NEW : Shots fired in escape attempt , captain apparently tied up , military officials say . Comment: Captain 's escape attempt viewed as `` optimistic sign '' of his vitality . Richard Phillips , captain of a U.S.-flagged cargo ship , is being held by four gunmen .
NEW : Shots fired in escape attempt , captain apparently tied up , military officials say . Pirates using other hijacked ships to look for lifeboat as Navy ships arrive . Captain 's escape attempt viewed as `` optimistic sign '' of his vitality . Richard Phillips , captain of a U.S.-flagged cargo ship , is being held by four gunmen .