In military, captain’s first — plus handsome escort (3,5)
I believe the answer is:
arm candy
'handsome escort' is the definition.
I know nothing about this answer so I cannot tell whether this works.
'in military captain's first plus' is the wordplay.
'in' is an insertion indicator.
'military' becomes 'army' (the armed forces).
'captain's first' becomes 'c' (1st letter of 'captain').
'plus' becomes 'and' (I've seen this before).
'c'+'and'='cand'
'army' placed around 'cand' is 'ARM CANDY'.
Can you help me to learn more?
(Other definitions for arm candy that I've seen before include "sexy companion?" , "beautiful girl" .)