Supply lines effective in expedition (6)
I believe the answer is:
prompt
I believe this clue is a double definition.
'supply lines' is the first definition.
(I've seen this before)
'effective in expedition' is the second definition.
(I've seen this before)
(Other definitions for prompt that I've seen before include "Immediate - supply actor's lines" , "Incite - punctual" , "Punctual or timely" , "Encourage" , "Cue; punctual" .)