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Seen from a boat approaching from San Francisco, the former prison dominates tiny Alcatraz Island.

ALCATRAZ ISLAND, California -- To escape from this prison built on jagged rocks in the San Francisco Bay, an inmate needed to swim through poisonous jellyfish, numbness, exhaustion, tides, and angry guards trying to kill him.

"It's the shock of the freezing water, the sudden extreme exercise, not getting enough oxygen," said Kent Myers, an obsessed swimmer who spends much of his free time in and along the Bay, recreating a prison escape from Alcatraz Island to San Francisco's shore.

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In 1946, a "Battle for Alcatraz" erupted when a group of prisoners attacked guards and seized some weapons, resulting in a shoot-out which killed three inmates and two officers.

"A huge panic overtakes you, and you think: 'Shit! There's no way I'm gonna make this! What the hell was I thinking?'"

Alcatraz juts from the choppy waters more than a mile from the city's steep streets, and three miles east of the reddish metallic lace of the Golden Gate Bridge.

Originally a U.S. fort in 1859, Alcatraz became a military prison in 1907, and an infamous maximum-security Federal Penitentiary from 1934 to 1963.

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Maximum security.

Alcatraz caged some of America's worst inmates, described as men too dangerous to be held in other prisons, including Al "Scarface" Capone, and George "Machine Gun" Kelly.

In 1969, native American Indians seized the unoccupied island, but were expelled in 1971.

Today, the grim facilities are operated by the government's National Park Service, and is San Francisco's most popular tourist attraction.

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Two maintenance workers rest while repairing Alcatraz, which suffers from age and weather.

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A tourist poses near the prisoners' cell block, with a backdrop of San Francisco more than one mile away, including the Dolphin Club which appears on the right, sheltered by a breakwater.

Myers keeps an eye on the island's ominous prison architecture from the Dolphin Club, which nestles on San Francisco's prestigious northern shore, west of Fisherman's Wharf.

Describing his successful August swim from Alcatraz to the Dolphin Club, Myers said in an interview: "The waves were awful rough at the beginning, like two- to three-foot swells. You're getting sloshed around so much, you start getting seasick, and sometimes you reach out and there's no water if you're on top of the wave.

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An inmate's cell, with his personal items kept as an exhibit, also displays a hole he dug through the wall, under the sink, in an effort to escape.

"Other times, you attempt to take a breath, but suddenly you're three feet below water. I found myself being able to breathe only about once out of every two to three tries," Myers said.

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Kent Myers.

"Basketball-sized jellyfish" are also a problem. "If you get stung near the ribs, that can lock-up your arm.

"The fog adds to the ambiance. When starting out, we could just barely make out the city silhouette, and that's pretty spooky.

"It's like you're swimming off into nothingness."

His fastest swim from Alcatraz to the club lasted 75 minutes, though it can take some people twice as long.

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Kent Myers, an obsessed swimmer, spends much of his free time in the Bay, repeatedly recreating a prison escape from Alcatraz.

"I swam it three times, successfully, all this year," said Myers, who was born on May 20, 1962 in Detroit, Michigan, and moved to San Francisco in 1987.

"The record is 22 minutes, set by the Dolphin Club's Suzanne Heim, on the New Year's Day swim this year."

Dolphin Club members insist on some prison-era realism -- no wetsuits allowed -- though they wear goggles, earplugs and an insulated swim cap.

Desperate prisoners who dove into the water from Alcatraz did not have other perks Dolphin Club members enjoy, including the comfort of nearby rescue and guide boats, plus daytime's light instead of an escapee's preferred darkness.

Myers can also choose water temperature, tides, currents, and other conditions.

"In September the water temperature is around 63 degrees Fahrenheit (17 Celsius), in January it's around 47 (8 Celsius)," he said.

Unlike Myers, the handful of prisoners who jumped into the water did so in a frightened, sudden rush, unable to time the powerful currents, which can vary from one to six knots.

"And there weren't squads of people trying to kill me while I was doing the swim. There's really no comparison, the prisoners' swim was much harder."

Alcatraz boasted no one could survive an escape, which deterred many inmates from ever trying, but 36 prisoners tried to flee.

"All but five were recaptured, or otherwise accounted for," according to an official statement from Alcatraz.

Unaccounted men presumably drowned.

"One guy officially made it to San Francisco. John Paul Scott, on December 16, 1962. That's a cold time. He made it to San Francisco and beached himself near Fort Point -- the foot of Golden Gate Bridge. That's about a 3.5-mile swim," Myers said.

"He collapsed on the beach and was taken to a hospital where the cops busted him shortly thereafter. The poor guy used every last ounce of energy to stay alive. At that point, that was all that mattered, getting to dry land, not crawling 20 more feet to hide in the bushes."

Some inmates who tried to swim from Alcatraz quickly turned back, and climbed onto the island, unwilling to take the risk.

"The famous guys, the Anglin brothers, disappeared without a trace. I believe they drowned during the swim," Myers said, though others suggest the brothers may have survived.

Thousands of people now try to do the swim each year -- mostly wearing wetsuits -- during commercialized events.

At least two sports enthusiasts died in recent years, including Sally Lowes of Houston, Texas, who perished in August 2007 during the popular "Alcatraz Challenge."

Myers, meanwhile, dreams of other prison island swims he wants to do in the future.

"Devil's Island, from the Steve McQueen movie 'Papillion', is on my list. It's seven miles to the mainland, but the water's warmer. I think I'd have a shot at it."

America's infamous Guantanamo Bay prison on the island of Cuba is not so attractive.

"I think we all played cops and robbers as kids, and at some level we fantasized about the big ones like Al Capone or 'Machine Gun' Kelly, and you might imagine yourself tough enough to hang with that crew and make the escape.

"Same with Devil's island. I could see myself joining the French Foreign Legion after some heavy ruined romance, then getting thrown in the brig for beating up my officer, and next thing I find myself living in a jail cell on Devil's Island planning my escape.

"But I don't romanticize about Guantanamo Bay.

"I suppose I'd try to swim up the coast north towards the rest of Cuba, away from the American base. That's probably the most realistic [route], but I have no idea of the currents.

"It's 100 miles to the next island-country, like Jamaica or Haiti. I wouldn't stand a chance."

Richard S Ehrlich is a Bangkok-based journalist who has reported news from Asia since 1978. He is co-author of "Hello My Big Big Honey!", a non-fiction book of investigative journalism, and his web page is http://www.geocities.com/asia_correspondent