New US prisons somehow gain distinction (3,4,5)
I believe the answer is:
win ones spurs
'gain distinction' is the definition.
(I've seen this before)
'new us prisons somehow' is the wordplay.
'somehow' indicates anagramming the letters.
'new'+'us'+'prisons'='newusprisons'
'newusprisons' with letters rearranged gives 'WIN ONES SPURS'.
(Other definitions for win ones spurs that I've seen before include "to achieve distinction" , "Gain distinction" .)