All hands stand at attention during Naval Station Guantanamo’s 2011 Veterans Day ceremony on the parade field at Marine Hill.

MIAMI — The Pentagon has decided to lay an estimated $40 million underwater fiber-optic cable from Guantanamo Bay to South Florida, The Miami Herald has learned, in the latest sign that the military is preparing for detentions and other operations at the Navy base for the long term.

“It only makes sense to do if we’re going to be here for any period of time,” said Navy Capt. Kirk Hibbert, disclosing the project in an interview last week before ending a two-year tour as the Navy base commander.

Construction won’t start for more than a year. And communications won’t come online for probably two more years.

But the American military has already notified the Cuban military to expect a surveyor ship, the USNS Zeus, off the base’s coastline this summer — a first step toward getting the program funded and then out to bid.

The fiber-optics plan is the largest known infrastructure improvement for the base by the Pentagon, which has undertaken expansion and building projects in a mostly piecemeal and sometimes secretive fashion in the decade of housing war on terror captives there.

Army Lt. Col. Todd Breasseale said the Defense Information Systems Agency had done a “feasibility study” and put the tentative price tag at $40 million. It will require congressional approval, he said, and is in the fiscal 2013 budget.

At Guantanamo, Hibbert said increasing data delivery from the base, which has both the war court and the prison camps intelligence unit, had stretched satellite access from the outpost and planners studied whether to expand their “terrestrial system,” or go under the water with fiber optics.

Plus, satellite links are prone to interference during bad weather, when the century-old outpost may need connectivity the most. The base, population about 6,000, is like a small town with a seaport, airport and the detention center that houses 169 foreign men as captives, with 1,700 troops and contractors on temporary assignment to imprison them.

The Heritage Foundation’s Cully Stimson, who was in charge of detainee policy for the Department of Defense during the administration of President George W. Bush, said the investment makes short-term sense with the coming war crimes trials, notably of the five accused Sept. 11 plotters. But he warned that the investment in the infrastructure does not necessarily signal that the Pentagon is now preparing for detention of prisoners at Guantanamo forever.

“That naval station’s been around since 1903, and it will live long past the detention mission,” said Stimson, now Heritage’s chief of staff and senior legal fellow. “It may be a fiscally prudent use of taxpayer funds.”

The Pentagon also uses the 45-square-mile base as a contingency site for humanitarian relief operations. It has fields prepared to house in tents thousands of people who might flee social unrest or natural disaster in the Caribbean, as refugees from Cuba and Haiti did in the 1990s.

Even if President Barack Obama were to succeed in his ambition to close the detention center, Stimson said, the infrastructure there could be put to other use.

Maintaining Guantanamo is expensive, and the constant churn of prison staff adds to the cost. Navy Cmdr. Tamsen Reese, the recently departed public affairs officer, said the prison estimates it costs taxpayers $77 a day to house and feed a soldier or sailor assigned to detention center duty.

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 Guantanamo 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 Guantanamo’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 anymore.”

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.

