Poem about navy's last ship needing year for journey (7)
I believe the answer is:
odyssey
'for journey' is the definition.
(odyssey is a kind of journey)
'poem about navy's last ship needing year' is the wordplay.
'poem' becomes 'ode' (ode is a type of poem).
'about' is an insertion indicator.
'last' indicates one should take the final letters.
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'needing year' becomes 'y' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
The last letter of 'navy' is 'y'.
'y'+'ss'='yss'
'ode' placed around 'yss' is 'odysse'.
'odysse'+'y'='ODYSSEY'
(Other definitions for odyssey that I've seen before include "Book" , "Epic poem - epic voyage" , "Homer epic" , "Heroic journey" , "A long adventurous, as told by Homer" .)