NAIROBI, Kenya—The U.S. employed them during World War II: armed convoys on the high seas to protect Allied shipping lanes from German subs. Could the same work with pirates?

Some maritime experts say escorting the more than 20,000 ships that transit the Horn of Africa every year would be impractical, outstripping available military resources and at a cost that would be too high. But the tactic is being revisited, and NATO is considering it.

“It’s true that it’s more expensive to convoy, but it’s worth the money,” said Peter D. Zimmerman, an American professor emeritus at King’s College in London. “There is a clear and present danger, and it’s extremely corrosive to the maritime system to allow these pirates to operate with impunity.”

The Gulf of Aden, which links the Suez Canal and the Red Sea to the Indian Ocean, is the shortest route from Asia to Europe. It’s one of the world’s busiest shipping lanes, and these days among its most dangerous.

Piracy is skyrocketing in the region and at least 79 attacks have been reported this year, compared with only 21 in all of 2003, according to the International Maritime Bureau. Pirates are now holding more than 280 foreign crewmen on 15 ships—at least 76 of those sailors captured in recent days.

The crisis has spawned fresh debate on how to stop it, but options are slim. Commercial vessels are loathe to travel with armed security aboard because they fear violence could escalate. And in many cases, they have no choice since carrying arms is illegal in many ports.

During World War II, Allied warships deployed to protect merchant vessels crossing the Atlantic after Nazi submarines began sinking them with impunity. Today, the threat is different with modern-day warships facing lightly armed, agile pirate skiffs that are not trying to destroy vessels, but seize them for ransom.

Cyrus Mody, of the International Maritime Bureau, said there are only 15 to 20 warships deployed in the Gulf of Aden and off Somalia’s eastern coast at any one time —a fraction of what is needed to guard tens of thousands of ships, even in convoys.

At the Pentagon, officials dismiss the use of convoys, partly because of the high number of personnel such a mission would entail. Also, the military has been adamant that ship security be the responsibility of shipping companies.

One senior defense official said privately that it would be impossible, with the number of U.S. and coalition ships available, to both escort convoys and patrol the gulf at the same time.