Rum issued in the Royal Navy in the 20th Century was generally issued watered down. The rum ration was served as a mixture of two-three parts water to one part rum. However, petty officers (and, until 1918, warrant officers) were entitled to draw their ration as neat rum. Rum could also be issued to the crew neat in extreme cases, when mixing with water was impractical due to impending action. Navy issue rum was 54.5% alcohol by volume, and was a blend of rums, mainly West Indian in origin. Demerera and Trinidad were the largest contributors, with small portions of Natal (South African), Australian and Mauritian rums as well. Not every sailor took the rum ration. Those under the age of 20 were forbidden to draw it, while older sailors could choose to take a monetary payment instead.

The rum issue was one of the major ceremonies of the typical naval day. Each morning, the rum barrel would be fetched from the spirit room (locked and guarded to prevent theft) by the duty gunner, a regulating petty officer (from the ship's police), a marine sergeant, and two supply petty officers. The barrel was opened by the ship's cooper, supervised by an officer. The rum was transferred to the 'rum tub', a lidded oak barrel emblazoned with the legend 'The King (or Queen) God Bless Him (or Her)' in brass letters. Here, it was mixed with the water for issue to the junior ratings. Once this was done, the men were called by a whistle on the bosun's pipe. The rum might be issued directly to the ratings. However, on larger ships, it was more common for each mess's ration to be collected by the senior rating in the mess in a large metal canister or 'fanny'. It would then be taken back to the mess, and each hand's ration handed out as appropriate. The ration was not supposed to be shared, but men would often share 'sippers' or the larger 'gulpers' on special occasions or in return for favours.

Officers did not draw the rum ration, but could instead purchase wine and spirits from the wardroom, the officers' mess. Gin was a particular favourite, especially Plymouth gin, a sweeter variety than the more common London gin. Gin was often drunk as a 'pink gin', with Angostura Bitters. This could be drunk neat, but water was often added. Other spirits were also available, especially on larger ships. The American naval attache Joseph Wellings, in his memoirs, includes a drinks list from the wardroom of HMS Birmingham in 1941. Rum and gin were the cheapest spirits, showing both their availability and their popularity, but brandy, whiskey, and a broad variety of fortified wines, liqueurs and wines were available for those who wanted them.