In the Royal Navy, much of Napoleonic life remained well into the 20th Century. If you plunked Jack Aubrey down in 1914 or 1940, while he would be confused by the different ships, he would recognise much of the daily routine.

Until the 1950s, many officers entered the navy young. One of the main pathways for becoming an officer was through the Royal Naval College (RNC). Those who followed this pathway joined the navy aged 13. They would be trained ashore for four years, following a typical public school curriculum, albeit with a technical bias and with some naval training added. At about age 17, they would be promoted to midshipman. Following this promotion, they would spend some time at sea gaining experience of command, typically aboard a cruiser or battleship. Their shore education would continue. They would also spend time learning the duties the seamen under their command would fulfil aboard the training ships, like the cruiser Vindictive. In 1948, the age for entering the Royal Naval College was raised to 16, and in 1955, it was raised to 17. The other main pathway was the 'Special Entry' scheme, which took public school graduates aged 18. They were selected following a strict examination, and spent five months catching up with the RNC boys. Then they would be promoted to midshipman, where they followed the same path as their counterparts from the RNC. A midshipman would be promoted to sub-lieutenant aged around 20, and would begin to specialise from there.

In peacetime, the RN typically recruited ratings young. Until 1973, when the school leaving age was raised to 16, many entered the navy aged just 15. They would be trained at shore establishments like HMS Ganges, before joining the fleet aged 16-17. They would remain with the fleet for at least 12 years from age 18, with the option to sign on for another 10 year hitch, which got them a pension from age 40. Even today, though, it is still possible to join the RN aged 16, though this needs parental consent. During WWI and WWII, however, the RN recruited many men for short-term 'Hostilities Only' service. These men were typically aged between 18-40.

Other aspects of the Royal Navy remained the same as they had been in the Napoleonic period. Until the 1950s-60s, the ratings still slept in hammocks, with the same 14 inches of space allocated per man as had been allocated in the Napoleonic period. The system for preparing food remained in the Napoleonic mode lasted throughout the First World War, and lingered on many ships until after WWII. In this, each mess was given a standard ration, plus a messing allowance with which they could augment it. Each mess allocated cooks on a rotating basis; these cooks were responsible for preparing the food for the mess, before taking it to the ship's cook for cooking. This began to be replaced by more centralised methods in the years after WWI. At first, it was replaced with the 'General Messing' system. Here food was prepared and cooked in the galley by the cooks, before being collected by the mess cooks. This was then supplanted by 'Cafeteria Messing', where the food was prepared and cooked in the galley, and eaten in an adjoining cafeteria.