Group Sues to Block Navy Sonar By COLLEEN VALLES Associated Press Writer SAN FRANCISCO (AP) — Environmentalists have taken aim at a powerful low-frequency sonar system used by the U.S. Navy, which they say can strand, or even kill, marine mammals. A coalition of environmental groups led by the Natural Resources Defense Council sued the Navy and the National Marine Fisheries Service in federal court Wednesday to block the use of the system, which identifies enemy submarines. The groups say the sonar can interfere with marine mammals' communication systems. In July, the fisheries service, a division of the National Oceanic...