Notes explosives around exterior of U-boat (7)
I believe the answer is:
minutes
'notes' is the definition.
(minute is a kind of note)
'explosives around exterior of u-boat' is the wordplay.
'explosives' becomes 'mines'.
'around' is an insertion indicator.
'exterior of u-boat' becomes 'ut' (I can't explain this - if you can you should believe this answer much more).
'mines' enclosing 'ut' is 'MINUTES'.
Can you help me to learn more?
(Other definitions for minutes that I've seen before include "Written account of a meeting" , "Units of time" , "summary" , "Recorded notes of a meeting" , "Record of a meeting's decisions" .)