An old bassoon in shell (7)
I believe the answer is:
bombard
This could be a double definition.
'an old bassoon' is the first definition.
'bombard' can be an answer for 'bassoon' (thesaurus). I am not certain of the 'an old' bit.
'shell' is the second definition.
(I know that shell is a is a more specific form of the action bombard)
'in' acts as a link.
Can you help me to learn more?
(Other definitions for bombard that I've seen before include "Attack with missiles" , "Attack persistently" , "not working? Keep hitting" , "Batter heavily and persistently" , "Organ stop" .)