Ultrafine service? (3)

I believe the answer is:

raf

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'service?' is the definition.
(Royal Air Force)

'ultrafine' is the wordplay.
'RAF' is hidden in amongst the letters.
But, I'm uncertain how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for raf that I've seen before include "Airforce of Great Britain" , "It fought Battle of Britain" , "Royal Air Force (abbr.)" .)

I've seen this clue in the Evening Standard.

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