Masts Removed From Explosives-Laden Thames Wreck, but Bombs Stay Put

A delicate engineering job meant to head off a possible disaster near London has been finished, officials say. Crews have removed the three rusting masts from the SS Richard Montgomery, a U.S. shipwreck from World War II that still holds a vast quantity of explosives. The munitions themselves have not been touched, and experts say they will keep watching the site closely.

The Montgomery was one of about 2,700 ships built in the United States to support the Allied war effort. It ran aground on a sandbar off Sheerness in the Thames Estuary, roughly 40 miles from the British capital, in August 1944. The ship was carrying munitions meant to support the Allies after the D-Day landings. It broke apart during salvage efforts and sank, with an estimated 1,500 tons of explosives in its cargo holds.

For decades, the three masts poking out of the water were a familiar sight to local residents and passing vessels. Recent surveys, however, found the structure was deteriorating further, and there were fears the masts could collapse and set off an explosion.

Nolan Conway, a naval architect with Florida-based Resolve Marine Group, the firm hired to take the masts down, said the vessel had begun to lean. "The fear is the masts could have fallen onto the cargo itself, causing it to detonate," he told CBS News. He added that some of the munitions are believed to have pressure fuses, so an impact could potentially set them off.

The main challenge, according to Conway, was cutting the masts away without shaking the wreck or endangering workers. His team built a custom lifting frame to raise each mast clear without swinging or swaying. They also used a remotely operated underwater diamond-wire saw, which clamps around a mast with hydraulic arms and passes the saw through, so no divers had to enter the water.

U.K. maritime minister Keir Mather told the House of Commons this week that the "complex project" had been completed ahead of schedule and on budget. All three masts were removed at a cost of just under $13 million, according to The Guardian. Mather said the masts had put "significant load on the structure," and that taking them off reduces that risk and supports the long-term safe management of the site.

The explosives remain in place because removing them would carry considerable risks. Experts also disagree about what a detonation would do. Conway said estimates range from effects on the shoreline, to a tidal wave traveling up the Thames, to a fairly minor event that might only close a nearby shipping channel. "There's a large range of impacts, but none of them are really good," he said. Officials still judge the overall chance of an explosion to be low.

The government has long kept an exclusion zone around the wreck, which lies about 1.5 miles off the Sheerness coast. Mather said the site will continue to be subject to continuous monitoring and control through that zone.

The masts themselves are expected to be preserved. Mather said they have been moved to the Historic Dockyard Chatham museum, where they will be displayed in recognition of the ship's historic significance and its role in supporting Allied forces during the war. More than eight decades after it failed to reach Europe, the Montgomery and its cargo will stay where they came to rest, now entirely out of sight but far from forgotten.