The captain gave the order, and the sailor replied, 'Aye aye, sir.'
aye aye, sir
idiomThe correct and seamanlike reply, onboard a Royal Navy and US Navy ship, on receipt of an order from someone of senior rank or authority. It means "I understand the command and hasten to comply with the order."
When the commander told him to secure the rigging, the young deckhand shouted, 'Aye aye, sir,' and ran to obey.
Though unaccustomed to naval discipline, the midshipman snapped to attention and barked, 'Aye aye, sir,' masking his fear with a crisp salute.