Indifference shown by part of army (10)
I believe the answer is:
detachment
I believe this clue is a triple definition!
'indifference' is the first definition.
(I know that detachment is a type of indifference)
'shown by' acts as a link.
'part' is the second definition.
(thesaurus)
'of' acts as a link.
'army' is the third definition.
(thesaurus)
(Other definitions for detachment that I've seen before include "squad" , "Aloofness" , "inclination to keep to the objective" , "Disengagement" , "several reserves?" .)