Feel a need, yes, for service (5)
I believe the answer is:
yearn
'feel a' is the definition.
I can't tell whether this definition defines the answer.
'yes for service' is the wordplay.
'yes' becomes 'yea' (I've seen this before).
'for' says to put letters next to each other.
'service' becomes 'RN' (abbreviation for Royal Navy).
'yea'+'rn'='YEARN'
'need' acts as a link.
Can you help me to learn more?
(Other definitions for yearn that I've seen before include "wish" , "Hanker" , "Pant - pine" , "Long - pine" , "Have a great longing" .)