Is the new Cold War between the U.S. and Cuba based on old Cold War spycraft?

The dark arts of intelligence and diplomacy are often compared to a chess match. But a former U.S. diplomat this week turned to a less sophisticated, but perhaps more apt, pastime as a metaphor for the weird, murky confrontation going on between the United States and Cuba.

“Remember that old board game Clue?” mused a former U.S. diplomat earlier this week. “You had to solve a murder by identifying the killer, the weapon and the venue: It was Colonel Mustard, with a knife, in the ballroom.

“Well, we’ve got a victim — U.S.-Cuban relations — and a venue, various houses and hotel rooms in Havana. But we haven’t got a suspect or a weapon yet. Not to make a pun, but we don’t have a clue.”

The expulsion of 15 Cuban diplomats from Washington announced on Tuesday, following a State Department decision to pull most personnel out of the American embassy in Havana, leaves diplomatic relations between the countries at half-staff.

It’s a startling turnaround from the moment, nearly three years ago, when Washington and Havana announced they would reestablish diplomatic relations after a lapse of more than five decades, a move that led to budding tourist and commercial trade between the two.

What’s even more startling: Nobody seems to be able to explain what happened. The United States says that over the past 11 months, 22 of its diplomats have been the victims of invisible attacks that left them nauseous, dizzy and with splitting headaches. (At least five Canadian diplomats in Havana have reported several similar symptoms.) Some of the attacks were accompanied by buzzing or thumping sounds; some were silent.

Cuba says it neither committed the attacks nor knows anything about them. And, to the surprise of many, Raúl Castro’s government permitted FBI agents to enter the country to help investigate.

But if the investigation — which began in February, when the State Department decided there was a pattern to ailments reported by its diplomats — has turned up anything, it hasn’t been disclosed — even within the U.S. government itself.

Intelligence-community experts told one of the congressional intelligence committees in a recent classified briefing that they aren’t even sure about the device involved in the attacks. Their testimony reflects just how little is understood about the technology being used, said one congressional staffer. It could be either ultrasound, infrared or even x-ray, lawmakers were told.

That the United States, with its vast investment in high-tech — both government and private — apparently can’t even venture a guess about what sort of technology is being employed in the attacks is befuddling to many observers.

“It absolutely is mysterious,” said retired CIA analyst Brian Latell, the agency’s former national intelligence officer for Latin America, now an adjunct professor at Florida International University’s Jack D. Gordon Institute for Public Policy.

A retired diplomat with extensive experience in Latin America went even further. “If we say we can’t identify it, it’s probably because we have one of our own,” he said. “And we’re not going to let them know we know anything about it.”

Speculation abounds, from the use of ultrasonic waves to the possibility that nothing happened at all and the diplomats fell victim to mass hysteria.

Acoustic weapons do exist. Many private ships use something called a Long Range Acoustic Device to drive off Somali pirates in the Gulf of Aden. “It produces this terrible, ear-shattering noise that nobody can stand,” said one former security official.

Moreover, Cuba has a history of using loud sounds to harass American diplomats. When former foreign service officer (and, more recently, former Coral Gables mayor) James Cason was the chief U.S. diplomat in Havana from 2002 to 2005, the Cuban government sometimes put giant speakers in front of the building that now serves as the embassy three times a day and blasted the same song, over and over, for an hour.

“There really wasn’t anything we could do about it,” Cason remembers. “I told all the guys to call their wives at home and say, ‘Hey, I really love this song they’re playing, could you go out and buy a copy?’ Just to annoy the Cuban intelligence guys we knew were listening to our calls.”

The problem with the acoustic-weapons theory is that, like those speakers pounding the embassy, they’re mostly large and all extremely loud. They couldn’t be used without attracting widespread notice, especially at diplomatic residences festooned with video surveillance cameras.

But Cold War history offers at least another intriguing possibility: microwaves. In the 1970s, the Soviet Union bombarded the U.S. embassy in Moscow with microwave signals, either trying to steal American secrets or stop Americans from stealing Russian secrets, it was never clear which.

Bits and pieces of the story emerged at the time, but the first comprehensive account appeared last year in journalist-historian Fred Kaplan’s book “Dark Territory: The Secret History Of Cyber War.” The story began, Kaplan wrote, in the mid-1970s, when the Soviet Union changed its communication system from radio to microwave transmissions in an attempt to undercut American spying.

Radio waves bounce around a lot and are relatively easy to steal. But microwave transmissions can only be intercepted by receivers directly in their line of sight. The U.S. National Security Agency promptly put a listening station on the 10th floor of the American Embassy in Moscow, where it could even listen in on phone calls made by Soviet leader Leonid Brezhnev from his limousine.

The listening center was so important to U.S. intelligence that, when a fire broke out in the embassy and the Moscow fire department said it needed access to the 10th floor to put it out, NSA chief Bobby Ray Inman told State Department officials, “Let it burn.”

The Russians, eventually, caught on and retaliated by aiming microwave barrages directly at the listening post. Whether they were trying to listen in on conversations inside the room (microwaves can be used to pick up sounds bouncing off glass) or simply hoping to screw up the American spying operation was never established.

But there was a side effect: Some U.S. diplomats exposed to the Soviet microwaves became ill. And though it never leaked into mainstream media, a low-key debate in medical journals continued for years about whether microwaves caused the illness.

Mark Elwood, a professor of cancer epidemiology at the University of Auckland in New Zealand and author of a 2012 academic paper on the debate, has been following news reports about the Havana attacks closely.

“It is intriguing,” he told the Miami Herald on Tuesday, “although I have not seen any real evidence that this is a real issue and not just minor reported illnesses.”

Historian Kaplan doesn’t believe the Soviets were intentionally trying to injure American diplomats. “The microwave beams may have had the effect of weapons,” he told the Herald. “But they were beamed for intel purposes.”

And, he added, it’s entirely possible that the entire Moscow scenario is being repeated in Havana: Cuba using leftover Russian technology of the 1970s to transmit secrets. The United States using 1970s techniques to steal them. And Cuba retaliating just as the Russians did.

El Nuevo Herald staffer Nora Gámez Torres contributed to this report.

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