Expression of surprise over soldier’s dog (5)
I believe the answer is:
corgi
'dog' is the definition.
(corgi is a kind of dog)
'expression of surprise over soldier's' is the wordplay.
'expression of surprise' becomes 'cor' (I've seen this before).
'over' means one lot of letters go next to another.
'soldier' becomes 'gi' (government issue or general issue).
'cor'+'gi'='CORGI'
(Other definitions for corgi that I've seen before include "pet in 9 [CARDIFF]?" , "Dog of Welsh breed, royal favourite" , "Cardigan or Pembroke dog" , "Welsh breen of dog" , "Small Welsh dog with fox-like head" .)