The Navy sank a second ship during a live-fire exercise at sea Tuesday as the Rim of the Pacific international naval exercises continued in Hawaii waters.

The decommissioned 44-year-old cargo ship Concord was used as target practice 61 miles northwest of Kauai at 4:12 p.m. Tuesday. On Friday, Navy and allied ships and aircraft sunk a decommissioned cargo vessel — the Niagara Falls — 63 miles northwest of Kauai.

One other decommissioned vessel, the former USS Kilauea, will be sunk during RIMPAC training.

The Navy said the sinkings provide "the opportunity to gain proficiency in tactics, targeting and live firing against surface targets … "

Environmental groups Basel Action Network, Sierra Club, Earthjustice and Center for Biological Diversity have condemned the Navy’s ship-sinking exercise.

The Navy said it follows EPA regulations and that the target practice takes place at least 57 miles from land and in water at least 6,000 feet deep.