Second U-boat base blown up by her, ultimately (8)
I believe the answer is:
saboteur
'second' is the definition.
The definition and answer can be both people as well as being singular nouns.
Maybe there's an association between them I don't understand?
'u-boat base blown up by her ultimately' is the wordplay.
'boat' becomes 'e'.
'base' is an anagram indicator (base can mean impure or corrupt).
'blown up' becomes 'sabot' (I can't explain this - if you can you should give a lot more credence to this answer).
'by' is a charade indicator (letters next to each other).
'ultimately' says to take the final letters.
The last letter of 'her' is 'r'.
'u'+'e'='ue'
'ue' is an anagram of 'eu'.
'eu' after 'sabot' is 'saboteu'.
'saboteu'+'r'='SABOTEUR'
Can you help me to learn more?
(Other definitions for saboteur that I've seen before include "He destroys in order to subvert" , "One engaged in malicious disruption" , "One who deliberately subverts" , "Deliberate destroyer" , "Abort use (anag)" .)