Standing 11km off the Suffolk coast in Britain, it is the self-proclaimed smallest micro-nation in the world.
And for more than half a century, Sealand - a wind-lashed Second World War naval fort whose main platform, some 18m above the North Sea, can only be reached by being winched up by crane - has seen off not only German advances but those from the British government, too.
Now, with rising uncertainty over Brexit, the sovereign state is receiving hundreds of applications for citizenship each week, the Daily Telegraph reports .
According to Michael Bates, the principality's 67-year-old prince, would-be Sealanders are inspired by the ruling family's "desire for freedom from authority" - as well as its black passport, embossed with two crowned sea creatures.
Prince Michael describes himself as a "dual citizen", having been 14 when he first clambered aboard the decommissioned HM Fort Roughs, built as a Second World War defence.
It was his father, Roy, who declared it theirs in 1966 after eyeing it up as a potential site to run his pirate radio station.
Designed to defend shipping routes from German attack, it was by then abandoned and, when the Marine Broadcasting Offences Act was introduced in 1967, Bates Snr declared independence on the grounds that it was in international waters and beyond the jurisdiction of the British courts.
Unable to wrest it off Bates, the government sent the military to destroy other long-derelict wartime forts around the coast, lest other people get ideas.
Sealand has remained outside of British control, the first family says, ever since.
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Which is quite some feat, as Prince Michael, a barrel-chested Del Boy-type with a gap between his front teeth, knows well.
He took over the running of the place - which the government once described as having the potential to become the "Cuba off the east coast of England" - when his father died in 2012.
While it is yet to become a guerrilla state, it has seen more than its share of action.
Indeed, on reading tales of the place's survival efforts over the years - a 1968 "swashbuckling incident" that landed the Bateses in court; a coup attempt a decade later by German businessmen via helicopter, which ended with a 26-year-old Prince Michael bound by his elbows and knees in one of the fort's 21 rooms for days, a fire in 2006 - you wonder how it has continued to rise from the ashes.
That feeling does not dissipate in Prince Michael's company: our rain-smattered boat ride to the 550 sq m slab, which can be visited by invitation only, involves tales of whale-spotting with Jean-Michel Cousteau in Mexico and encounters with Simon Cowell's PA during a first-class flight.
Nor when we sit down for a cup of tea in Sealand's kitchen - a neatly done Ikea job, all cream cabinets and silver handles.
He doesn't live there now - that's the job of Michael Barrington, its caretaker, or "Head of Homeland Security" (the most inhabitants Sealand has had at any one time is in the low dozens) - but has spent much time here over the decades, sleeping out in the open during his mid-20s when bids at recapture were at their most furious.
The wind whipping around the place on the rainy September day we meet does not make an al-fresco arrangement look an enviable task.
But Sealand inspires a kind of devotion at once impressive and destructive.
"It didn't help much," Prince Michael reflects of his first marriage to the mother of his three children, partly down to the financial strains of pouring family finances into the place - a pressure that has since eased due to the success of their Essex cockle business and doling out Sealand "titles", which cost up to £499.99 ($968.80).
Barrington, a former engineer on Radio Caroline whose glasses are fixed with a little square of green and yellow tape, agrees that his loyalty hasn't weathered well with "lady friends", who see his service as "wasting your life".
He was close with Roy and his wife, Joan; in fact, the inaugural prince was like a "second father" to the island's sole resident, who returns to land every couple of weeks to swap with his "oppo", who takes charge while he's away.
"We were two mavericks together, as bad as each other," Barrington reflects of Roy, who died seven years ago tomorrow.
"He put Sealand before anybody, before his family."
It must have been hard, I ask Prince Michael, to be heir apparent to a man like Roy Bates, who fought in the Spanish Civil War, aged 15, and later became the youngest major in the British Army, serving in the Middle East and North Africa.
"My dad saw the war as a huge adventure," his son recalls, adding that he "enjoyed it" - in spite of being a prisoner of war twice.
Prince Michael's tack with his own sons, aged 32 and 30 and raised on terra firma in Essex, has been different; they work together maintaining both Sealand and the cockle factory.
His youngest, Charlotte, a 26-year-old canine beautician, stays separate from the goings-on of the world's smallest independent state, which stopped issuing passports a few years ago after forged documents landed the principality in hot water. (Before the 9/11 attacks, they could be used for international travel with ease, he says.)
She has been more vocal on the matter of her father finding a partner.
"My daughter always thought I should go for a woman more my own age," he says of Mei, 47, whom he met on Tinder three years ago and has joined us on our jaunt.
A former major in the Chinese army who he calls his "exotic little catch", they married in Thailand last year and now live with her 17-year-old son, also named Michael, in Leigh-on-Sea.
In spite of being a "Princess", she still works, driving her Maserati to her job in VIP customer relations at the Empire Casino in Leicester Square.
Almost inevitably, Hollywood has come calling - repeatedly.
"We have a producer, a household name director, and a scriptwriter, but Hollywood's a very flaky place, and until it's done, it's not done," Bates says.
"Everyone says it's a love story," he reflects. "Mum and Dad really did love each other. But the Sealand story is more of an adventure."
Prince Michael documented its escapades in his self-published 2015 memoir, Holding the Fort.
His stories are wild, often unbelievably so - when I challenge him on his claim that he was once locked up with Hitler's favoured filmmaker Leni Riefenstahl's son (she had no children), I am left wanting - but he is surprised that anyone could doubt the veracity of a life that he says really has been stranger than fiction.
And he is confident about its future.
"We won't lose this place," he says. "I know it's a paradox, but old Blighty's a wonderful place to be involved with. We just have different values."
How those values might change as the UK's international position shifts is still in flux.
If Sealand's history is any indication, though, it will take more than the breakdown of a union to uproot the sturdy little nation in the middle of the sea.