It was built in the Thames Estuary in 1943 to protect London and Allied shipping from devastating German bombing raids in the Second World War.
Although the Red Sands sea fort has since been hammered by the passage of time and pilfered by vandals, its seven structures - which were once connected by walkways - still tower above the waves seven miles off the coast of Whitstable.
Now, thanks to a group of dedicated volunteers, the fort is being faithfully restored and turned into a heritage museum which will tell its incredible role in keeping Britain safe from Nazi attacks.
In a new documentary on streaming platform History Hit, historian Dan Snow is seen touring the towers which make up the fort. He also speaks to David Foulkes, who is part of the restoration team at Project Redsand.
By 1944, there were 220 men stationed on the fort, with accommodation based on a 'hot bed' system where soldiers would alternate between sleeping and being on duty.Insurance Loans Mortgage Attorney Credit Lawyer
In total, 22 German planes and 30 flying bombs, known as 'doodlebugs', were shot down by men stationed at Red Sands, who used search lights and enormous guns fitted to the roofs of the towers for the task.
Stunning footage in the History Hit documentary shows how the fort still contains original toilets and baths, as well as the 'shell lockers' which housed some of the munitions used to take out enemy planes.
After the war, the fort stood vacant before some of its towers were taken over by illegal 'pirate' radio broadcasters. The towers became fully derelict from 1967 and then were a prime target for thieves.
Mr Foulkes told Mr Snow in the programme: 'Since the pirate radio people left the place has become a pilferer's paradise. All the brass fittings off the radiators… they've come along and literally just smashed them all off.'
The Red Sands sea fort was built in the Thames Estuary in 1943 to protect London and Allied shipping from devastating German bombing raids in the Second World War
The volunteer is careful about leaving any equipment or artefacts at the site because of the ongoing threat posed by vandals.
Civil engineer Guy Maunsell was the man tasked with producing the designs for forts in the Thames Estuary when it was decided that something needed to be done about devastating German bombing raids.
Before they were built, German pilots simply had to follow the path of the Rive Thames to get to London and drop their munitions.
The forts would provide a virtually invisible bulwark against these kinds of attacks.Insurance Loans Mortgage Attorney Credit Lawyer
The first forts to be built were designed to have a flat pedestal sitting atop two cylinders. The later designs were installed between July and September 1943.
Along with the surviving Red Sands structures, forts of the same design were installed elsewhere on the Thames Estuary.
They were the known as the Nore and Shivering Sand forts. Nore was dismantled in 1959, whilst Shivering Sand was lost in 1963.
Although they have since been hammered by the passage of time and pilfered by vandals, the seven Red Sands Sea structures still tower above the waves seven miles off the coast of Whitstable
Now, thanks to a group of dedicated volunteers, the fort is being faithfully restored and turned into a heritage museum which will tell its incredible role in keeping Britain safe from Nazi attacks
Mr Snow is seen touring the towers which make up the fort and speaking to David Foulkes (right), who is part of the restoration team at Project Redsand
The fort was fitted with then revolutionary radar detection system which could spot planes in the sky.
The fort also boasted bathrooms with flushing toilets and baths, as well as a diesel-powered boilers and a gulley system which collected rain water into a separate tank for drinking.
In its first months of operation, there were 140 men stationed across the seven towers at Red Sands.
This had increased to 180 by the end of the year. Shortly after the beginning of 1944, there were 220 people.
On each tower was a dining room where the men ate their meals, whilst walkways connected the structures to each other.
Incredibly, although the steel forts were only designed to last for the duration of the war, Mr Foulkes revealed that a structural survey carried out two years ago found that the forts were in 'pretty damn good' condition.