The U.S. Navy believes that Monday's incident was the first time the American-made 20mm Phalanx weapons system accidentally shot down a friendly aircraft.

One Japanese official believes mechanical trouble caused the accident, in which a plane towing a target drone three miles behind it was blasted out of the sky by a Japanese destroyer. The pilot and his bombardier escaped with minor injuries.

Carol Royster, wife of downed pilot
Lt. Cmdr. William Royster

Apparently, the projectiles "were launched when they weren't meant to be," said Tensuke Kobayashi, a Japanese navy official.

Cmdr. Keith Arterburn, Navy spokesman, said he couldn't comment on the statement by the Japanese official.

At the Pentagon, Navy Capt. Michael Doubleday said that under normal procedures a ship would be in communication with the plane towing a target drone. He said he did not know if procedure was followed in this case.

Doubleday said yesterday that the downing was the first such accident he knew of in the 25 years those war games have taken place.

Lt. Cmdr. Richard Marin said in an interview from Hawaii, headquarters of the Pacific Fleet, that most RIMPAC activity does not use live ammunition.

The cause of the downing of the 26-year-old A-6E Intruder 1,600 miles west of Hawaii Monday, as well as possible reparations by the Japanese government will be part of the Navy investigation, Arterburn said.

The State Department yesterday said, however, it doubted the United States would seek compensation from Japan for the loss of the jet.

Separate investigations are being conducted by the Japan Maritime Self Defense Force and the Navy's 7th Fleet.

Until they are completed the Navy has temporarily suspended live fire gunnery exercises between Japanese and U.S. Navy vessels while both sides review their safety procedures.

Japan has apologized for the incident, in which its destroyer, Yuugiri, fired and hit the Intruder as it towed a target drone.

The American-made weapons system, which was manufactured by General Dynamics in Pomona, Calif., hit the plane, forcing its two crew members to eject.

The pilot, Lt. Cmdr. William Royster of Kansas City, Mo., and bombardier-navigator, Lt. Keith Douglas of Birmingham, Ala., were rescued within minutes by the Yuugiri.

The minor injuries sustained by the two Navy pilots were attributed to problems caused when they ejected from the jet.

The violent, high-speed ejection from the cockpit "almost took his nose off," Royster's wife, Carol, said. "They had to sew part of it back on."

Douglas was treated for superficial abrasions and returned to duty.