It seems the Admiral wasn't expecting a fight. All it takes is maneuvering him into a situation where you can kill him without his notice, and he's dead. You open the door to his office, planning a judicious flight, and run directly into a man whose credentials reveal him as one Lieutenant Horatio Laine of Stormwind. "Don't make any moves, kid," he says. "If you have the information, spill it."
Acquiesce. Ask for more information. Dodge past him and leave. Threaten Laine back.