MUMBAI: The Indian Navy suffered a huge blow Wednesday when a front line submarine exploded and sank here at dawn with 18 sailors after two explosions turned it into a deadly ball of fire. The same submarine was hit by an explosion in 2010 that killed one sailor and injured two others. The navy said that accident was due to a faulty battery valve that leaked hydrogen, causing an explosion in the battery compartment. There have been no details on what caused this week's blasts.