It can be confusing to know where to look for Royal Naval service records, but if your relative was either a permanent full-time sailor in the Royal Navy or was called up in a ‘Hostilities Only’ capacity during the Second World War or Korea, and did not form part of the other formations mentioned on this page, this is probably your best starting point.  If you are looking for an officer you can check in the Navy List to see which branch of service he is listed under.   
 
Records of Royal Navy ratings who enlisted before 1923 can be found at The National Archives in record class ADM 188.  Officers’ First World War records can be found in ADM 196.

The Fleet Air Arm Museum has holdings of the engagement papers of Royal Navy ratings, serving between 1888 and 1923.

Records of executive officers whose service began after 1917; records of regular officers and ratings in service up to 1950; warrant officers whose service began after 1931; and of ratings in service from 1924 are currently held by:

Navy Search
TNT Archives Services
Tetron Point
William Nadin Way
Swadlincote
Derbyshire DE11 0PB

For service records covering ‘Hostilities Only’ service from 1939 (i.e. those taken on solely for service during the Second World War and Korea), and of regular officers and ratings in service after 1950, please write to:

PPPA (Pay, Pensions, Personnel, Administration)
Centurion Building
Grange Road
Gosport
Hampshire PO13 9XA.