards'.
And on occasion he has been asked to intervene when other vessels have gone too close.
He adds: 'I've seen sailing boats in there, passing between the buoys. People just don't really know. And we sometimes do get tasked by the Port Authority to see if we can get names of a particular vessel.
'We don't like grassing people up, but at the same time it's there for security. Nine out of 10 times they just don't know.'
So for now, the SS Montgomery remains something of a mawkish tourist attraction. And unless it does actually blow to smithereens, Professor Alexander can't see that changing any time soon.
'I got all the files about the SS Montgomery from the National Archives,' he says. 'And do you know what that told me more than anything? A typical British government meeting presided over by the Prime Minister will be 20 minutes of telling people about a subject they don't know anything about, 20 minutes of prevaricating, and 20 minutes to decide not to do anything.'And on that bombshell… the next trip to the SS Montgomery leaves on Tuesday.
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