Style for service gets go-ahead (6)
I believe the answer is:
modern
'go-ahead' is the definition.
'style for service' is the wordplay.
'style' becomes 'mode' ('mode' can be a synonym of 'style'**).
'for' means one lot of letters go next to another.
'service' becomes 'rn' (abbreviation for Royal Navy).
'mode'+'rn'='MODERN'
'gets' acts as a link.
(Other definitions for modern that I've seen before include "Novel" , "See 11" , "Recent, up to date" , "'Contemporary, up-to-the-minute (6)'" , "Belonging to the present or recent times" .)