NORFOLK, Va. (AP) — A ceremony paid tribute to 47 sailors who were killed when a gun turret exploded on the USS Iowa in 1989.

The ceremony was held Friday on Naval Station Norfolk to mark the 30th anniversary of the explosion on the Norfolk-based battleship on April 19, 1989.

The ship’s Number Two turret exploded during a gunnery exercise off the coast of Puerto Rico.

The Navy initially claimed the explosion was a result of a suicidal attack by a ship petty officer. A congressional investigation found the explosion was likely caused by guns being over-rammed with powder.

After re-opening its investigation, the Navy concluded that the cause could not be determined.