Seriously advanced encirclement of gun emplacement (9)
I believe the answer is:
earnestly
'seriously' is the definition.
(I know that seriously can be written as earnestly)
'advanced encirclement of gun emplacement' is the wordplay.
I cannot really see how this works, but
'advanced' could be 'a' (abbreviation) and 'a' is present in the answer.
'emplacement' could be 'nest' (nest is a kind of emplacement) and 'nest' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for earnestly that I've seen before include "with gusto" , "how Wilde character may be acted?" , "Zealously" , "with heart and soul" , "Sincerely and seriously" .)