Tower damage? Divulge nothing! (8)
I believe the answer is:
martello
'tower' is the definition.
(I've seen this before)
'damage? divulge nothing' is the wordplay.
'damage?' becomes 'mar' (to mar is to spoil or damage).
'divulge' becomes 'tell' (I've seen this in another clue).
'nothing' becomes 'O' (O resembles 0).
'mar'+'tell'+'o'='MARTELLO'
(Other definitions for martello that I've seen before include "Small round tower once used for coastal defence" , "Circular coastal fort; more tall (anag.)" , "Tower built around Irish coasts in Napoleonic war" .)