Two months after the D-Day invasion, the US Navy ship SS Richard Montgomery was transporting 6,000 metric tons of explosives from Philadelphia, USA, to France, to supply the Allied forces advancing into Europe.
The Montgomery dropped its anchor in the Thames Estuary to wait for a convoy formation that would then make its way to Cherbourg. The Harbourmaster instructed the captain of the Montgomery to moor at Sheerness middle sands.
On August 20 1944 the Montgomery dragged her anchor and ran aground on a nearby sandbank during a force 8 gale. When the tide receded, the unsupported ship broke its back against the sandbank and the crew were forced to abandon ship.
The cargo of the ship included 2,000 cases of cluster bombs, dozens of Blockbuster bombs and hundreds of more standard bombs weighing up to 1,000 pounds each.
A salvage operation began on August 23 to recover the 6,127 tons of munitions still on board. The ship’s hull broke open the next day, causing several holds to flood. The operation continued for a month, when the ship was completely abandoned on September 25 after it broke in two.
Since then, the ship, still containing around 1,400 tons of ordnance has remained on the bottom of the Thames for over 75 years. The shallow waters it lies in means the masts still protrude above the surface of the water, acting as a convenient indicator for the hazardous wreck’s location.
The Montgomery and its cargo are well known to authorities, who have placed signs on the masts and created a 500 meter exclusion zone around the ship.
It is currently the most surveyed and monitored wreck in British waters. These surveys have shown that the ships structure is heavily eroded, causing experts to worry that the masts could fall through the ship’s weak deck into the ordnance stored below.
Another concern is the deteriorated explosives and fuses will have become highly unstable, meaning they could detonate from a movement of the hull or shifting of the cargo inside.
The wreck has been left untouched due to the costs and danger involved with safely removing the explosives. A similar situation in 1967 saw an attempt at removing explosives from the wreck of the SS Kielce, a cargo ship that sunk in 1946 after a collision with another boat in the English channel, a few miles from land.
During the operation, the explosives detonated, causing an explosion powerful enough to damage buildings in Folkstone, about 4 miles away, and seismic shock registered 5,000 miles away.
The SS Kielce was deeper and further from land than the Montgomery, and contained much less explosives.
A 1970 study estimated that if the explosives were to detonate, it would launch a 3,000 meter column of water into the air, and send a five meter high tidal wave through the Thames, shattering every window in nearby Sheerness. Another more recent study estimated that the wave would be around 1 meter tall, significantly less, but enough to still flood some areas.
Authorities aim to remove the masts at some point, to climate the risk of setting off the explosives if they collapse, but even this is a complex and extremely dangerous task, due to the volatility of the cargo.
The ship is technically owned by the US government, but as it is designated a dangerous wreck according to according to Section 2 of the Protection of Wrecks Act 1973, the UK government is required to carry out regular inspections of the wreck site.
Recently, red buoys that mark the perimeter of the exclusion zone were removed for cleaning. Those buoys will be even more important once the masts are no longer there to serve as a landmark. The Ministry of Defence is providing experts to be present to guide the removal of the masts.