This recent story from the BBC News article shows photographs from the wreck of HMS Royal Oak, sunk in 1939. One image clearly shows the scroll of a double bass; not a common instrument by most people's standards. Was the carrying of musical instruments common? Did ships have orchestras?
Link in question - https://www.bbc.co.uk/news/uk-scotland-north-east-orkney-shetland-47072973
Royal Navy vessels would typically carry musical instruments, yes, with each major warship having a band. The ships' band was provided by the Royal Marines, which governed all musical services for the navy. A battleship's band would typically consist of 25 men, equipped with a variety of instruments. Bandsmen were drawn from two sources; peacetime recruits and wartime conscripts. In peacetime, boys interested in music were recruited by the marines and given training, while in wartime, established musicians were conscripted. The wartime conscripts were trained at bases in Yorkshire and on the Isle of Man. Marine bands typically had a wide repertoire of music beyond the typical military tunes; they would often give performances of popular music at dances aboard ship, or classical performances at more formal events. This could often include orchestral works; in 1942 at the East African port of Kilindini, the bands of HMS Warspite and Mauritius performed Sibelius' Finlandia symphony, an event which Mauritius' bandsmen remembered fondly as their best performance of the war. In battle, the band would man the 'transmitting station', the fire-control position deep in the ship where targeting data was passed from the rangefinders to the turrets.