Embarrassed by junior officer seen waving on a British vessel (3,6)
I believe the answer is:
red ensign
'waving on a british vessel' is the definition.
The definition suggests a singular noun which matches the answer.
'embarrassed by junior officer' is the wordplay.
'embarrassed' becomes 'red' (someone may blush or go red when embarrassed).
'by' means one lot of letters go next to another.
'junior officer' becomes 'ensign' (I've seen this before. I am not sure about the 'junior' bit.).
'red'+'ensign'='RED ENSIGN'
'seen' is the link.
Can you help me to learn more?
(Other definitions for red ensign that I've seen before include "Sailor's flag" , "Flag flown by the British Merchant Navy" , "Flag for ships" , "It will fly at sea" , "standard for seamen" .)