Artillery unit in an assault? (7)
I believe the answer is:
battery
I believe this is a triple definition!
'artillery' is the first definition.
(battery is a kind of artillery)
'unit' is the second definition.
(battery is a kind of unit)
'in' acts as a link.
'an assault?' is the third definition.
('battery' can be a synonym of 'assault')
(Other definitions for battery that I've seen before include "Source of charge" , "Personal attack" , "Accumulator" , "associated with assault" , "Group of cells (or guns)" .)