Before the 17th century each sailor was allowed 1 gallon of beer per day.
Since the logistics of the storage of all this beer presented a problem, admirals introduced brandy instead of beer in the mid 1600's.
In 1655, Vice-Admiral William Penn captured Jamaica and began the use of the rum ration.
Why? Well, the Jamaicans weren't big on beer and wine, but had plenty of rum for the taking.
In 1731, rum became part of the "Regulations and Instructions Relating to His Majesty's Service at Sea." The regulations specified that 1 half-pint of rum was equivalent to the 1 gallon of beer.
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