In 1944, the SS Richard Montgomery, a Florida-built cargo ship laden with 1,500 tons of explosives, ran aground and broke in half in the Thames Estuary in England. The ship was never salvaged and remains in place to this day—where it may be a ticking time bomb that could set off a damaging rogue wave.
The Richard Montgomery was a Liberty Ship, a type of transport ship meant to be manufactured quickly and in large quantities during World War II. Liberty Ships could carry troops or dry cargo, and could be constructed in as few as 42 days—in sum, 2,710 were built to support the war effort.
In August 1944 the Richard Montgomery set sail for France loaded with supplies and munitions. Awaiting a convoy to join, she ran aground on a sandbank near Shearness. The next day, while stevedores were offloading her cargo she snapped in half and sank with all that explosive material still on board.
Whatever happened next? Nothing. According to Yahoo News UK, the ship is still in place, marked as a maritime hazard and monitored by the UK's Maritime and Coastguard Agency. An exclusion zone 1,640 feet wide protects the wreck. Here's drone footage of the wreck as it is today.
The 1.5 kiloton of explosives is a serious concern. By comparison, a typical air-to-ground bomb used by modern U.S. and U.K. forces weighs just one ton. The Hiroshima atomic bomb had an explosive yield of 16-18 kilotons. The likelihood of the ship exploding is generally regarded as low and the wreck is considered "stable", but a recent government report stated that an explosion could still happen if another ship collided with the wreck or the cargo shifted in place.
Munitions ships have blown up before, and with devastating consequences. In 1917 the SS Mont-Blanc loaded with war material exploded in Halifax Harbor, Nova Scotia, with the force of 2.9 kilotons, killing nearly 2,000 people. In 1947, the Grandcamp—another World War II-era Liberty Ship—exploded in Texas City harbor, killing 581 people.
While the Richard Montgomery is far enough away that an explosion wouldn't cause any direct harm to the local population, it would likely generate a four-foot rogue wave powerful enough to flood nearby communities. It has also become a potential dealbreaker towards the expansion of Heathrow International Airport, where a floating runway under consideration would sit just 1.5 miles from the wreck.