Sheltered artillery brought up (4)
I believe the answer is:
snug
'sheltered' is the definition.
(thesaurus)
'artillery brought up' is the wordplay.
'artillery' becomes 'guns'.
'brought up' is a reversal indicator (in a down clue, letters go up).
'guns' back-to-front is 'SNUG'.
(Other definitions for snug that I've seen before include "Comfortabel with guns" , "joiner" , "Cosy and comfortable" , "Warm and cosy" , "Small bar in pub - warm and comfortable" .)