Ship capsized becomes national symbol (4)
I believe the answer is:
leek
'national symbol' is the definition.
(emblem of Wales)
'ship capsized' is the wordplay.
'ship' becomes 'keel' (literary term for a ship).
'capsized' shows that the letters should be reversed in order.
'keel' backwards is 'LEEK'.
'becomes' is the link.
(Other definitions for leek that I've seen before include "National emblem of Wales." , "One of the veggies" , "Vegetable related to onions" , "Plant related to the onion, pair with potato for soup" , "English town" .)