SAN DIEGO (AP) — Twenty-one people have suffered minor injuries in an explosion and fire Sunday on board a ship at Naval Base San Diego. The blaze was called in shortly before 9 a.m. on the USS Bonhomme Richard. The cause is under investigation. Officials don’t immediately know where on the 840-foot amphibious assault vessel the fire was sparked. San Diego is the Bonhomme Richard’s home port, and it was undergoing routine maintenance at the time of the fire. Officials said about 160 sailors and officers were on board — far fewer than the thousand typically on the ship when it’s on active duty.