The Bush administration built a series of prison camps for the 779 detainees who have passed through the place, including a still-secret building for former CIA captives. The Navy also put in a sports field, renovated housing and leases trailer parks for rotating detention center forces. And it has a variety of overlapping and at-times unreliable communications systems — from a contract cable TV and Internet plan that troops must pay for, to a no-charge, molasses-slow Wi-Fi system and sophisticated teleconferencing for the commanders.

Rear Adm. David B. Woods, ending 10 months as prison camps commander, revealed last week that he had staff cut the prison’s monthly telephone bill from $21,000 a month to $5,000 — no small feat, he said, because the Pentagon lets captives make phone calls to family across the globe as part of a Red Cross program.

Cuba doesn’t get a veto on the project, or any activity on the base, which is surrounded by 17.4 miles of fence line patrolled by Marines in southeast Cuba. The United States says it’s a lawful tenant under a 1934 treaty and sends an annual rent check from a Swiss bank for $4,085 to Havana — even after Fidel Castro told the U.S. military to get out in the 1960s.

The base captain meets monthly with his Cuban counterparts. During a recent meeting, Hibbert said, he alerted them that the surveyor ship would be off base waters this summer. He said he got no opposition from the Cuban military after he characterized it this way: The U.S. is setting up “reliable, more robust communications” to update the “antiquated system we have now.”

Even before that, Hibbert said, U.S. officials sent a diplomatic note to Havana, notifying Cuba about the fiber-optic program.

A State Department spokesman would not disclose what the Cuban government was told about the project, or when. It’s policy to keep such communications secret, said William Ostick of the Western Hemisphere Affairs division.

Nor would the Pentagon disclose where the cable would likely come ashore in South Florida after passing through the Windward Passage east of Cuba and emerging from the Atlantic Ocean — Key West, just 80 miles north of Havana, Miami, or somewhere else. Key West and Miami are roughly an equidistant 600 nautical miles from Guantánamo on a path around the eastern end of the island.

The technology is not new.

Telegraph then telephone cables have been on the ocean floor for more than a century, experts say, and for a time the base had a phone line from Guantánamo’s aptly named Cable Beach to Jamaica. Undersea fiber optics came into their own about 30 years ago, according to Vincent Chan, a professor of electric engineering who specializes in the subject at the Massachusetts Institute of Technology, “and they get better every year.”

“It’s routine,” he said. “Every time you make a long distance to call to Europe or Asia you’re basically using this technology. They’re not using satellites any more.”

At this stage, he added, it’s easy to install and a 600-nautical-mile link could be accomplished in six months, depending on the contractor and how much infrastructure needs to be built at either end.

Ships with massive coils of coated fiber-optic cable the circumference of your wrist reel the cable into the sea. Think of a commercial fisherman, Chan said, but “instead of deploying a trap they’re deploying a cable.”

Fiber-optic cables require an undersea signal amplifier — a laser — at 30-mile intervals to keep the signal strong.

The only place where the cable might be susceptible to sabotage, he said, is in shallow water, where it emerges to link to a land station. Most of it is so deep in the ocean the only danger is a break, in which case a repair boat would reel it back out and reconnect it.