My American soldier's dog (5)
I believe the answer is:
corgi
'dog' is the definition.
(corgi is a kind of dog)
'my american soldier's' is the wordplay.
'my' becomes 'cor' (I've seen this in other clues).
'american soldier' becomes 'gi'.
'cor'+'gi'='CORGI'
(Other definitions for corgi that I've seen before include "Welsh breen of dog" , "Royal canine" , "HM's favourite dog" , "Dog popular with British royals" , "Barker?" .)