Carried on one’s service, without getting ahead (4)
I believe the answer is:
worn
'carried on one's' is the definition.
(ie worn on one's person)
'service without getting ahead' is the wordplay.
'service' becomes 'RN' (abbreviation for Royal Navy).
'without' becomes 'wo' (abbreviation of 'without', normally with a slash).
'getting ahead' is a charade indicator (letters next to each other) (some letters go in front of others).
'rn' put after 'wo' is 'WORN'.
(Other definitions for worn that I've seen before include "Showing the effects of use" , "Threadbare" , "Second-hand" , "Looking tired and exhausted" , "Shabby" .)