Request a hard ground for base (12)
I believe the answer is:
headquarters
'base' is the definition.
(I've seen this before)
'request a hard ground' is the wordplay.
'ground' indicates an anagram ('grind' the letters into a new form).
'request'+'a'+'hard'='requestahard'
'requestahard' is an anagram of 'HEADQUARTERS'.
'for' acts as a link.
(Other definitions for headquarters that I've seen before include "Administrative centre" , "Military command post" , "Military command point" , "Command centre" , "Main office" .)