Flier needing good cover with soldiers returning (6)
I believe the answer is:
glider
'flier' is the definition.
(I have seen 'quiet flier' mean 'glider' so perhaps 'flier' could also mean 'glider')
'good cover with soldiers returning' is the wordplay.
'good' becomes 'g' (abbreviation).
'cover' becomes 'lid' (lid is a kind of cover**).
'with' says to put letters next to each other.
'soldiers' becomes 're' (Royal Engineers).
'returning' says the letters should be written in reverse.
're' written backwards gives 'er'.
'g'+'lid'+'er'='GLIDER'
'needing' is the link.
(Other definitions for glider that I've seen before include "Sailplane" , "A sort of possum" , "Unpowered plane" , "craft without power" , "Flying machine without engine" .)