Deserter, one retreating behind curt Guy Gibson, perhaps (6)
I believe the answer is:
guitar
'guy gibson perhaps' is the definition.
I can't judge whether this defines the answer.
'deserter one retreating behind curt' is the wordplay.
'deserter' becomes 'rat' (both can mean a traitor).
'one retreating' says the letters should be written in reverse.
'behind' is a charade indicator (letters next to each other).
'curt' becomes 'gui' (I can't justify this - if you can you should give a lot more credence to this answer).
'rat' written backwards gives 'tar'.
'tar' after 'gui' is 'GUITAR'.
Can you help me to learn more?
(Other definitions for guitar that I've seen before include "Talk under one's breath" , "Perhaps Spanish" , "Axe" , "It's plucked or strummed" , "Six- or 12-stringed instrument" .)