Crossword Genius

Operation for which you need the right backup (4)

Ross

I believe the answer is:

raid

'operation' is the definition.
(I know that raid is a type of incursion)

'the right backup' is the wordplay.
'the right' becomes 'r' (common abbreviation).
'backup' becomes 'aid' (backup is aid or assistance).
'r'+'aid'='RAID'

'for which you need' is the link.

(Other definitions for raid that I've seen before include "Go on the attack" , "bust" , "Sally" , "Surprise police visit" , "Maraud" .)

I've seen this clue in the Evening Standard.
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