I seem to remember that the British Navy, and the US Navy maybe, used to give out a ration of alcohol to sailors each day. When did this practice stop, and why?
In the United States, alcohol rationing was stopped in 1862 by an act of Congress which also prohibited "distilled liquors" from being aboard a vessel, with an exception made for medical supplies. Then Secretary of the Navy Gideon Welles issued a general order requiring captains to comply.
Two years later, Welles issued another general order requiring that all beer and wine and other non-distilled liquors be treated as the private stores of seamen, and required them to be stowed securely in private areas (Lockers, etc). He further specified that each sailor needed permission from their captain in order to bring it aboard.
In 1893 Article 1080 of the Navy Regulations permitted wardroom and steerage officers to form their own wine messes, that is a mess area for wine. No officers were required to be members of the wine mess.
Finally in 1914, Josephus Daniels, who was the Secretary of the Navy then, issued a general order prohibiting all consumption of alcoholic beverages on-board all Navy vessels.
One reason this practice was discontinued was there was no longer a need for the alcohol. Originally it was used to sweeten stale water that had grown algae in it after a long voyage, and modern storage methods precluded the need for this. Another reason it was discontinued in the US was changing attitudes about alcohol.
In the UK, the beverage issued was called grog, named either for how you'd feel when you drank it (groggy), or maybe more likely, named after the Admiral who instituted the practice of using Rum, "Old Groggy". The practice continued until 1970 among British sailors.