They attacked in waves, breaching several layers of security in an attempt to corrupt a nation's computer network.
Two, three, five times per day, the computer hackers tried to get in. And each time the Naval Academy's midshipmen withstood the challenge.
But they remained tense as the clock wound down Friday, since their opponents were more than formidable: They were the technical wizards of the National Security Agency.
"The biggest surprise is that there haven't been any surprises yet," said Midshipman Ryan W. Collins-Minkel of Tampa, Fla.
The Cyber Defense Exercise, conceived by an NSA official seven years ago, pits teams of future military officers against each other to see who can build and maintain the most secure computer network.
The task has immediate applications, since it mirrors the goal of the Department of Defense's Global Information Grid Vision, which calls for the military to operate a secure, high-speed network that improves the ability of the joint military services to work together.
"The skills they are learning here are absolutely essential," said Capt. Thomas A. Logue, associate chair of the academy's computer science department. "It's not just about providing [information technology] service. It [hacking] has become a warfare component in its own right."
Preparing for the exercise took months of preparation and hundreds of pages of paperwork, culminating in a weeklong exercise filled with long hours of monitoring the network's security, efficiency and reliability.
To prepare for the competition, the academy team's 50 members developed an organization structure last fall similar to that of a military operation in the field.
Tasks were delegated. Senior team members were put in supervisory roles. A rotating schedule was implemented, with more Mids called in when needed.
The ideal result: a well-oiled machine that analyzes intelligence reports, responds to threats as they come and makes sense of it all later in detailed reports for Meridia, a made-up island nation with an unstable government and a terrorist element.
"We're seeing a lot of [these assignments] in Iraq and Afghanistan," Midshipman Gregory Mischler said. "Most everyone in this room will be in a management role, and this is the kind of thing [the Navy] will have us doing."
The competition was set up with each team beginning with 50,000 points, said Midshipman Justin D. Norman, who monitored the network for suspicious activity. NSA officials, who judged the exercise, could deduct points for errors such as hardware being down at the wrong time and teams falling for traps, such as opening e-mail sent by hackers.
"A lot of the problems we have are actually normal wear-and-tear use," Norman said. "We really have to make sure that when something goes down, we get it back up to service as soon as possible, or we lose points."
From Monday to Friday, NSA hackers repeatedly attempted to sabotage the network with a variety of methods, most available online.
"The tools they used are written well enough where any well-educated 12-year-old could use them," said Mischler, commander of the Naval Academy team. "It's a scary thought."