What Detective Chief Superintendent typically did to get rank (6)

I believe the answer is:

rancid

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'rank' is the definition.
(I've seen this before)

I don't understand the remainder of the clue.

(Other definitions for rancid that I've seen before include "(Of fats) stale" , "Smelly and going bad" , "Foul-tasting" , "Sour like stale fat" , "Sour like stale grease 96)" .)

I've seen this clue in The Independent.

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