The U.S. sent warships speeding to the scene. But they were hours away when the brazen pirates attacked, and the world's greatest sea power had to face the fact that it had only limited options to respond to the startling seizure of American merchant seamen.

The outcome for the U.S.-flagged Maersk Alabama and its crew was still unclear as Wednesday night turned into Thursday morning off the coast of Somalia. The crew had retaken control of the cargo ship from a band of pirates, but the captain was still held by the attackers in one of the ship's lifeboats.

The limits of U.S. power are a hard reality facing the Obama administration, which has so far done no better than its predecessor to thwart the growing threat of piracy along a huge, lawless stretch of African coastline.

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President Barack Obama had no public comment but was closely following the pirate-hostage drama, the first like this in modern history involving a U.S. crew, said Denis McDonough, a senior foreign policy adviser at the White House.

"We have watched with alarm the increasing threat of piracy," McDonough said. "The administration has an intense interest in the security of navigation."

An American Navy destroyer, the USS Bainbridge, arrived off the coast of Somalia a few hours before daybreak, Kevin Speers, a spokesman for the cargo ship's owner, told AP Radio. U.S. officials said earlier that the Bainbridge and at least six other vessels were headed to the area.

Pentagon spokesman Bryan Whitman would not confirm that the Bainbridge had arrived, saying he could not discuss any ongoing operations.

The Bainbridge was among several U.S. ships, including the cruiser USS Gettysburg, that had been patrolling in the region. But they were about 345 miles and several hours away when the Maersk Alabama was seized, officials said.

The Bainbridge is a guided missile destroyer carrying Tomahawk cruise missiles, torpedoes and two MH-60 Knighthawk helicopters armed with Hellfire missiles.

It was not clear what the military crews would do when they got to the scene. Options could include negotiation, backed by the threat of force. Any military action could risk the lives of the Americans, especially the captain being held hostage. Last Sept. 15, however, helicopter-borne French commandos swooped in to rescue two French citizens taken captive by Somali pirates aboard a luxury yacht.

Operations would probably include watching the ship via helicopters and unmanned aircraft overhead, as well as ships in the surrounding waters, including the pirates' boat. In the past, surveillance aircraft, including unmanned drones, have flown over captured vessels to take photos and collect other information.

The Bainbridge carries with it the ScanEagle, a 40-pound drone with night vision. It can fly as high as 16,000 feet and linger over a target for more than 20 hours. The Navy used a ScanEagle aboard another ship to detect a suspicious small boat in February. Nine suspected pirates were captured.

Despite America's technical and firepower edge, there is too much ocean to cover, and too many commercial vessels to protect, for full-time patrols or escorts for threatened ships.

U.S. legal authority is limited, too, even in the Maersk Alabama's case of American hostages and a cargo of donated American food. Somali pirates, emboldened by fat ransoms, have little reason to fear capture.

"The military component here is always going to be marginal," said Peter Chalk, an expert on maritime national security at the private Rand Corp.

According to the Navy, it would take 61 ships to control the shipping route in the Gulf of Aden, which is just a fraction of the 1.1 million square miles where the pirates have operated. A U.S.-backed international anti-piracy coalition currently has 12 to 16 ships patrolling the region at any one time.

Along the Somali coastline, an area roughly as long as the eastern seaboard of the United States, pirate crews have successfully held commercial ships hostage for days or weeks until they are ransomed. In the past week, pressured by naval actions off Somalia, the pirates have shifted their operations farther out into the Indian Ocean, expanding the crisis.

Oceans of that immense size cannot be patrolled completely, even with high-tech detection equipment doing some of the work.

"Wherever the police are, the robbers will go somewhere else," Chalk said.

There are also legal questions about where and how to prosecute pirates, and about how far the U.S. military can or should go to help or protect commercial ships.

In December, alarmed by increases in hijacking incidents, the Bush administration sought and won U.N. Security Council authorization to expand international naval operations against Somali pirates to allow the pursuit of suspects on the ground in Somalia.

The move, which came at a special session attended by Secretary of State Condoleezza Rice and other foreign ministers, was the fourth taken by the council in the second half of 2008 alone to combat the pirates.

Three months into the international anti-piracy campaign, as many as 17 nations are participating in increased patrols, and more are expected to join.

But U.S. defense officials say the only realistic solution is on shore in Somalia, where money from the piracy ransoms fuels militant activities in the largely lawless country.

Navy officials have urged patience, saying the key will be to watch for progress over the next year to see if the increased patrols and agreements for piracy prosecutions begin to work.

Vice Adm. Bill Gortney, commander of the U.S. Navy's 5th Fleet, told the House Armed Services Committee that the Pentagon is looking at the issue of ordering strikes inside Somalia and said that, "ultimately, the solution to the problem of piracy is ashore — in Somalia."