Originally called “kill-devil”, rum was widely known as ‘rum’ by 1654, the year before Jamaica was captured by the English from the Spanish. 

Well known 17th century diarist Samuel Pepys was also Chairman of the Navy Board and responsible for many navy reforms. In 1686 he recommended that the King James Navy use rum as their daily drink on their ships in Jamaica instead of brandy.
Sailors would try and smuggle rum aboard their ships; leading to the word rummage, originally meaning a search for contraband rum.
Rum acquired the nickname "Nelson's Blood" after the Battle of Trafalgar in 1805. To preserve Lord Nelson’s body, it was placed in a barrel of rum. Legend has it that when some sailor's learned of this, they drank the rum.
The days of the rum ration ended in the American Navy in 1862, but not for the British until January 28, 1970, when the “Great Rum Debate” took place in the House of Commons, rendering the Royal Navy free of the rum ration.