The Groton-based USS Providence crossed the Suez Canal Saturday and headed for the Mediterranean Sea, where other Navy ships are waiting to respond to the violence in Libya if needed.

Submarines are uniquely suited for gathering intelligence on Libyan leader Moammar Gadhafi's attacks on the opposition, according to Loren B. Thompson, chief operating officer at the nonprofit think tank, Lexington Institute.

"Submarines are so stealthy, they can collect intelligence that other means cannot," Thompson said Tuesday. "And having a ship like the Providence nearby makes a big difference in terms of understanding what's actually happening in the area."

A Navy spokesman confirmed Tuesday the route of the Providence (SSN 719) into the Mediterranean Sea, but said he could not discuss the details or assets being directed toward Libya, particularly submarines.

The USS Kearsarge, the USS Ponce and the USS Barry are in the Mediterranean. A destroyer, the USS Mason, also crossed the canal with the Providence, the spokesman said. The Los Angeles-class submarine traveled with the USS Enterprise carrier strike group.

"It's not the number or type of ships that matter just yet as much as the missions they are assigned," said Peter W. Singer, director of the 21st Century Defense Initiative and a senior fellow in foreign policy at the Brookings Institution. "And as of yet, that exact mission doesn't seem to have been decided by the U.S. and international leadership on the political side."

The Navy ships could be used for anything from mere presence patrols to enforcement of a no-fly zone or blockade, Singer added.

Tuesday, the foreign ministers for the eight most powerful industrialized nations met but could not agree on a no-fly zone or any other military operation. Thompson cautioned that the buildup of Navy assets is unlikely to significantly influence the conflict without the establishment of a no-fly zone, since without one "it's obvious we're not going to do anything more ambitious."

It would take a "major military provocation" by Gadhafi to elicit a U.S. response, in which case submarines could be used to fire missiles, intercept electronic messages between Gadhafi and his military personnel or send special operations forces ashore, Thompson said.

In 2003, the Providence fired missiles into Iraq from the Red Sea. Eighteen months earlier, the sub had fired some of the opening shots against the Taliban regime in Afghanistan.

The submarine was built at Electric Boat and delivered to the Navy in 1985.