Being a sailor in the British Navy at any time in history probably wasn't a very enviable position, but if you were enlisted in the 19th and much of the 20th century, you could at least look forward to a cheeky, twice daily ration of rum. For centuries the Navy issued rations of beer or wine, stored in casks on the ships, but of course these would end up going bad over a long sea voyage, and over time the Navy shifted to offering distilled spirits instead. If your ship was closer to home, this would probably be a French brandy, but for the many British sailors in the Caribbean, it meant rum.
Initially they would just buy casks from wherever they could get it, but by 1815 or so, the entire navy switched to rum, buying huge amounts at a time, bringing it back to England, and blending and proofing it themselves (to 54.5%, or Navy Strength). The recipe shifted constantly over time, but eventually settled on a classic profile dominated by big, bold Demerara rum, especially from the wooden Port Mourant pot still, a slightly smaller amount of heavy column distillate from Trinidad's legendary (and now long shuttered) Caroni distillery, and then about 10% of it was from various other parts of the Caribbean. These rums were bought unaged and blended together in large, open topped wooden vats for 1-2 years in England. This would mellow the spirit considerably, but wouldn't resemble any kind of proper maturity as we are used to it today in our aged spirits. However, if you were toiling away day after day on the high seas, the stiff pleasure that a dram of Navy rum offered would surely be a welcome respite, even if you weren't quite aware you were throwing back two of the Caribbean's finest distillates, both of which would one day command the passions of many a rum drinker.