77-year-old wreck, SS Richard Montgomery, is monitored and there is an exclusion zone around it but it is not far from the main shipping lanes into the capital.

The Department for Transport (DfT) wants to trim the masts as it is feared they could fall on to the ship below and cause a detonation.

It follows remedial work to trim the rigging and such from the masts (above the water line) in October 1999, which was carried out with the aim of reducing stress levels.

Businesses have been told the masts will go in June.

The masts of the wreck of SS Richard Montgomery, which are due to be trimmed. Credit: Jason Richardson / Alamy Stock Photo

A DfT spokesperson said: “We continue to monitor the wreck of the SS Richard Montgomery closely and it is understood that it is in a relatively stable condition.

“Expert wreck assessors are now undertaking detailed surveys which will inform future work to reduce the height of the masts.”

Professor David Alexander, from University College London, is an expert in risk and disaster reduction and has studied the SS Richard Montgomery in detail.

He told PBO: “The DfT spokesperson was right – the wreck is in a “relatively” stable condition. Emphasis on “relatively”.

“Five years ago the surveyors gave it between eight and 20 years before it starts to disintegrate seriously.

“Liberty ships were made with low-grade steel and slapdash welding; expendable ships that were easily sunk in the Atlantic by U-boats.

“Mild steel deteriorates over time in cold water.”

Professor David Alexander, from University College London

Why not just remove the explosives?

Professor Alexander thinks it is time the authorities removed the explosives, although he admitted the work would not be cheap, not least because “there’s only one company in the world that could do that” – Smit (of the Netherlands) – and would “probably need robots”.

He said in the worst case scenario or ‘top event’: “There could be a very small tsunami as a result of a pressure wave but there is not enough depth of water to generate a large one (or so I believe…).

“Other events might include smaller but sporadic explosions and an ungovernable situation. If a liquefied natural gas carrier were to plough into the Montgomery then all hell would break loose.

“Nevertheless, a top event is not inevitable. That said, the blast effect on the nearby Isle of Grain could be spectacular.”

SS Richard Montgomery wreck in the Thames estuary. Credit: Rob Powell / Alamy Stock Photo

Masts pose a hazard

Regarding the masts, Professor Alexander added: “If the support structures disintegrate, the heavy masts could sink through the decking and compress the bombs in the holds.

It is not known how many of the bombs are fused.

Regarding the salvage and clear-up, Professor Alexander said: “Salvage has been resisted so far because it is argued that the population of the Isle of Sheppey would have to be evacuated for up to a year. (With one set of bridges, by the way, emergency response on Sheppey would not be easy.)

“I think it could be done by building temporary blast walls on Sheppey and Grain, and restricting the movement of people on the island.

“The salvage would be made complex by the different types of bombs and their condition after 77 years.

“Meanwhile, the wreck is disintegrating.”

SB Lady of the Lea passes of the masts of the sunken SS Richard Montgomery. Credit: Rob Powell/Alamy Live News

SS Richard Montgomery’s history

The SS Richard Montgomery was a US Liberty Ship of 7146 gross tons.

She was built in 1943 by the St John’s River Shipbuilding Company of Jacksonville, Florida and was one of more than 2,700 of these mass-produced vessels built to carry vital supplies for the war effort.

In August 1944 the ship was loaded with a cargo of some 7000 tons of munitions and joined convoy HX-301 bound for the UK and then on to Cherbourg.

On arrival in the Thames Estuary, the vessel was directed to anchor in the Great Nore anchorage off Sheerness.

The ship was to await the formation of a convoy to continue the journey across the Channel.

However, on the 20 August 1944, she dragged her anchor in the shallow water and grounded on a sandbank, running east from the Isle of Grain approximately 250 metres north of the Medway Approach Channel.

The vessel grounded amidships on the crest of the sandbank. Intensive efforts began to unload her cargo.

Unfortunately, by the next day, a crack appeared in the hull and the forward end began to flood.

The salvage effort continued until the 25 September, by which time approximately half of the cargo had been successfully removed.

The salvage effort had to be abandoned when the vessel finally flooded completely.

The wreck of the SS Richard Montgomery remains on the sandbank where she sank.

The wreck lies across the tide close to the Medway Approach Channel and her masts are clearly visible above the water at all states of the tide.

There are still approximately 1,400 tons of explosives contained within the forward holds.

A yacht passes the wreck of SS Richard Montgomery. Credit: James Bell/Alamy Live News

Wreck co-ordinates

The wreck is designated under section 2 of the Protection of Wrecks Act 1973, which means that there is a no-entry exclusion zone around it.

The wreck is clearly marked on the relevant Admiralty Charts.

The exclusion zone is defined by the following co-ordinates:

51° 28’ 04” N 00° 47’ 12” E

51° 27’ 57” N 00° 47’ 22” E

51° 27’ 50” N 00° 47’ 11” E

51° 27’ 58” N 00° 47’ 01” E

Medway Ports is contracted by the Maritime and Coastguard Agency (MCA) to mark and guard the wreck.

This includes the provision and maintenance of warning notices on the wreck, which are fastened to the masts.

Medway Ports is also contracted to provide and maintain a circle of buoys around the wreck to ensure that shipping avoids the area.

The wreck is also under 24-hour radar surveillance by Medway Ports. Medway Ports, whose operations room is within sight of the wreck, provide a first line of response to any incursions within the area.