NAIROBI, Kenya — The small gang of Somali pirates fired on an approaching ship, hoping their midnight attack would bring them millions in ransom. The ragtag bandits, though, had taken on far more than they could handle: a U.S. warship.

The USS Nicholas, a guided missile frigate, was tracking the pirates when they opened fire early Thursday in Indian Ocean waters, the U.S. military said.

The Nicholas, which saw combat in the first Gulf War, returned fire and disabled the skiff.

Navy personnel later boarded and detained three suspects. The Americans found two more bandits on a nearby mothership and later sank the skiff.

It was not the first attack against a Navy ship, but it underscored the fact that most pirates aren’t terribly sophisticated, said Roger Middleton, a piracy expert at the British think tank Chatham House.

“If you think of the kind of young men who are doing this, they go out into the middle of the ocean in a tiny boat. They might not always make rational decisions, and they often attack things that are bigger than they should (attack),” said Middleton.

“It’s also quite possible that they don’t have a full understanding of the targets they are attacking.

“Perhaps they just see a big ship they think is a worth a lot of money,” he said.

International naval forces have stepped up their enforcement of the waters off East Africa in an effort to thwart a growing pirate trade.

Thursday’s attack took place between the coast of Kenya and the island nation of Seychelles, said Navy Lt. Patrick Foughty, a spokesman.

The U.S. Africa Command said the five pirates seized Thursday would remain in U.S. custody on board the frigate for now.