Two U.S. Navy sailors have been arrested on charges of providing sensitive U.S. military information to China in exchange for money in what the Justice Department called a relentless effort by China to get U.S. secrets.

Jinchao Wei was the first person ever charged with espionage in the San Diego district, U.S. Justice Department officials said at a news conference. Petty Officer Wenheng Zhao, 26, of Monterey Park, California, was charged with conspiracy and receipt of a bribe by a public official in Los Angeles.

Both men are Chinese-born naturalized U.S. citizens. It wasn’t immediately clear whether they have retained lawyers.