Possible Clues:

• Essential part of service in lower part of ship
• Essence of an idea
• Central or most important part
• Unpopped popcorn piece
• We hear an officer that's at the heart of things
• Back end of lough and lake, in essence
• Navy breaking up part of ship, in essence
• Most important part of fleet in base
• In essence, reading to Pole in lower part of ship
• Corny bit