Possible Clues:

• Essential part of service in lower part of ship
• Unpopped popcorn piece
• Heart of a nut
• We hear an officer that's at the heart of things
• Navy breaking up part of ship, in essence
• In essence, reading to Pole in lower part of ship
• Corn piece
• Corny bit
• Orville Redenbacher's unit
• Part of ship in which sailors stored grain