A federal appeals court ruled Wednesday on the legal definition of piracy, saying an armed attack on a U.S. vessel can be considered piracy even if no one ever boards or robs the ship.

The 200-year-old U.S. Supreme Court definition of piracy has been in dispute in two attacks on Virginia-based Navy ships in April 2010 in waters off East Africa. The defendants were prosecuted in Norfolk, the first in a series of government prosecutions aimed at slowing the spread of piracy off Africa.

The court's ruling gives prosecutors wider latitude to go after people who attack U.S. vessels, U.S. Attorney Neil MacBride said.

"For decades, the international community has considered violent attacks on the high seas as an act of piracy, and today's ruling will strengthen our ability to hold those who attack U.S. vessels by force accountable, regardless of whether they are successful or not," said MacBride, whose office handled both cases.

In one case, a lower court judge dismissed charges against five Somalis in an attack on the USS Ashland, ruling since the men had not taken control or robbed the ship their actions did not rise to the definition of piracy. The ruling sends that case back to U.S. District Court for trial, the government said.