Len's crazy working for naval hero (6)
I believe the answer is:
nelson
'naval hero' is the definition.
(I've seen this before)
'len's crazy working' is the wordplay.
'crazy' indicates an anagram.
'working' becomes 'on' (on can mean working or activated).
'lens' anagrammed gives 'nels'.
'nels'+'on'='NELSON'
'for' acts as a link.
(Other definitions for nelson that I've seen before include "English admiral, lover of Lady Hamilton" , "Lady Hamilton's naval lover" , "Tar" , "mariner with dodgy vision" , "Trafalgar victor" .)