Single or double-decker, possibly returning with injured airmen (6,9)
I believe the answer is:
yellow submarine
'single' is the definition.
(Beatles single)
'or double-decker possibly returning with injured airmen' is the wordplay.
'or' becomes 'yellow' ('or' is the heraldic name for gold or yellow**).
'double-decker possibly' becomes 'bus'.
'returning' says the letters should be written backwards.
'with' means one lot of letters go next to another.
'injured' is an anagram indicator.
'bus' back-to-front is 'sub'.
'airmen' with letters rearranged gives 'marine'.
'yellow'+'sub'+'marine'='YELLOW SUBMARINE'
(Another definition for yellow submarine that I've seen is " Beatles' film".)