Visible from Suffolk's beaches, the 'micronation' of Sealand has had a stormy history ever since the fortress was built during the Second World War.
Since the Maunsell fort was put in place, it has served as a base of operations for a pirate radio station in the 1960s, a family home for a self-proclaimed royal family in the 1970s, and as a base of operations for websites in the early 2000s.
Consisting of a floating base, a deck and two hollow concrete legs for the crew to live in, the fort — originally called HM Roughs Tower — was dragged into place over a sandbar and sunk in 1943.
During the war, it was used to defend nearby estuaries from German aircraft.
But in the 1950s the forts were abandoned. And by the 1960s, they made tempting bases for people looking to set up pirate radio stations.
One of those pirate radio broadcasters was Paddy Roy Bates.
Known as Roy Bates, he took over HM Roughs Tower in 1967 and went on to declare its independence and style himself Prince.
Michael Bates, the current ruler of Sealand, inherited the title of Prince from his father.
Speaking about Sealand's early piratical days, Prince Michael said: "When I was a boy there was no pop music on the radio. Transistor radios you could carry around were a fairly new thing and very expensive, but they were just coming into the mainstream.
"If you wanted to listen to pop music, you would have to tune into Radio Luxembourg, which would come in and out at night as it bounced off the ionosphere."
This gap in the market motivated a number of entrepreneurs, including Michael's father, to set up privately run pirate radio stations on ships and platforms just off the coast.
Prince Michael said: "There is a bit of a misconception on the internet — we never actually put a pirate radio station on Sealand. We had one on another Maunsell Fort — the Knock John Fort off Essex — broadcasting Radio Essex.
"When the government brought in the Marine Offences Act (in 1967), it drew a line across the Thames Estuary and said everything inside it was British territory.
"Dad got closed down and started looking for somewhere else."
The search led the family up the coast, to HM Rough Towers — the fortress which would become Sealand.
Prince Michael said: "We went out on Christmas Eve 1966 and took over the Fort Roughs. It wasn't a radio station, but there were some caretakers on it from Radio Caroline.
"We just climbed up — it was a really calm night and they came out of the building."
Prince Michael claimed one person was armed with a rifle but there was "no violence".
"We just said we were taking them off," he said. "My father and I then took them into Harwich."
However, Radio Caroline attempted to take the platform back.
Prince Michael said: "There were seven or eight different attempts which are detailed in my book.
"What were they using it for? Nothing!
"The Marine Offences Act had just come in and Radio Caroline was using it as a resupply base for helicopters.
"I think the idea was they wanted somewhere to keep supplies, fuel, and stores to keep the radio station running.
"I was 14 when all this trouble was going on out there — it was my dream really at the time.
"I was always brought up with a bit of Boy's Own Annual stuff. It was interesting to me to defend the place.
"I didn't really consider that I could get hurt at the time — I was like my father — I thought I was indestructible.
"A lot of my friends who've read my book said I should be dead."
Since its pirate radio days, Sealand has gone on to have various uses.
The tower was used as a base of operations for web-hosting companies in the early 2000s.
In 2007, it was reportedly in sales talks with controversial Swedish website The Pirate Bay, which was looking for a new base.
Prince Michael added: "Whatever we've done we've always tried to be aware of our responsibility to the outside world — the international community.
"That's why we stopped issuing passports— we don't want to give people a pathway to terrorism."
Sealand currently supports its continued independence through the sale of noble titles.
Via its website, people can pay to become a Knight, Lord, Count, or Duke of the principality.
For more information on Sealand visit its website.
Prince Michael of Sealand has also written a book on the principality's history.
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