Royal Artillery’s turned up in dark to surrender weapons (6)
I believe the answer is:
disarm
'surrender weapons' is the definition.
'royal artillery's turned up in dark' is the wordplay.
'royal artillery's' becomes 'ras'.
'turned up' shows that the letters should be reversed in order.
'in' is an insertion indicator.
'dark' becomes 'dim' ('dim' can be similar in meaning to 'dark').
'ras' written backwards gives 'sar'.
'sar' placed inside 'dim' is 'DISARM'.
'to' is the link.
(Other definitions for disarm that I've seen before include "Make less angry or deprive of weapons" , "Placate" , "Take weapons from or captivate" , "Render harmless" , "Take away weapons or win over" .)