The Navy knows how a fire started aboard the USS Miami, but two panels are continuing their wide-ranging investigations. The Navy aims to complete the dual probes by the Fleet Forces Command and Naval Sea Systems Command by month’s end. The panels are looking at factors that contributed to the fire’s rapid spread as well as ways to reduce hazards and improve firefighting response. While in dry dock at Portsmouth Naval Shipyard, the Los Angeles-class attack submarine suffered $450 million worth of damage from the fire that the Navy says was set by a civilian worker in May. The Navy intends to repair the submarine, which is based in Groton, Conn., and return it to the fleet in 2015.