Concerning a seaman out to wreck a U-boat (5)
I believe the answer is:
about
'concerning a seaman' is the definition.
'about' can be an answer for 'concerning' (about can mean concerning or relating to). I'm not sure about the 'a seaman' bit.
'to wreck a u-boat' is the wordplay.
'to wreck' is an anagram indicator.
'u'+'boat'='uboat'
'uboat' with letters rearranged gives 'ABOUT'.
'out' is the link.
Can you help me to learn more?
(Other definitions for about that I've seen before include "Engaged in" , "Regarding" , "Concerning; roughly" , "In conection with, all around" , "round" .)