Mandela is a naval hero (6)
I believe the answer is:
nelson
I believe this clue is a double definition.
'mandela' is the first definition.
(I know that mandela given name Nelson)
'naval hero' is the second definition.
(I've seen this before)
'is a' is the link.
(Other definitions for nelson that I've seen before include "Lancashire town" , "Lady Hamilton's naval lover" , "Victorious flag officer" , "Admiral; wrestling hold" , "Lady Hamilton's navy lover" .)