GUANTANAMO BAY NAVY BASE, Cuba -- The boatpeople trying to reach U.S. soil are imaginary and so is the Caribbean nation in crisis. But the Army general who flew in from Texas to take charge is the real deal for hundreds of troops rehearsing to get ready for a humanitarian crisis.

Guantánamo’s airstrip was abuzz this weekend as about 500 troops descended for an every-other-year drill whose name reflects how little the military wants to draw attention to it — Exercise Integrated Advance.

For a week, soldiers, sailors and Homeland Security officials are rehearsing how to manage an imaginary humanitarian-relief crisis inspired by the tens of thousands of Haitians and Cubans who overwhelmed this base in the 1990s.

But the exact nature of the scenario — how many migrants flood the base, whether there’s unrest, disease, spies in the tent camps — is all classified. Only Pentagon-approved photos of the exercise will be released, and the people involved in acting out the episode from here to Miami to Washington, D.C., are sworn to secrecy.

That’s because nobody wants news about it to touch off a real, live Caribbean exodus. The intent, say organizers, is not to encourage anyone in the Caribbean to get on rafts to reach this Navy base in southeast Cuba, but to be ready in case it happens.

Is the scenario driven by political unrest or a natural disaster?

All Army Col. Greg Julian, spokesman for the U.S. Southern Command, will say is that this 21st century war-game is about a “mass migration event in the Caribbean.”

One thing they’ll rehearse is registering 1,000 migrants in a single day. And if history is any guide, the actors should cram inside the processing tent — desperate, undocumented and disorganized.

“We certainly wouldn’t want to instigate a real event,” said Julian from Southcom, which is spending $2.7 million on the exercise, nearly half of it on transportation for troops and supplies from its Army South headquarters in San Antonio, Texas.

So, “We generally won’t use a nation. We use ‘country 1,’ ‘country 2’ because we don’t want to get into any political issues.”

The exercise is occurring less than a month after Cuba abandoned a policy of requiring citizens to get exit visas to leave the island legally.

But so far, the U.S. government has detected “no spike or anything” of Cubans trying to reach U.S. soil either by land or sea, said a federal official who spoke on condition he not be named because he was not authorized to discuss the Pentagon’s drill.

The drill was planned long before Cuba changed its exit-visa policy, with U.S. government divisions that would answer to the Department of Homeland Security rehearsing a reaction to “whatever that push factor is going to be,” from “political activity” to “natural disaster.”

“It helps us to make sure all the ducks are in a row,” Julian added, “if and when we have to kick this off for real.”

The International Organization for Migration is taking part; the International Committee of the Red Cross is not.

Meantime, just to make sure there’s no misunderstandings, the Navy captain in charge of the base here used the occasion of his monthly meeting with a Cuban Army officer at the U.S. Marine Corps fence line to notify the military across the minefield of the reason for the U.S. troop build-up.