Cared about a military unit (5)
I believe the answer is:
cadre
'a military unit' is the definition.
(I've seen this before)
'cared about' is the wordplay.
'about' is an anagram indicator.
'cared' is an anagram of 'CADRE'.
(Other definitions for cadre that I've seen before include "Group of revolutionaries" , "Raced (anag) -- small inner group of activists" , "activist group" , "Tight-knit military unit" , "Nucleus of servicemen" .)