Butterflies embarrassed naval officers (3,8)
I believe the answer is:
'butterflies' is the definition.
(red admiral is a kind of butterfly)
'embarrassed naval officers' is the wordplay.
'embarrassed' becomes 'red' (I've seen this before).
'naval officers' becomes 'admirals' (admiral is a kind of officer. I am not sure about the 'naval' bit.).
Can you help me to learn more?
(Other definitions for red admirals that I've seen before include "Insects", "Butterflies".)