Each year, the imaginary nation of Berylia is summoned into existence solely to have its simulated computer networks pummeled by an elite team of hackers.

But the Berylians are not left undefended in the face of the onslaught.

A NATO-backed center in Estonia invites military teams from across the alliance to come to its aid — and next week a small detachment of Maryland National Guard airmen will help staff the digital ramparts.

Maryland National Guard Col. Charles S. Kohler, who has been helping to plan the exercise, has had a look behind the scenes. The defending teams should expect to be pushed to their limits, he said: “It's not designed to be easy.”

It's the first time troops from the Maryland National Guard will be involved in the exercise, the largest of its kind in the world.

Their participation is part of the Guard's larger effort to expand its ability to fight in cyberspace, the emerging fifth domain of warfare, beyond land, sea, air and space.

The Guard is ramping up new units, planning a pair of major building projects and figuring out how to work with other agencies in the face of a hack.

The Defense Department is moving quickly to train thousands of troops to fight battles on computer networks.

Commanders envision a major role for the National Guard, which has members who bring cutting-edge skills from their full-time careers, along with the ability to be deployed more easily than regular troops to respond quickly to hacks against civilian targets.

“These are the people who are probably working in the security space already by day,” said Richard Forno, the director of the graduate cybersecurity program at the University of Maryland, Baltimore County. “When the balloon goes up, they can lend assistance, they're trained, they're component.”

Just as the National Guard has been ready to respond to major snowstorms and civil disturbances, it now has contingency plans for major cyber incidents.

One scenario envisioned by analysts involves an attack on the power grid that leaves customers without power for days, but less dramatic hacks still could overwhelm the ability of public agencies or businesses to respond.

During the unrest last year that followed the death of Freddie Gray, guardsmen were deployed to make sure state computer networks stayed up and running.

Guard units in other states have demonstrated how they can be of assistance before a crisis.

Last year, Washington State guardsmen helped a public utility figure out where it had weaknesses in its computer networks.

Kohler said Maryland, which is home to the National Security Agency, U.S. Cyber Command and a sizable private cybersecurity industry, is especially well positioned to take on a bigger role.

“You have a tremendous amount of need in this area for these types of people who work in this field,” he said. “Maryland is just a natural fit.”

The Maryland Air National Guard now has 300 personnel assigned to four squadrons in the 175th Network Warfare Group.

To accommodate the growth, the Guard is planning to build a $4 million facility on Fort Meade and a $13 million building at its air base in Middle River.

The aim is to have troops trained and ready to keep enemy hackers out of the military's networks — or to at least keep computers working as they come under attack — and to respond in kind.

The Defense Department announced this year for the first time that it was launching cyber attacks in the midst of a conflict, using digital weapons to attack the computer systems of Islamic State terrorists in Iraq and Syria.

While the world has yet to see a full-scale cyber conflict, a battle for dominance online is widely expected to be part of any future war.

It's that kind of scenario that will play out in the Estonia exercise, which is run by the NATO Cooperative Cyber Defence Centre of Excellence in Tallinn.

Called Locked Shields, it's expected to involve some 550 participants this year.

The Maryland airmen are to be embedded with an Estonian team, one of twenty charged with defending Berylia's networks.

Those teams will battle the attacking force for a week, facing close to 2,000 attacks, the organizers say.

They'll have to consider questions they would face in a real operation — such as how much information to give to regular Internet users who are noticing interruptions in their service.

Tallinn, with its medieval walls and picturesque old town, might seem an odd choice for a center dedicated to the newest form of warfare.

But Estonia was quick to embrace the Internet.

The Maryland National Guard has long-standing ties with Estonia under a Defense Department program designed to bolster the militaries of former Soviet republics. With Maryland emerging as the home of the United States' cyber efforts, the two have followed a similar path.

Maj. Gen. Linda Singh, the head of the Maryland Guard, now wants to bring a version of the center of excellence home with her.

The idea, Kohler said, is to coordinate among the government, businesses and universities that teach cybersecurity courses.

Doug Mayer, a spokesman for Gov. Larry Hogan, said the administration supports the effort.

The center could help ensure a pipeline of workers with the skills to defend computer networks and, enable the state to better coordinate its response when a major institution or piece of infrastructure comes under attack.

“We want to make sure we're all pulling in the same direction,” Kohler said.