Seamen of the British Royal Navy were entitled to rum

Since the 17th century, Royal Navy sailors had been entitled to a gallon (then just under four litres) of beer a day. Beer lasted longer on board than drinking water, but also had a limited shelf life.

On longer voyages and in warmer climates, people therefore resorted to brandy. After the British conquest of Jamaica in 1655, brandy was increasingly replaced by rum, which was cheaper and easier to obtain and even improved in quality when stored in wooden barrels on board.

From 1731 onwards, rum was part of the official shipboard catering. Half a pint (about a quarter of a litre) of rum, spread over two issues per day, was the equivalent of the daily gallon of beer. British Admiral Edward Vernon had the rum served only diluted with water, one part rum to four parts water. Vernon's nickname among the sailors, "Old Grog", is said to have given the mixture of rum and water its name.

In 1824 the ration was reduced to half and from 1848 crewmen could choose between rum and tea with sugar. In the course of the following years, the rum ration was reduced more and more or abolished altogether for some service guards, so that by 1950 only about a third of British naval personnel received the daily rum ration.

A British newspaper finally pointed out that naval personnel were not even allowed to drive a car after receiving their daily rum ration, but here they were on duty on warships. And so Black Tot Day came on 31 July 1970 and official rum rations were history.