US soldier set up impressive base (7)
I believe the answer is:
ignoble
'base' is the definition.
('ignoble' can be similar in meaning to 'base')
'us soldier set up impressive' is the wordplay.
'us soldier' becomes 'gi' (I've seen this in other clues).
'set up' is a reversal indicator.
'impressive' becomes 'noble' ('noble' can be similar in meaning to 'impressive').
'gi' back-to-front is 'ig'.
'ig'+'noble'='IGNOBLE'
(Other definitions for ignoble that I've seen before include "'Far from the madding crowd's . . . . . . . strife'" , "I belong to low sort" , "Inferior" , "I belong to base sort" , "Wretched, base" .)