Old Naval Drink is a term used to describe a beverage that was served to sailors in the British Royal Navy during the 18th century. The drink was known as GROG, which is a combination of rum, water, and lime juice. It was given to sailors to help prevent scurvy, a disease caused by a lack of vitamin C. GROG was also believed to improve morale among sailors, and it was served on board ships until 1970.