Gung-ho gunners encircle country in Africa (6,2,2)
I believe the answer is:
raring to go
'gung-ho' is the definition.
(I've seen this before)
'gunners encircle country in africa' is the wordplay.
'gunners' becomes 'ra' (Royal Artillery).
'encircle' becomes 'ring' ('ring' can be a synonym of 'encircle').
'country in africa' becomes 'togo'.
'ra'+'ring'+'togo'='RARING TO GO'
(Other definitions for raring to go that I've seen before include "Champing at the bit" , "showing enthusiasm" , "Eager to begin" , "Gung-ho" .)