Bombards lower regions on board ship (6)
I believe the answer is:
shells
'bombards' is the definition.
(shelling is a kind of bombarding)
'lower regions on board ship' is the wordplay.
'lower regions' becomes 'hell' (I have seen 'Infernal regions' mean 'hell' so perhaps 'regions' could also mean 'hell'. I am not sure about the 'lower' bit.**).
'on board' is an insertion indicator.
'ship' becomes 'ss'.
'hell' put within 'ss' is 'SHELLS'.
Can you help me to learn more?
(Other definitions for shells that I've seen before include "Racing boats" , "Carapaces or military missiles" , "Hard outer coatings or metal casings" , "Collect them on the seashore" , "Hard protective structures" .)