Lack of interest in the body of troops (10)
I believe the answer is:
detachment
I believe this clue is a triple definition!
'lack of interest' is the first definition.
(thesaurus)
'in' is a link.
'the body' is the second definition.
(thesaurus)
'of' is a link.
'troops' is the third definition.
(I've seen this before)
(Other definitions for detachment that I've seen before include "several reserves?" , "indifference" , "reserve" , "Objective state; group of troops" , "Aloofness" .)