For hundreds of years, Royal Navy seamen lined up in galleys from the poles to the tropics to receive their regulation lunchtime tot (about eighth to half pint) of rum, but 40 years ago, the tradition was ended. On 31 July 1970, known in the navy as Black Tot Day, free rum was retired from navy life.
By 1970, the rum bosun's daily doling out of of rum at midday, diluted with water (grog) for junior ratings, neat for senior - was a reasonably gentlemanly affair. A grog was a mixture of two pints water and a half pint rum. The Admiralty took away the rum because it was concerned it would hinder sailors' ability to operate increasingly complex weapons systems and navigational tools.
Beer had been the staple beverage of the Royal Navy until the 17th Century, used as a self-preserving replacement for water, which became undrinkable when kept in casks for long periods. As the horizons of the British Empire expanded, the sheer bulk of beer, the ration for which was a gallon per day per seaman, and its liability to go sour in warmer climates, made it impractical to take on long voyages. Wine and spirits started to take the place of beer place until 1655, after the capture of the island of Jamaica from Spain, the navy introduced rum.
Until 1740 the daily ration was half a pint of neat rum, twice a day. Sailors would check their rum had not been watered down by pouring it onto gunpowder and setting light to it, from where the term "proof" originates. By volume, 57.15% alcohol has been calculated as the minimum required for it to pass the test.
Alcoholic proof in the United States is defined as twice the percentage of alcohol by volume . Consequently, 100-proof whiskey contains 50% alcohol by volume; 86-proof whiskey contains 43% alcohol, etc.