Four persons arrested in Los Angeles are part of a Chinese intelligence-gathering ring, federal investigators said, and the suspects caused serious compromises for 15 years to major U.S. weapons systems, including submarines and warships. U.S. intelligence and security officials said the case remains under investigation but that it could prove to be among the most damaging spy cases since the 1985 one of John A. Walker Jr., who passed Navy communication codes to Moscow for 22 years. The Los Angeles spy ring has operated since 1990 and has funneled technology and military secrets to China in the form of documents...