Crossword Genius

Dear sir - big upset for officers (10)

Ross

I believe the answer is:

brigadiers

'for officers' is the definition.
(brigadier is a kind of officer)

'dear sir big upset' is the wordplay.
'upset' indicates anagramming the letters.
'dear'+'sir'+'big'='dearsirbig'
'dearsirbig' anagrammed gives 'BRIGADIERS'.

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