On the 5th of July 1944 the 7146 ton Liberty Ship number 243756 left Hog Island in the US and began the long journey to the UK. Her first port of call was part of convoy HX-301. These convoys enjoyed a low loss rate, losing only 0.6% of all ships which used this crossing route. The reason for this was first the convoy went via Halifax, where they picked up more ships then took a long 3165 North East route to Liverpool. Even with an average speed of just 8.5 knots the 130 ships, including twelve US Landing Ships Tank, HX-301 reached Liverpool without enemy incident.
It is reported one of the escorts was an aircraft carrier, and that one of the transport ships had several young ladies on board. Upon finding out this fact the crew of the aircraft carrier put up a plane that dropped a gift of vegetables in a bouquet to the ladies on the transport. However the eyewitness says that this drop missed the ship and was last seen floating past.

Upon reaching Liverpool the convoy split and the ships went their own separate ways. Liberty Ship 243756 sailed for London, along with seven other Liberty Ships. Once reaching London they would hold until another convoy could be formed to cross the channel for the newly opened port at Cherbourg where her cargo of bombs, including several hundred blockbusters, would be unloaded to arm the RAF planes flying against Germany. Upon arrival at London she was assigned a mooring at the Great Nore Anchorage, covered by the Nore Forts.
These Maunsell Forts stick out of the sea on four giant legs, looking weirdly reminiscent of something from HG Well's War of the Worlds. Designed to protect the Thames Estuary from air and fast boats they were armed with a variety of AA guns, search lights and fire control centres. Each fort is linked by a walkway above the muddy sea. The concrete legs mounted on a base were floated out to be in position then sunk onto the sand banks. These sand banks were to cause the crisis.

Most Liberty Ships had a draft of about 28 ft. However ship 243756, named the SS Richard Montgomery, had a draught of 31 ft. The anchorage that was issued to the Richard Montgomery was a mere 33 ft deep. An argument broke out ashore at the control room for the area with the Harbour Master refusing the Assistant Harbour Master’s recommendation that the Richard Montgomery have her birth switched to a deeper one, currently occupied by a frigate. The frigate only had a draught of 24 ft. This argument became so heated that a superior naval officer intervened and sided with the Harbour Master.

On August 20th 1944 the wind changed direction, causing the Richard Montgomery to swing about, she then began to drag her anchor until inevitably she beached. Even worse she beached at the height of the spring tide which meant that even with removing all her ordnance she'd have to stay in position for several weeks before she could be re-floated.
Salvage efforts started on the 23rd of August, another ship came alongside and ran a steam hose aboard the Richard Montgomery to power the ship’s cranes. Then on the 24th the settling tides caused the Richard Montgomery’s back to break flooding several holds and letting some of the colossal amount of explosive contained within her holds to wash out onto the seabed. Salvage continued until late September when the operation was abandoned. So roughly 1400 tons of explosives lie in the mouth of the Thames Estuary, and have lain there since the end of the war. There is a debate over the question of the explosives still being viable or not. But what if they are?
SS Richard Montgomery as she is today. you can see where the currents have eroded the sand keeping her stable and upright.
Well we can look back to World War One to find a possible answer of what might happen. Coincidentally it happened at Halifax, the location Richard Montgomery’s convoy was named after. On 6th December 1917 the SS Mont-Blanc and the SS Imo collided in the Bedford Basin at about 0845. The collision toppled some barrels in the SS Mont-Blanc’s hull which split open spilling benzol, a highly inflammable liquid that caught fire from sparks caused during the impact.
The blaze spread throughout the ship and the crew were forced to abandon her. Some local boats tried to fight the fire after the SS Mont-Blanc beached itself. However at 0904 the fire reached the Mont-Blanc’s other cargo, explosives and guncotton for the French Army.
The Mont-Blanc exploded with the force of about 2.9 Kilotons! The blast vaporized so much water that the bottom of the harbour was briefly visible, and created a 18 meter Tsunami. The 90mm deck gun, melted out of shape was found 3.5 miles away and the shockwave was felt as far away as 129 miles. About 2000 people were killed, and 9000 injured.
The Halifax explosion, the cloud is nearly 12000 feet in height, so that gives you an idea of how far away this picture was taken.
One eyewitness and survivor described the scene. "The sight was awful, with people hanging out of windows dead. Some with their heads missing, and some thrown onto the overhead telegraph wires."
The Halifax explosion was in the middle of a single city in a sparsely populated country. The SS Richard Montgomery lies in the middle of one of the most densely populated regions.

Ground zero is to the extreme right of the picture. There's a sugar refinery in this picture...

Image credits:
dailymail.co.uk, bbci.co.uk, www.submerged.co.uk and exhibits.hsl.virginia.edu