Two people assisting oceanographic research for the U.S. Navy were killed Wednesday when a depth charge exploded on the deck of a civilian research ship off the coast, Coast Guard and Navy officials said.

The blast occurred 20 miles west of the mouth of Grays Harbor aboard the Amy Chouest, on a 250-foot research ship operated by the Applied Physics Laboratory of Johns Hopkins University in Baltimore, Md., said Lt. Cmdr. Scott Wilson of the Trident submarine base at Bangor, Wash.Wilson said the ship was not seriously damaged and was in no danger of sinking following the 10 a.m. explosion.

The names of the victims were not immediately available.

"They were scientists or members of the crew who were engaged in setting these devices and dropping them overboard and somewhere in the course of this there was a premature detonation," Wilson said.

He said the cause of the explosion would be investigated thoroughly.

No other crew members were injured.

Wilson said the explosives were Mark 61 depth charges, each packing 1.8 pounds of TNT. He said the charges are exploded under water at various depths and are detected with accoustic sound reading devices.

He would not further specify the purpose of the mission.

However, Trident submarines may have been involved, as the Navy's initial reports of the incident emphasized that no subs had fired on the ship or had surfaced underneath it.

The Coast Guard sent two helicopters and a cutter to the scene and brought in Navy explosives experts who secured the remaining explosives on the deck, said Coast Guard Lt. Don Dyer.